Preparing an unsaturated carboxylic acid salt from an alkene and carbon dioxide using a covalently immobilized transition metal complex

Description

The present invention relates to a process for preparing an ^-ethylenically unsaturated carboxylic acid salt by carboxylation of an alkene. More particularly, the invention relates to a process for preparing sodium acrylate by direct carboxylation of ethene with carbon dioxide (CO2). Acrylic acid and derivatives thereof are important industrial chemicals and monomer units for production of water-absorbing resins, called super- absorbents.

The direct addition of CO2 onto ethylene to give acrylic acid is industrially unattractive due to thermodynamic limitations (ΔΘ = 42.7 kJ/mol at 298 K) and the unfavorable equilibrium, which at room temperature is virtually completely to the side of the reac- tants (K298 = 7 x 10 ^"7 ). On the other hand, the formation of sodium acrylate and water from CO2, ethylene and sodium hydroxide is thermodynamically favored (ΔΘ = -56.2 kJ/mol at 298 K, K298 = 7.1 ^χ 10 ⁹ ). By using a base, it is thus possible to convert the a^-ethylenically unsaturated acid to the salt thereof and thus to shift the equilibrium to the side of the products. The reaction, however, is kinetically inhibited and therefore requires a homogeneous or heterogeneous carboxylation catalyst (Buntine eta/., Or- ganometallics 2007, 26, 6784).

The stoichiometric coupling of CO2 and ethene at homogeneous Nickel complexes has been known since more than 30 years (Hoberg eta/., J. Organomet. Chem. 1983, C51 ). The formation of nickelalactones as intermediates has been discussed, e.g. by Walther eta/. {Chem. Commun. 2006, 23, 2510-2512). These do not spontaneously decompose by ^-hydride elimination, as according to Walther's initial theory. Many nickelalactones are particularly stable and obtained in the form of solids by stoichio- metric coupling of CO2 and ethene {J. Organomet. Chem. 1983, C51 ; J. Organomet. Chem. 1982, 236, C28; Angew. Chem. Int. Ed. Engl. 1987, 26, 771 ). Some nickelalactones may even be isolated at room temperature in the form of stable solids {J. Organomet. Chem. 1982, 236, C28). The choice of an appropriate transition metal comprising carboxylation catalyst is very important in order to obtain an ^-ethylenically unsaturated carboxylic acid salt from an alkene and carbon dioxide in the presence of a base. The intermediate metallalactone formed with the transition metal comprising carboxylation catalyst must be base- cleavable. Homogeneous transition metal-alkene complexes have been successfully applied by Limbach eta/. (WO 2013/098772, Chem. Eur. J. 2012, 18, 14017) in the first catalytic process for the synthesis of an ^-ethylenically unsaturated carboxylic acid salt from an alkene and carbon dioxide. In this process, the transition metal-alkene complex is first reacted with CO2 to give a metallalactone. The metallalactone is reacted with a base selected from alkali metal or alkaline earth metal hydroxides and alkali metal or alkaline earth metal superbases, to give an adduct of the alkali metal or alkaline earth metal salt of the ^-ethylenically unsaturated carboxylic acid with the transition metal complex. The adduct is then reacted with an alkene to release the alkali metal or alkaline earth metal salt of the ^-ethylenically unsaturated carboxylic acid and regenerate the transition metal-alkene complex.

The use of a homogeneous catalyst, and alternatively also of a heterogeneous catalyst, has been suggested in WO 201 1/107559. Therein, a process is disclosed, wherein a) an alkene, CO2 and a carboxylation catalyst are converted to an alkene/C02/ carboxy- lation catalyst adduct, b) the adduct is decomposed to release the carboxylation catalyst with an auxiliary base to give the auxiliary base salt of the ^-ethylenically unsaturated carboxylic acid, c) the auxiliary base salt of the ^-ethylenically unsaturated car- boxylic acid is reacted to release the auxiliary base with an alkali metal or alkaline earth metal base to give the alkali metal or alkaline earth metal salt of the ^-ethylenically unsaturated carboxylic acid. The heterogeneous catalyst may be a supported catalyst that is prepared by an impregnation processes, adsorption processes, precipitation processes, or mechanical processes. The use of a heterogeneous catalyst is not ex- emplified and homogeneous catalysts are preferred. Using a homogeneous catalyst, 0.01 mmol of acrylate was obtained at an overall yield of 40% based on the decomposed metallalactone (0.025 mmol).

The a^-ethylenically unsaturated carboxylic acid salt is obtained in the process of WO 2013/098772 in a reaction medium containing the dissolved catalyst. The separation of the catalyst from the product needs much effort, i.e. a liquid-liquid phase separation, with the product being enriched in one phase and the transition metal-alkene complex being enriched in the other phase. As enrichment of the product and the catalyst in the respective phase is not expected to be 100%, the quantitative separation of product and catalyst is difficult to achieve by liquid-liquid phase separation. Contamination of the product with traces of transition metal is thus likely to occur. Such contamination is a problem in particular when the product is to be processed further into sanitary products, i.e. diapers. In the process of WO 201 1/107559, the yield of

a^-ethylenically unsaturated carboxylic acid salt needs to be improved further. It is an object of the present invention to provide an efficient processes for preparing a^-ethylenically unsaturated carboxylic acid derivatives from CO2 and an alkene such that the reaction medium comprising the crude derivative can be processed with little effort to obtain the carboxylic acid derivative at a purity level suitable for further processing into sanitary products.

The invention provides a process for preparing an ^-ethylenically unsaturated carboxylic acid salt, comprising, reacting an alkene and carbon dioxide in the presence of a carboxylation catalyst and releasing the ^-ethylenically unsaturated carboxylic acid salt with a base, wherein the carboxylation catalyst comprises a transition metal complex that is covalently immobilized on a solid support.

The transition metal complex is not only adsorbed to the surface of the solid support but immobilized covalently. Generally, at least one ligand moiety coordinated to the transition metal is bound via a covalent bond or a sequence of covalent bonds (and intervening atoms) to the solid support. This is an important difference to conventional supported heterogeneous catalysts, wherein active metals are only adsorbed to the surface of the support but not covalently immobilized. Non-covalent immobilization can lead to undesirable leaching of active metal into the reaction medium.

Suitable alkenes are those of the following general formula

wherein

R ^a , R ^b and R ^c are each independently hydrogen, Ci-12-alkyl, C2-i2-alkenyl, or R ^a and R ^b together with the carbon atoms to which they are bonded are a mono- or dieth- ylenically unsaturated, 5- to 8-membered carbocycle.

Suitable alkenes are, for example, ethene, propene, isobutene, butadiene, piperylene, 1 -butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -octene, 1 -nonene, 1 -decene, 2-butene, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclooctadiene, or styrene. The alkene to be used in the carboxylation is generally gaseous or liquid under the reaction conditions.

In a preferred embodiment, the alkene is ethene. The process according to the inven- tion makes it possible to obtain an acrylate.

In another embodiment, the alkene is piperylene and a sorbate is obtained.

The alkene partial pressure is for example between 0.5 and 200 bar, preferably be- tween 1 and 100 bar, in particular between 2 and 80 bar.

All pressures indicated herein are absolute pressures.

The CO2 for use in the reaction can be used in gaseous, liquid or supercritical form. It is also possible to use carbon dioxide-comprising gas mixtures available on the industrial scale, provided that they are substantially free of carbon monoxide.

CO2 and alkene may also comprise inert gases such as nitrogen or noble gases. Advantageously, however, the content thereof is below 10 mol%, based on the total amount of carbon dioxide and alkene in the reactor.

The carbon dioxide partial pressure is for example between 0.5 and 200 bar, preferably between 2 and 150 bar, in particular between 3 and 100 bar. The molar ratio of carbon dioxide to alkene in the feed is generally 0.1 to 10 and preferably 0.5 to 5.

Preferably, the ratio of carbon dioxide partial pressure to alkene partial pressure is in the range from 0.1 to 10, for example, in the range from 0.5 to 5, in particular in the range from 1 to 4.

The term "transition metal complex" used herein comprises, in a generic manner, all transition metal complexes through which the catalytic cycle is supposed to pass, i.e. transition metal-alkene complexes, metallalactones and adducts wherein the a^-ethylenically unsaturated carboxylic acid salt coordinates to the transition metal.

In general, the transition metal complex comprises, as the active metal, at least one element of groups 4 (preferably Ti, Zr), 6 (preferably Cr, Mo, W), 7 (preferably Re), 8 (preferably Fe, Ru), 9 (preferably Co, Rh) and 10 (preferably Ni, Pd, Pt) of the Periodic Table of the Elements. Preference is given to nickel, cobalt, iron, rhodium, ruthenium, palladium, platinum, rhenium, tungsten. Particular preference is given to nickel, palladium, platinum, cobalt, rhodium, ruthenium. Most preferably, the transition metal complex is a palladium or a nickel complex, in particular a nickel complex.

The role of the active metal consists in the activation of CO2 and the alkene in order to form a C-C bond between CO2 and the alkene. It is assumed that a metallalactone is formed within the catalytic cycle from the alkene, carbon dioxide and the transition metal complex. The expression "metallalactone" denotes, according to the exchange nomenclature ("a" nomenclature), a lactone (y-lactone) in which a carbon atom has been exchanged for a metal atom. The expression "metallalactone" should be interpreted broadly and may comprise compounds with structures similar to a Hoberg complex, or related compounds of oligomeric or polymeric structure. The expression shall comprise isolable compounds and (unstable) intermediates.

An exemplary metallalactone that is covalently immobilized on a solid support is illustrated by the following general formula

in which

M is the transition metal,

L is a ligand moiety coordinated to the transition metal of the immobilized metallalactone,

L' is independently a ligand,

p is 0, 1 , 2, or 3,

A is a bond or a linking moiety,

G is an anchoring group,

k is O or l ,

^* is the site of attachment to the solid support, and

R ^a , R ^b and R ^c are each independently hydrogen, Ci-12-alkyl, C2-i2-alkenyl, or R ^a and R ^b together with the carbon atoms to which they are bonded are a mono- or dieth- ylenically unsaturated, 5- to 8-membered carbocycle. It is assumed that the base deprotonates the metallalactone at the a-carbon atom. The a-carbon atom is the carbon atom bound to the carbonyl carbon atom. The transition metal complex comprises a ligand moiety coordinated to the transition metal of the immobilized transition metal complex. The ligand moiety is covalently immobilized on the solid support.

The loading of the solid support is, for example, from 0.001 to 10 mmol/g, preferably from 0.002 to 8 mmol/g, in particular from 0.005 to 5 mmol/g, most preferably from 0.01 to 2 mmol/g. The unit "mmol/g" specifies the molar amount of covalently immobilized ligand moiety per gram of carboxylation catalyst.

The carboxylation catalyst may, for example, comprise structural units of the general formula (IVa)

^* -[G]k-A-LM(L')n (IVa) wherein

M is the transition metal,

L is the ligand moiety coordinated to the transition metal of the immobilized transition metal complex,

L' is a ligand,

n is 0, 1 , 2, or 3,

A is a bond or a linking moiety,

G is an anchoring group,

k is 0 or 1 , and

^* is the site of attachment to the solid support. Immobilization of the ligand moiety generally involves the use of a linking moiety. Any linking moiety that is inert under the conditions of the reaction of the alkene and carbon dioxide, to which the ligand moiety can be covalently bound and to which the solid support can be covalently bound directly or via an anchoring group, is a suitable linking moiety. The linking moiety allows for the covalent linkage of the ligand moiety and pro- vides accessibility of the immobilized transition metal for the reactant molecules.

The linking moiety, and in particular the linking moiety A, is preferably selected from -(CH ₂ )h-C6H4-(CH ₂ )h-, (CH ₂ )r, -0-(CH ₂ )r, -(CH ₂ )i-0-(CH ₂ )i-, and -0-(CH ₂ )rO- (CH ₂ )r, polyalkyleneoxides, polyamides, and polyolefins, wherein each f is inde- pendently an integer from 2 to 20, each h is independently an integer from 0 to 16, and each i is independently an integer from 2 to 10. The linking moiety can also be branched such that more than one subunits LM(L') _n may be immobilized by one linking moiety.

If the solid support per se does not carry suitable functional groups for covalent attachment, an anchoring group G is preferably used to facilitate attachment. Any anchoring group G that is inert under the conditions of the reaction of the alkene and carbon dioxide, and to which the ligand moiety can be covalently bound directly or via a linking moiety, and to which the solid support can be covalently bound, is a suitable linking moiety. Suitable reactants introducing anchoring groups onto inorganic supports such as silica are, e.g., functionalized silanes, such as haloalkyl trialkoxysilanes.

Every solid inorganic or organic material that is inert under the conditions of the reac- tion of the alkene and carbon dioxide, and to which the ligand moiety can be covalently bound (optionally via a linking moiety and/or an anchoring group), is a suitable solid support.

Refractory oxides, for example zinc oxide, zirconium oxide, cerium oxide, cerium zirco- nium oxides, silica, alumina, silica-alumina, zeolites, sheet silicates, hydrotalcites, magnesium oxide, titanium dioxide, tungsten oxide, calcium oxide, iron oxides, for example magnetite, nickel oxides or cobalt oxides may, for example, be used as solid supports. Alternative solid supports are crosslinked polymers. The solid support is preferably a silica or a crosslinked polymer. Among the crosslinked polymers, cross- linked polystyrenes are preferred.

When the linking moiety is attached to a refractory oxide solid support, a reactant introducing an anchoring group is reacted with the surface of the refractory oxide, i.e. silica, and, optionally, a functional group of the anchoring group is further reacted with a reac- tant introducing an additional linking moiety. When the linking moiety is attached to a crosslinked polymeric solid support, a reactant introducing the linking moiety is reacted with a functional group of the crosslinked polymer.

A suitable crosslinked polymer may be functionalized with any functional group that facilitates the formation of a bond from the support to the linking moiety. The functional group bound to the linking moiety attaching to the solid support may, for example, be a leaving group, i.e. halogen, that is displaced by a nucleophilic group bound to the solid support. The functional group bound to the linking moiety attaching to the solid support may, for example, be a nucleophilic group that displaces a leaving group, i.e. halogen, bound to the solid support. The functional group bound to the linking moiety attaching to the solid support may, for example, be transformed into another functional group by reaction with the solid support, e.g., an isocyanate may become a urea or carbamate, an ester may become an amide, and a thiol may become a disulfide. Alternatively, the functional group bound to the linking moiety attaching to the solid support will remain of the same type, e.g., a phosphate, phosphonate, or organosilane may remain a phosphate, phosphonate, or organosilane, albeit with different substituents.

The functional group bound to the linking moiety may, for example, be organosilane, ester, amino, hydroxyl, isocyanate, halogen, sulfate, sulfonic acid, phosphate, phosphonate, phosphonic acid or carboxy or a salt thereof.

When the solid support is selected from refractory oxides, and in particular, when it is silica, the carboxylation catalyst preferably comprises structural units of the general formula (IVb)

(IVb) wherein

m is 0, 1 , or 2,

R ⁴⁰ is H or branched, unbranched or cyclic Ci-Ci6-alkyl,

A is a linking moiety, and

M, L, L', n, and ^* are each as already defined.

In formula (IVb), the linking moiety is anchored via a siloxy anchoring group to the silica support. Tetravalency of the silicon atom results from the oxygen bridges to the solid support and any unreacted residues -OR ⁴⁰ .

In formula (IVb), the linking moiety A is preferably selected from -(CH2)r, -0-(CH2)r, -(CH2)i-0-(CH2)r, -0-(CH2)i-0-(CH2)r, polyalkyleneoxides, polyamides, and polyolefins, in particular from -(CH2)r, -(CH2)i-0-(CH2) , and polyolefins, wherein each f is independently an integer from 2 to 20 and each i is independently an integer from 2 to 10. When the solid support is a crosslinked polymer, a preferred carboxylation catalyst comprises structural units of the general formula (IVc)

(IVc),

wherein

A is a bond or a linking moiety, for example a C2-C24 alkylene group which may be interrupted by one or more than one oxygen atoms, and/or which may be interrupted by a 1 ,4-phenylene group, and

M, L, L', and n are each as already defined.

When the solid support is a crosslinked polystyrene, a preferred carboxylation catalyst comprises structural units of the general formula (IVd)

(IVd),

wherein

A is a bond or a linking moiety, and

M, L, L', and n are each as already defined. n formula (IVd), the linking moiety A is preferably selected from -(CH2) , -0-(CH2)r, 0-(CH2)i-0-(CH2)r, polyalkyleneoxides, polyamides, and polyolefins, in particular from -(CH2)r, -(CH2)i-0-(CH2)r, and polyolefins, wherein r is an integer from 1 to 10, each f is independently an integer from 2 to 20, and each i is independently an integer from 2 to 10. The solid support can be in the form of powder, granules or tablets, or in another form known to those skilled in the art.

The ligand moiety, i.e. L, may, for example, coordinate to the transition metal via at least one atom selected from P, N, O, and C.

The ligand moiety preferably comprises at least one phosphorus atom which coordinates to the transition metal. The ligand moiety may be monodentate or polydentate, for example bidentate. The polydentate, e.g. bidentate, ligand moiety may coordinate to the transition metal to form a four-, five-, six-, seven-, or eight-membered ring, i.e. the transition metal, the atoms which coordinate to the transition metal and the atoms of the shortest chain which connects the atoms coordinating to the transition metal together form a four-, five-, six-, seven-, or eight-membered ring. Ligand moieties that coordinate to the tran- sition metal to form a five-, six-, or seven-membered ring are preferred. Alternatively, the atoms which coordinate to the transition metal may be directly bound to carbon atoms of two cyclopentadienyl ligands bound to a second metal, i.e. iron.

In ligand moieties that coordinate to the transition metal via at least one phosphorus atom, at least one residue is preferably bound via a secondary or tertiary carbon atom to a transition metal coordinating phosphorus atom of the ligand moiety. More particularly, at least two residues are preferably bound to the phosphorus atom via a secondary or tertiary carbon atom. The term tertiary carbon atom as used herein also includes aromatic carbon atoms. Suitable residues bound to the phosphorus atom via a sec- ondary or tertiary carbon atom are, for example, adamantyl, tert-butyl, sec-butyl, iso- propyl, cyclohexyl, cyclopentyl, phenyl, tolyl, xylyl, mesityl, naphthyl, fluorenyl, or an- thracenyl, especially tert-butyl, isopropyl, cyclohexyl, or cyclopentyl. At least one residue is preferably bound via a primary carbon atom to a transition metal coordinating phosphorus atom. Suitable residues bound to the phosphorus atom via a primary car- bon atom are, for example, methyl, 1 -ethyl, 1 -propyl, 1 -butyl.

The ligand moiety may, for example, be derived from one of the ligands (lla), (lib), (lie), (lid), (lie), (llf), (llg), or (llh) described below. Preferred ligand moieties are derived by replacing one hydrogen atom of these ligands by a bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support.

When a covalent bond is formed between the ligand moiety and the linking moiety, a functional group of the ligand moiety is reacted with a functional group bound to the linking moiety. For example, a nucleophilic group of the ligand moiety can displace a leaving group, i.e. halogen, of the linking moiety. A phosphine ligand can, for example, be protected with BH3 and then reacted with a chlorine or bromine substituted linking moiety in the presence of a strong base, i.e. a lithium alkyl. This results in the formation of a covalent bond between the ligand moiety and the linker moiety.

Suitable monodentate ligand moieties are, for example, derived from ligands of formula (lie) wherein

R ^4a , R ^4b , and R ^4c are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, individual hydrogen atoms may independently be replaced by CI, Br, I, or F, and two or all three residues may be covalently bound to one another.

R ^4a , R ^4b , and R ^4c are preferably independently Ci-Ci ₂ -alkyl, C ₃ -Ci ₂ -cycloalkyl, or C ₃ - Ci4-aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I, F, d-Cs-alkyl and Ci- C ₄ -alkoxy.

R ^4a , R ^4b , and R ^4c are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl) propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2- methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 - decyl, 1 -undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chloro- phenyl or anisyl.

Examples of suitable ligands of formula (lie) are trialkylphosphines, i.e.

tri-n-propylphosphine, tri-n-butylphosphine, tri-tert-butylphosphine, trioctylphosphine; tricycloalkylphosphines, i.e. tricyclohexylphosphine, tricyclododecylphosphine; tri- arylphosphines; i.e. triphenylphosphine, tritolylphosphine, tri(methoxyphenyl)phosphine, trinaphthylphosphine, di-(chlorphenyl)-phenylphosphine; and dialkylarylphosphines, i.e. diethylphenylphosphine, dibutylphenylphosphine.

In preferred ligand moieties derived from ligands of formula (lie), a hydrogen atom at a phosphorus-bound carbon atom (a hydrogen atom in a-position relative to a phosphorus atom) is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support. Alternatively, in case of an aryl substituted phosphorus atom, an aromatic hydrogen at the ortho- position to the phosphorus atom may, for example, be replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support.

The transition metal complex preferably comprises a bidentate Ρ,Ρ, Ρ,Ν, P,0, or P,carbene ligand moiety that is covalently immobilized on the solid support. In pre- ferred bidentate P,P ligand moieties, the phosphorus atoms are separated by 2 to 4 bridging atoms that may optionally be part of at least one 5- to 7-membered cyclic substructure.

The phosphorus atoms being "separated by 2 to 4 bridging atoms" means that the shortest chain which connects the coordinating phosphorus atoms comprises 2 to 4 atoms.

In preferred bidentate P,P ligand moieties, wherein the bridging atoms are part of at least one 5- to 7-membered cyclic substructure, each bridging atom directly linked to a P atom, together with the P atom to which it is linked, is part of a 5- to 7-membered cyclic substructure; or two neighbouring bridging atoms are part of a 5- to 7-membered cyclic substructure.

Preferred bidentate P,P ligand moieties are derived from ligands of formula (I la)

wherein

R ⁶ is independently selected from CHR ⁷ 2, CR ⁷ 3, C3-Cio-cycloalkyl, and optionally alkylated aryl having 6 to 18 carbon atoms,

R ⁷ is independently selected from Ci-C4-alkyl, preferably linear Ci-C4-alkyl,

A ¹ together with the carbon atoms to which it is bound and the interjacent phosphorus atom forms a 5- to 7-membered cyclic substructure, and

R ⁸ is independently selected from hydrogen, Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, C3-C12- heterocycloalkyl, C6-Ci4-aryl, C6-Ci4-heteroaryl, Ci-Ci2-alkoxy, C3-C12- cycloalkoxy, C3-Ci2-heterocycloalkoxy, C6-Ci4-aryloxy, and C6-Ci4-heteroaryloxy.

A ¹ is preferably selected from -(CR ⁸ ₂ ) _r - and -(CR ⁹ =CR ⁹ ) _S - with both R ⁹ being on the same side of the double bond, wherein R ⁸ is independently selected from H, C1-C3- alkyl, and -0-Ci-C3-alkyl, R ⁹ is selected from H and Ci-C3-alkyl, or at least two R ⁹ constitute a brid e of one of the formulae:

r is 2 or 3, and s is 1 or 2.

R ⁶ is preferably independently selected from CHR ⁷ 2, CR ⁷ 3, and Cs-Cs-cycloalkyl, most preferably CR ⁷ 3.

R ⁷ is preferably methyl.

R ⁸ is preferably H.

A ¹ is preferably selected from ethylene, ethenylene, 1 ,2-phenylene, 1 ,2-naphthylene, 2,3-naphthylene, and the following formulae:

In preferred ligand moieties derived from ligands of formula (lla), a hydrogen atom at a phosphorus-bound carbon atom is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support. Alternatively, in case of an aryl substituted phosphorus atom, an aromatic hydro- gen at the ortho-position to one of the phosphorus atoms may, for example, be replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support.

Preferred bidentate P,P ligand moieties are derived from ligands of formula (lib)

(lib) wherein

R ¹⁰ is independently selected from linear Ci-C4-alkyl,

R ¹¹ is independently selected from CHR ¹⁰ 2, CR ¹⁰ 3, C3-Cio-cycloalkyl, and optionally alkylated aryl having 6 to 18 carbon atoms,

X is independently selected from C-H, C-CH3, and N, and

A ² together with the moieties X to which it is bound and the interjacent carbon atoms forms a 5- to 7-membered cyclic substructure.

R ¹⁰ is preferably independently selected from Ci-C6-alkyl and C3-C7-cycloalkyl and R ¹¹

R ¹⁰ may, for example, be independently selected from linear Ci-C4-alkyl, in particular from linear Ci-C2-alkyl.

R ¹¹ is preferably independently selected from CHR ¹⁰ 2, CR ¹⁰ 3, and Cs-Cs-cycloalkyl A ² is preferably a -CH=CH- bridge.

X is preferably CH.

In preferred ligand moieties derived from ligands of formula (lib), a hydrogen atom at a phosphorus bound carbon atom is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid sup- port. Alternatively, an aromatic hydrogen at the ortho-position to one of the phosphorus atoms may, for example, be replaced by the bond by which the ligand moiety is cova- lently immobilized via an optional linking and/or anchoring group on the solid support. Preferred bidentate P,P ligand moieties are derived from ligands of formula (lie)

(lie) wherein

R ¹³ and R ¹⁴ are independently selected from C3-Cio-cycloalkyl, and

_R 15 is H, O-d-Ce-alkyl, or both R ¹⁵ together constitute a -CH=CH- bridge. R ¹⁵ is preferably H or OCH3 and most preferably H.

In preferred ligand moieties derived from ligands of formula (lie), a hydrogen atom at a phosphorus bound carbon atom is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid sup- port. Alternatively, an aromatic hydrogen at the ortho-position to one of the phosphorus atoms may, for example, be replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support.

Preferred bidentate P,P ligand moieties are derived from ligands of formula (lid)

_R 16 _R 17 _P _( _{C R} 18 _R 19) _e _p _R 16 _R 17

(lid)

wherein

R ¹⁶ and R ¹⁷ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, individual hydrogen at- oms may independently be replaced by CI, Br, I, or F, and any two resi- dues bound to the same phosphorus atom may be covalently bound to one another,

e is 1 , 2, 3, 4, or 5, preferably 2, 3, or 4,

R ¹⁸ is independently selected from H , C-i-Cs-alkyl, d-Cs-alkoxy, C3-C10- cycloalkyl, C3-Cio-cycloalkoxy, C6-Cio-aryl, and C6-Cio-aryloxy, and

R ¹⁹ is independently selected from H , C-i-Cs-alkyl, C3-Cio-cycloalkyl, and C6-

Preferably, (CR ¹⁸ R ¹⁹ ) _e is -CH2-CH2-, -CH ₂ -CH ₂ -CH ₂ -, or -CH ₂ -CH ₂ -CH ₂ -CH ₂ -.

R ¹⁶ and R ¹⁷ are preferably independently Ci-Ci ₂ -alkyl, C3-Ci ₂ -cycloalkyl, or C3-Ci4-aryl, wherein C3-Ci ₂ -cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, Ci-Cs-alkyl and Ci-C4-alkoxy. R ¹⁶ and R ¹⁷ are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl)propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2-methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 - undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcy- clohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chlorophenyl or anisyl.

In preferred ligand moieties derived from ligands of formula (lid), a hydrogen atom at a phosphorus bound carbon atom is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support. Alternatively, in case of an aryl substituted phosphorus atom, an aromatic hydrogen at the ortho-position to one of the phosphorus atoms may, for example, be replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support. In a particularly preferred process of the invention, the ligand moiety is derived from 1 ,2-bis(di-tert-butylphosphino)ethane, 1 ,2-bis(diisopropylphosphino)ethane, 1 ,3- bis(diisopropylphosphino)propane, 1 ,4-bis(diisopropylphosphino)butane, 1 ,2-bis(tert- butylmethylphosphino)ethane, 1 ,2-bis(dicyclopentylphosphino)ethane, 1 ,3- bis(dicyclopentylphosphino)propane, 1 ,4-bis(dicyclopentylphosphino)butane, 1 ,2- bis(dicyclohexylphosphino)ethane, 1 ,3-bis(dicyclohexylphosphino)propane, 1 ,4- bis(dicyclohexylphosphino)butane,

Cy is cyclohexyl.

Most preferably, the ligand moiety is derived from 1 ,2- bis(dicyclohexylphosphino)ethane.

Suitable monodentate ligand moieties are, for example, monodentate carbene moieties that are derived from ligands of formula (I If)

_R e

(I If) wherein

R ⁶¹ and R ⁶² are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and where individual hydrogen atoms may independently be replaced by CI, Br, I, or F,

R ⁶³ and R ⁶⁴ , are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, individual hydrogen atoms may independently be replaced by CI, Br, I, or F, and both residues may be covalently bound to one another, and

R ⁶⁵ and R ⁶⁶ together are a chemical bond, or as defined for R ⁶³ and R ⁶⁴ .

R ⁶¹ and R ⁶² are preferably independently Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, or C3-Ci4-aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, d-Cs-alkyl and Ci-C4-alkoxy.

R ⁶¹ and R ⁶² are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl)propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2-methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 - undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcy- clohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chlorophenyl or anisyl. Preferably R ⁶³ , R ⁶⁴ , R ⁶⁵ and R ⁶⁶ are independently hydrogen, Ci-Ci ₂ -alkyl, or C1-C14- aryl; or R ⁶³ and R ⁶⁴ are independently hydrogen, Ci-Ci2-alkyl, or Ci-Ci4-aryl, and R ⁶⁵ and R ⁶⁶ together are a chemical bond; or R ⁶³ and R ⁶⁴ are independently hydrogen, or methyl, and R ⁶⁵ and R ⁶⁶ together are a C3-Cio-alkane-1 ,3-diyl, C3-Cio-alkane-1 ,4-diyl, or C3-Cio-alkane-1 ,3-diyl bridge; or R ⁶⁵ and R ⁶⁶ together are a chemical bond, and R ⁶³ , and R ⁶⁴ , together with the carbon atoms to which they are bound, are part of a monocyclic or bicyclic aromatic ring system. In preferred ligand moieties derived from ligands of formula (llf), a hydrogen of R ⁶¹ , R ⁶² , R ⁶³ , R ⁶⁴ , R ⁶⁵ , or R ⁶⁶ is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support. Suitable ligand moieties are, for example, bidentate and multidentate ligand moieties that comprise one or two coordinating phosphorus atoms and an additional carbon atom or hetero atom that is bound to the transition metal. Preferably, a 5-membered ring is formed, when the additional carbon atom or hetero atom binds to the transition metal, as for example with (diphenylphosphino)acetate known from the SHOP-Process or with 2-(dimethylphosphino)-N,N-dimethylethanamine. Specific bidentate ligand moieties are derived from ligands of formula (llg)

(iig)

wherein

W is phosphorus (P) or phosphite (P=0),

R ⁶² , R ⁶³ , R ⁶⁴ , R ⁶⁵ and R ⁶⁶ are each as already defined,

R ⁶⁷ and R ⁶⁸ are as defined for R ⁶³ and R ⁶⁴ , and

R ⁶⁹ and R ⁷⁰ are as defined for R ⁶³ and R ⁶⁴ .

Preferably R ⁶³ , R ⁶⁴ , R ⁶⁵ and R ⁶⁶ are independently hydrogen, Ci-Ci2-alkyl, or C1-C14- aryl; or R ⁶³ and R ⁶⁴ are independently hydrogen, Ci-Ci2-alkyl, or Ci-Ci4-aryl, and R ⁶⁵ and R ⁶⁶ together are a chemical bond; or R ⁶³ and R ⁶⁴ are independently hydrogen, or methyl, and R ⁶⁵ and R ⁶⁶ together are a C ₃ -Cio-alkane-1 ,3-diyl, C ₃ -Cio-alkane-1 ,4-diyl, or C3-Cio-alkane-1 ,3-diyl bridge; or R ⁶⁵ and R ⁶⁶ together are a chemical bond, and R ⁶³ , and R ⁶⁴ , together with the carbon atoms to which they are bound, are part of a monocyclic or bicyclic aromatic ring system. R ⁶² , R ⁶⁷ and R ⁶⁸ are preferably independently Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, or C3-C14- aryl, wherein C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I , F, Ci-Cs-alkyl and C1-C4- alkoxy. R ⁶² , R ⁶⁷ and R ⁶⁸ are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 - butyl, 2-butyl, tert-butyl, 1 -(2-methyl) propyl, 2-(2-methyl)propyl, 1 -pentyl, 1 -(2- methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 - decyl, 1 -undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chloro- phenyl or anisyl.

In preferred ligand moieties derived from ligands of formula (llg), a hydrogen of R ⁶² , R ⁶³ , R ⁶⁴ , R ⁶⁵ , R ⁶⁶ , R ⁶⁷ , R ⁶⁸ , R ⁶⁹ , or R ⁷⁰ is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support.

The ligand moiety may also be a bidentate or multidentate ligand moiety that comprises one or two coordinating nitrogen atoms and an additional carbon atom that is bound to the transition metal. Preferably, a 5-membered ring is formed, when the additional carbon atom binds to the transition metal, as for example with 2-phenylpyridine or 6- phenyl-2,2'-bipyridine. Suitable tridentate ligand moieties are, for example, derived from ligands of formula (llh)

_R 16 _R 17 _P .( _{C R} 18 _R 19) _v .p _R 16.( _{C R} 18 _R 19) _w .p _R 16 _R 17 (llh) wherein

R ¹⁶ , R ¹⁷ , R ¹⁸ , and R ¹⁹ are each as already defined, and

v and w are independently 1 , 2, 3, 4, or 5, preferably 2, 3, or 4.

Exemplary tridentate ligands are ((methylphosphinediyl)bis-

(methylene))bis(dimethylphosphine), ((ethylphosphindiyl)bis(methylene))bis(diethyl- phosphine), and ((methylphosphinediyl)bis(methylene))bis(diphenylphosphine). In preferred ligand moieties derived from ligands of formula (llh), a hydrogen atom at a phosphorus bound carbon atom is replaced by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support. Alternatively, in case of an aryl substituted phosphorus atom, an aromatic hydrogen at the ortho-position to one of the phosphorus atoms may, for example, be re- placed by the bond by which the ligand moiety is covalently immobilized via an optional linking and/or anchoring group on the solid support.

In addition, at least one equivalent of the base may itself coordinate to the metal of the transition metal complex.

In addition to the above-described ligand moieties, the transition metal complex may also have at least one further ligand selected from halides, amines, amides, oxides, phosphides, carboxylates, acetylacetonate, aryl- or alkylsulfonates, hydride, CO, ole- fins, dienes, cycloolefins, nitriles, aromatics and heteroaromatics, ethers, PF3, phos- pholes, and mono-, di- and polydentate phosphinite, phosphonite, phosphoramidite and phosphite ligands.

Any optional base and/or further ligand can be displaced when the alkene and carbon dioxide are reacted.

Preferably, the carboxylation catalyst comprises structural units of the general formula (IVe)

(IVe) wherein

M is the transition metal,

L' is a ligand,

n is 0, 1 , or 2,

A is a bond or a linking moiety,

G is an anchoring group,

k is 0 or 1 ,

R ¹⁶ and R ¹⁷ are independently Ci-Ci2-alkyl, C3-Ci2-cycloalkyl, or C3-Ci4-aryl, wherein

C3-Ci2-cycloalkyl and C3-Ci4-aryl are unsubstituted or substituted with 1 , 2, 3, or 4 substituents independently selected from CI, Br, I, F, C-i-Cs- alkyl and Ci-C4-alkoxy, and

* is the site of attachment to the solid support. R ¹⁶ and R ¹⁷ are most preferably independently methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl)propyl, 2-(2-methyl) propyl, 1 -pentyl, 1 -(2-methyl)pentyl, 1 -hexyl, 1 -(2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl)heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 - undecyl, 1 -dodecyl, adamantyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcy- clohexyl, cycloheptyl, cyclooctyl, norbornyl, phenyl, napthyl, tolyl, xylyl, chlorophenyl or anisyl.

The transition metal complex may, for example, be obtained from the support bound ligand moiety and the transition metal or from the support bound ligand moiety and a transition metal source comprising the transition metal at oxidation state 0. Alternative- ly, the transition metal complex may for example be obtained by reducing a salt of the transition metal with a reducing agent, e.g. hb, Mg, Na or Zn.

Useful transition metal sources and salts are commercially available and include, for example MX2, MX3, where X is selected from halide, pseudohalide, carboxylate, alkox- ide, carbonate, sulfate, nitrate, hydroxide, acetylacetonate, cyclopentadiene, and the corresponding adducts with solvents such as ethers, DMSO, or water, and M is the active metal of the transition metal complex (e.g. [M(/>cymene)Cl2]2, [M(benzene)Cl2]n, [M(COD) ₂ ], [M(CDT)], [M(C ₂ H ₄ )3], [MCI ₂ xH ₂ 0], [MCI ₃ xH ₂ 0], [M(acetylacetonate)i _-3 ], [M(DMSO) ₄ Cl2]). Other useful transition metal sources are metallalactones. These metallalactones do preferably comprise a ligand selected from diamines and phospho- amines.

It may happen that part of the carboxylation catalyst is deactivated by oxidation of the active metal. The deactivation reduces the overall efficiency of the process. Preferably a reducing agent is added. Apparently, the reducing agent reactivates the deactivated carboxylation catalyst by a reduction of the oxidized active metal. Thus, the alkene and carbon dioxide are preferably reacted in the presence of a reducing agent. Any reducing agent which is capable of reducing the deactivated carboxylation catalyst is suitable as the reducing agent. Preferable reducing agents are H2, Mg, Na and Zn.

The reaction medium preferably comprises 0.1 to 20000 ppm by weight, preferably 1 to 1000 ppm by weight, in particular 5 to 500 ppm by weight of transition metal, based on the total weight of the reaction medium. Any base that is capable of converting the metallalactone into an ^-ethylenically unsaturated carboxylic acid salt that may be associated to the transition metal is suited as the base in the process according to the invention. In particular, any base that is capable of deprotonating the metallalactone under the conditions at which the alkene and carbon dioxide are reacted is suited as the base in the process according to the invention.

Although it is possible to isolate the metallalactone from the reaction mixture and to treat the isolated metallalactone with the base, it is generally preferred to carry out the reaction as a one-pot reaction. Thus, the base may be present in the reaction medium while the alkene and carbon dioxide are reacted, or the base may be added afterwards to the reaction medium. Certain bases, in particular nucleophilic bases, can react with carbon dioxide to form fairly stable adducts and the base is not available for the cleavage of the metallalactone. In these cases, the carbon dioxide pressure should be re- lieved before the base is added. Non-nucleophilic bases are largely unreactive towards carbon dioxide and can be included in the initial reaction medium or added to the reaction medium without prior carbon dioxide pressure relief.

The base may, for example, be an anion base. Preferably, the anion base comprises a metal cation. The metal cation is preferably selected from alkali metals and alkaline earth metals.

The base is for example selected from hydrides, amides, alkoxides, and aryloxides, preferably from alkali metal or alkaline earth metal hydrides, amides, alkoxides, and aryloxides.

Suitable alkali metal or alkaline earth metal hydrides are, for example, lithium hydride, sodium hydride, potassium hydride, magnesium hydride, and calcium hydride. Suitable alkali metal or alkaline earth metal amides are, for example, LiNMe2, LiNEt ₂ , LiN(iPr) ₂ , NaNMe ₂ , NaNEt ₂ , NaN(iPr) ₂ , KNMe ₂ , KNEt ₂ , KN(iPr) ₂ , (Me = Methyl; Et = Ethyl; iPr = Isopropyl). The suitable amides also include silicon-containing amides such as sodium hexamethyldisilazide (NaHMDS), potassium hexamethyldisilazide (KHMDS) or lithium hexamethyldisilazide (LiHMDS).

Suitable alkali metal or alkaline earth metal alkoxides derive from alcohols of the formula R ¹⁰⁰ OH. Suitable R ¹⁰⁰ residues are branched or unbranched, acyclic or cyclic alkyl residues having 1 -16 carbon atoms, preferably 1 -12 carbon atoms, which are unsubsti- tuted or wherein individual carbon atoms may each independently also be replaced by a heteroatom selected from the group of O and >N.

Exemplary R ¹⁰⁰ residues are benzyl, methyl, ethyl, 1 -propyl, 2-propyl, 1 -butyl, 2-butyl, tert-butyl, 1 -(2-methyl)propyl, 1 -(2-methyl)butyl, 1 -pentyl, 1 -(2-methyl)pentyl, 1 -hexyl, 1 - (2-ethyl)hexyl, 1 -heptyl, 1 -(2-propyl) heptyl, 1 -octyl, 1 -nonyl, 1 -decyl, 1 -undecyl, 1 - dodecyl, C3-Cio-cycloalkyl which is unsubstituted or may bear a Ci-C4-alkyl group, for example cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl.

Preferred R ¹⁰⁰ residues are secondary or tertiary residues. The terms "secondary" or "tertiary" refer to the branching of the carbon atom bound to the hydroxyl group of R ¹⁰⁰ OH. Exemplary secondary or tertiary R ¹⁰⁰ residues are 2-propyl, 2-butyl, tert-butyl, cyclopentyl, methylcyclopentyl, cyclohexyl, methylcyclohexyl, cycloheptyl, cyclooctyl.

Particularly preferred R ¹⁰⁰ residues are tertiary residues, i.e. tert-butyl.

Preferable alkali metal or alkaline earth metal alkoxides are sodium methoxide, sodium ethoxide, sodium isopropoxide, sodium tert-butoxide, and sodium isobutoxide. In the case the base is an alkoxide, the alcohol from which the alkoxide is obtainable by deprotonation, may serve as the solvent.

Sodium tert-butoxide is a preferred base. Suitable aryloxides are, for example phenolates and naphtholates. The aryloxide may, for example, be an aryloxide that corres onds to the general formula (I)

(I) wherein

R is selected from F, CI, Br, I, Ci-Ci6-alkyl, C3-Ci6-cycloalkyl, and Ci-Ci6-fluoroalkyl, and two vicinal R may constitute a Cs-Cs-hydrocarbylene bridge that is optionally substituted by one to four substituents which are independently selected from F, CI, Br, I, Ci-Ci6-alkyl, C3-Ci6-cycloalkyl, and Ci-Ci6-fluoroalkyl, and

q is an integer selected from 1 to 5, wherein at most two R are F.

For example, the Cs-Cs-hydrocarbylene bridge is an unsaturated C4-hydrocarbylene bridge, preferably with two conjugated double bonds. When the C4-hydrocarbylene bridge has two conjugated double bonds, the aryloxide of formula (I) is a naphthylox- ide. The C4-hydrocarbylene bridge is optionally substituted by one to four substituents which are independently selected from F, CI, Br, I, Ci-Ci6-alkyl, C3-Ci6-cycloalkyl, and Ci-Ci6-fluoroalkyl. The aryloxide may, for example, correspond to one of the following general formulae (la-1 ), (la-2), and (la-3)

(la-1 ) (la-2) (la-3) wherein

x is 0, 1 , or 2,

R ² is methyl, and

R ³ is independently Ci-Ci6-alkyl or C3-Ci6-cycloalkyl.

Among these, the aryloxides that correspond to the formulae (la-2) and (la-3) are preferred, x is preferably 1 or 2 in formulae (la-2) and (la-3).

F is preferably ortho or meta to the oxygen (O- substituent) in the aryloxides that corre- spond to formula (la-2). Aryloxide that corresponds to formula (la-2) with F being ortho to O ^" , and x being 1 or 2, preferably 1 , is particularly preferred.

The aryloxide is preferably an alkali metal or alkaline earth metal aryloxide. Preferred alkali metal cations of the alkali metal aryloxide are Na ⁺ , Li ⁺ , and K ⁺ . Preferred alkaline earth metal cations of the alkaline earth metal aryloxide are Mg ²⁺ and Ca ²⁺ . Most preferably, the aryloxide is a sodium aryloxide.

The aryloxide may, for example, be selected from sodium 2-fluorophenolate, sodium 3- fluorophenolate, sodium 4-fluorophenolate, sodium 2,6-difluorophenolate, sodium 2,4- difluorophenolate, sodium 2-chlorophenolate, sodium 3-chlorophenolate, sodium 4- chlorophenolate, sodium 2-methylphenolate, sodium 2,6-dimethylphenolate, and sodium 1 -naphtholate. Sodium 2-fluorophenolate, sodium 3-fluorophenolate, sodium 2- chlorophenolate, and sodium 3-chlorophenolate are particularly preferred.

The aryloxide can be added in solid form or as a solution.

The aryloxide is consumed stoichiometrically when the alkene and carbon dioxide are reacted to obtain the <¾e-ethylenically unsaturated carboxylic acid salt. The aryloxide is protonated such that its conjugate acid, an arylhydroxide, is obtained as a byproduct. Quantitative consumption of the aryloxide can be prevented by reacting the arylhydroxide with an alkaline material which is capable of deprotonating the arylhydroxide such that the aryloxide is recycled. Accordingly, the process of the invention preferably comprises regenerating the aryloxide by adding an alkaline material.

The amount of aryloxide used in the process according to the invention is generally 5 to 95% by weight, preferably 20 to 60% by weight, and most preferably 5 to 15 % by weight, based on the overall reaction medium in the reactor. It is possible to use the aryloxide in substoichiometric amounts based on the carboxylation catalyst. Even when substoichiometric amounts of aryloxide are used, it is possible to obtain <¾e-ethylenically unsaturated carboxylic acid salt in excess as based on the catalyst concentration, if the aryloxide is regenerated by addition of the alkaline material.

If an alkaline material is used that is capable of regenerating the aryloxide under the conditions at which the alkene and carbon dioxide are reacted, the alkaline material may be present in the reaction medium while the alkene and carbon dioxide are reacted to the <¾e-ethylenically unsaturated carboxylic acid salt. Such alkaline material is for example added into the carboxylation reactor while the alkene and carbon dioxide are reacted.

If the alkaline material is added outside of the carboxylation reactor, i.e. at low carbon dioxide partial pressure, alkaline materials that are inactivated at the conditions of the reaction between alkene and carbon dioxide, i.e. at high carbon dioxide partial pressure, may be used. These alkaline materials include alkali metal or alkaline earth metal hydroxides, oxides and alkoxides. The alkaline material is, for example, selected from elemental alkali metal, alkali metal or alkaline earth metal hydroxides, carbonates, hydrogencarbonates, oxides, phosphides, phosphates, silanolates, alkyls, and aryls. Suitable alkali metal and alkaline earth metal hydroxides are, for example, sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide.

Suitable alkali metal and alkaline earth metal carbonates are, for example, lithium carbonate, sodium carbonate, potassium carbonate and calcium carbonate.

Suitable alkali metal hydrogencarbonates are, for example, sodium hydrogencarbonate or potassium hydrogencarbonate.

Suitable alkali metal and alkaline earth metal oxides are, for example, lithium oxide, sodium oxide, calcium oxide and magnesium oxide. Preference is given to sodium hydroxide.

Suitable alkali metal or alkaline earth metal phosphides are, for example, those of the formula M ² PR ¹⁰¹ 2 in which M ² is an alkali metal or an equivalent of an alkaline earth metal, and R ¹⁰¹ is Ci-i ₂ -alkyl or C ₆ -io-aryl, for example KPPh ₂ or Na PPh ₂ (Ph = Phenyl).

Suitable alkali metal or alkaline earth metal silanolates are, for example, those of the formula M ² OSi(Ci-4-Alkyl)3 in which M ² is an alkali metal or an equivalent of an alkaline earth metal, for example NaOSiMe3.

Suitable alkali metal or alkaline earth metal alkyls or aryls are, for example, lithium alkyl and lithium aryl compounds, such as methyllithium, n-butyllithium, sec-butyllithium, tert- butyllithium, phenyllithium, where the benzene ring may bear substituents at any position (e.g. OCH3, CH2lMMe2, CONR2), cyclohexyllithium, where the cyclohexyl ring may comprise heteroatoms (e.g. O, N, S), ethyllithium, lithium pentadienyl, lithium 2-furanyl, lithium 2-thiophenyl, lithium ethynyl. Also suitable are sodium alkyl and sodium aryl compounds, such as sodium cyclopentadienyl.

The suitable alkaline earth metal alkyls and aryls include magnesium alkyl and magne- sium aryl compounds (Grignard reagents) of the general formula R ¹⁰² MgX, where R ¹⁰² may be one of the alkyl and aryl residues listed above for the lithium alkyl and lithium aryl compounds and X may be F, CI, Br, I. Suitable alkaline materials are also alkali metals, in particular sodium. The deprotona- tion of the arylhydroxide is then coupled with a redox reaction. The alkali metal is oxidized to the alkali metal cation and the oxygen-bound proton of the arylhydroxide is reduced to hydrogen.

Some of the aforementioned bases, i.e. alkali metal or alkaline earth metal hydrides, amides, and alkoxides, are also capable of regenerating the aryloxide by deprotonating the arylhydroxide. Suitable alkaline materials are thus also the aforementioned alkali metal or alkaline earth metal hydride, amide, and alkoxide bases.

The process of the invention is preferably carried out in the presence of alkali metal or alkaline earth metal cations. Preferred alkali metal cations are Na ⁺ , Li ⁺ , and K ⁺ . Preferred alkaline earth metal cations are Mg ²⁺ and Ca ²⁺ . The process of the invention is most preferably carried out in the presence of sodium cations.

In a particularly preferred embodiment of the process, the base is an organic base being homogeneously dissolved in the reaction medium in which the alkene and carbon dioxide are reacted, and the reaction medium is in contact with a heterogeneous alkalinity reservoir.

Preferably, the organic base is aprotic. Aprotic means that the organic base is not capable of acting as a proton donor under the conditions of the reaction of the alkene with carbon dioxide. In particular, the organic base does not comprise hydrogen atoms bound to heteroatoms such as N, O, S, or P.

The organic base is preferably selected from tertiary amines, phosphazene bases, and tertiary phosphines.

Preferred tertiary amines correspond to the general formula (Ilia)

NR ²⁶ R ²⁷ R ²⁸ (Ilia) in which R ²⁶ to R ²⁸ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and two or all three residues may be covalently bound to one another. Preferably, R ²⁶ to R ²⁸ are independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where two or all three residues may be covalently bound to one another.

Preferred phosphazene bases correspond to the general formula (1Mb),

(1 M b)

R ²⁹ is an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-,

D ¹ is selected from NR ³⁰ ₂ , and N=P(NR ³¹ ₂ ) ₃ ,

D ² is selected from NR ³⁰ ₂ , and N=P(NR ³¹ ₂ ) ₃ ,

D ³ is selected from NR ³⁰ ₂ , and N=P(NR ³¹ ₂ ) ₃ ,

R ³⁰ is independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may independently be replaced by a hetero group selected from the group of -O- and >N-, and any two residues R ³⁰ may be covalently bound to one another, and

R ³¹ is independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, where individual carbon atoms may each independently be replaced by a hetero group selected from the group of -O- and >N-, and any two residues R ³¹ that are part of the same D ¹ , D ² , or D ³ , may be covalently bound to one another.

R ²⁹ is preferably an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 16 carbon atoms, for example an unbranched or branched aliphatic residue having 1 to 16 carbon atoms.

R ³⁰ is preferably independently an unbranched or branched, acyclic or cyclic, aliphatic, araliphatic or aromatic residue having 1 to 5 carbon atoms, where any two residues R ³⁰ may be covalently bound to one another. R ³⁰ is, for example, methyl, ethyl, or propyl, two resdiues R ³⁰ form a 1 ,4-butylene, or 1 ,5-pentylene bridge.

R ³¹ is preferably independently an unbranched aliphatic residue having 1 to 5 carbon atoms.

The organic base is, for example, selected from triethylamine, trioctylamine, N,N- dimethylanilin, Ν,Ν-diethylanilin, 4-(dimethylamino)pyridine, 1 ,8- diazabicyclo[5.4.0]undec-7-ene,

The reaction medium may comprise, for example, 1 to 100000 ppm by weight, preferably 5 to 25000 ppm by weight, in particular 25 to 10000 ppm by weight of the organic base, based on the total weight of the reaction medium. Any material that is capable of converting the conjugate acid of the organic base into the organic base and thereby releases alkali metal cations or alkaline earth metal cations, preferably sodium, lithium or potassium cations, in particular sodium cations may serve as alkalinity reservoir. This does not mean that the conversion of conjugate acid of the organic base into the organic base does necessarily occur in the process accord- ing to the invention. When the alkalinity reservoir is selected from alkali metal or alkaline earth metal anion bases, converting the conjugate acid of the organic base into the organic base involves the transfer of a proton from the conjugate acid of the organic base to the anion of the alkali metal or alkaline earth metal anion base. When the proton is transferred to the anion of the anion base, the alkali metal or alkaline earth metal anion is released.

When the alkalinity reservoir is selected from elemental alkali metals, converting the conjugate acid of the organic base into the organic base goes in hand with the reduc- tion of the proton from the conjugate acid to hb, the oxidation of the elemental alkali metal to the alkali metal cation, and release of the alkali metal cation.

The alkalinity reservoir may be solid or liquid under the conditions of the reaction of the alkene and carbon dioxide. The alkalinity reservoir is preferably solid under the condi- tions of the reaction of the alkene and carbon dioxide. The alkalinity reservoir is preferably dispersed in the reaction medium. It may, for example, be present in the form of a discontinuos liquid or solid phase that is dispersed in the reaction medium.

Preferably, the alkalinity reservoir is selected from elemental alkali metals, alkali metal or alkaline earth metal anion bases, and their mixtures.

The elemental alkali metal of the heterogeneous alkalinity reservoir may, for example, be sodium, lithium or potassium. Sodium is preferred. A suitable alkali metal or alkaline earth metal anion base of the heterogeneous alkalinity reservoir is, for example, selected from alkali metal hydrides, alkaline earth metal hydrides, alkali metal amides, alkaline earth metal amides, alkali metal phosphides, alkaline earth metal phosphides, and their mixtures. Alkali metal hydrides, alkaline earth metal hydrides, alkali metal phosphides, alkaline earth metal phosphides, and their mixtures are preferred. Alkali metal hydrides, and alkaline earth metal hydrides are particularly preferred.

The cation of the alkali metal or alkaline earth metal anion base of the heterogeneous alkalinity reservoir may, for example, be selected from sodium, lithium, potassium, magnesium, and calcium. Sodium, lithium and potassium, are preferred. Sodium is particularly preferred.

Particularly preferred anion bases of the heterogeneous alkalinity reservoir are sodium hydride, potassium hydride and lithium hydride. The most preferred alkalinity reservoir is sodium hydride.

It is possible to use the organic base in substoichiometric amounts based on the carboxylation catalyst.

The molar ratio of organic base to alkali metal or alkaline earth metal of the heterogeneous alkalinity reservoir is, for example, between 1 :1 and 1 :1000, preferably between 1 :1 and 1 :500, and most preferably between 1 :1 and 1 :100.

The reaction of the alkene and carbon dioxide is preferably carried out in an aprotic organic solvent. Suitable aprotic organic solvents are in principle those which (i) are chemically inert with regard to the carboxylation of the alkene, and (ii) in which the base has good solubility. Useful aprotic organic solvents are therefore in principle chemically inert, nonpolar solvents, for instance aliphatic, aromatic or araliphatic hydrocarbons, for example octane and higher alkanes, benzene, toluene, xylene, and chlo- robenzene. The reaction medium may, for example, comprise an organic solvent selected from aromatic hydrocarbons, halogenated aromatic hydrocarbons, alkylated aromatic hydrocarbons, alkanes, ethers, and mixtures thereof. Examples of suitable ethers are dimethylether, diethylether, di-tert-butylether, di-n-butylether, tetrahydrofuran and 2-methyl-tetrahydrofuran.

The reactors used may in principle be all reactors which are suitable in principle for gas/liquid reactions or liquid/liquid reactions at the given temperature and the given pressure. Suitable standard reactors for liquid-liquid reaction systems are specified, for example, in K. D. Henkel, "Reactor Types and Their Industrial Application", in

Ullmann ^' s Encyclopedia of Industrial Chemistry 2005, Wiley VCH Verlag GmbH & Co KGaA, DOI: 10.1002/14356007.b04_087, chapter 3.3 "Reactors for gas-liquid reactions". Examples include stirred tank reactors, tubular reactors or bubble columns.

The process may be performed as a continuous process or as a discontinuous process. In the discontinuous process, the ligand moiety being covalently bound to the solid support, the transition metal which may, for example, be in the form of the transition metal source, the base, carbon dioxide and the alkene are given into the reactor. Preferably, gaseous carbon dioxide and gaseous alkene are passed into the reactor at the desired pressure. After the reaction has slowed down, the pressure may be reduced. The process may, for example, be performed at pressures between 1 and 300 bar, preferably between 1 and 200 bar, in particular between 1 and 150 bar. The process may for example be performed at temperatures between -20 and 300 °C, preferably between 20 and 250 °C, in particular between 40 and 200 °C or between 50 and 180°C, most preferably between 60 and 170 °C.

CO2, the alkene, the base (i.e. the organic base), and optionally the heterogeneous alkalinity reservoir can be fed to the reaction medium either together or spatially separated. Such a spatial separation can be accomplished, for example in a stirred tank, in a simple manner by means of two or more separate inlets. When more than one tank is used, for example, there may be different media charges in different tanks. Separation of the addition of the CO2 and alkene reactants in terms of time is also possible in the process according to the invention. Such a time separation can be accomplished, for example, in a stirred tank by staggering the charging with the reactants. In the case of use of flow tubes or apparatus of a similar kind, such charging can be effected, for example, at different sites in the flow tube; such a variation of the addition sites is an elegant way of adding the reactants as a function of residence time.

In order to achieve good mixing of the reactants and of the medium comprising the carboxylation catalyst and the base, suitable apparatuses can be used. Such apparatuses may be mechanical stirrer apparatuses with one or more stirrers, with or without baffles, packed or nonpacked bubble columns, packed or nonpacked flow tubes with or without static mixers, or other useful apparatuses known to those skilled in the art for these process steps. The use of baffles and delay structures is explicitly included in the process according to the invention.

The reaction medium comprising the crude <¾e-ethylenically unsaturated carboxylic acid salt can be processed with little effort to obtain the carboxylic acid derivative at high purity level.

After the reaction, a polar solvent can be added to the reaction medium and the carboxylation catalyst is then separated from the reaction medium by solid-liquid phase separation, i.e. by filtration. The polar solvent is preferably water. The carboxylation catalyst obtained from the solid-liquid phase separation, i.e. filtration, can be used again, i.e. after optional drying in a stream of inert gas, as a carboxylation catalyst in the process according to the invention. A liquid comprising an organic phase and a polar phase, i.e. aqueous phase, is obtained after the solid-liquid phase separation. The phases are preferably separated by liquid-liquid-phase separation. The

<¾e-ethylenically unsaturated carboxylic acid salt can be isolated from the polar phase, i.e. aqueous phase, by evaporating the polar solvent. The organic phase can be recycled into the process according to the invention.

Alternatively, a solid comprising the carboxylation catalyst and <¾e-ethylenically unsatu- rated carboxylic acid salt is separated from the reaction medium by a first solid-liquid phase separation and a polar solvent, preferably water, is then added to the solid. The <¾e-ethylenically unsaturated carboxylic acid salt is dissolved by the polar solvent. The catalyst can be separated from the polar solvent by a second solid-liquid phase separation, i.e filtration. The carboxylation catalyst obtained from the second solid-liquid phase separation can be used again, i.e. after optional drying in a stream of inert gas, as a carboxylation catalyst in the process according to the invention. The liquid obtained from the first solid-liquid phase separation is an organic phase. The organic phase can be recycled into the process according to the invention. Traces of water comprised by any of the above organic phases can be removed by contacting the organic phase with a drying agent. Preferably, the organic phase is recirculated to the carboxylation reactor via a column that is filled with drying agent. If the base is enriched in the organic phase, the base is efficiently recycled with the organic phase. If the base is organic, lipophilic and uncharged, the recycling of the base is most efficient, as no or only a small part of the base is transferred into the polar phase. On the other hand, water soluble bases are recycled from the polar phase, i.e. by fractional distillation. As no carboxylation catalyst is comprised by the organic phase, no undesired absorption of catalyst occurs when the organic phase is contacted with the drying agent.

The invention is illustrated in detail by the examples which follow.

The following abbreviations are used: dcpe 1 ,2-bis(dicyclohexylphosphino)ethane

divinylbenzene

HCI hydrochloric acid

LiPCy ₂ lithium dicyclohexylphosphide

THF tetrahydrofuran

TON turnover number with respect to transition metal

Heterogeneous catalysts with a transition metal complex being covalently immobilized on a solid support were tested in the process according to the invention. Example 1 :

Preparation of a solid support functionalized with 3-bromopropyl moieties: A suspension of silica with average pore diameter: 6 nm, specific surface area 1 164 m ² /g, pore volume 1.25 mL/g, -OH content: 2.8 mmol/g (6 g) and (3-bromopropyl)trimethoxysilane (3.09 mL, 16 mmol) in toluene (100 mL) was stirred at 25 °C for one hour. A solution of ethanol (4.3 mL), water (2 mL) and HCI (80 pL) was added and the reaction mixture was stirred under reflux for 5 hours. The reaction mixture was cooled and further stirred at 25 °C. The product was filtered, washed with methanol, pentane, and THF (3 x 50 mL each), and dried at 50 °C in vacuo for 16 hours. Other silica may be used as well, e.g. Cariact Q-20C, average pore diameter: 20 nm, specific surface area 140 m ² /g, pore volume 0.8 mL/g.

The functionalization may be repeated several times in order to achieve higher degrees of functionalization.

Preparation of protected ligand: Borane dimethyl sulfide complex (26 mL, 2 M solution in THF, 1 .1 eq) was added dropwise under argon to a solution of dcpe (10 g, 23.66 mmol) in anhydrous THF (150 mL) at 25 °C and was stirred for 16 hours. Excess borane dimethyl sulfide complex was removed with argon. The solvent was removed in vacuo. Recrystallization from toluene and drying in vacuo yielded 9.24 g of dcpe*2BH3 complex as a white powder.

Preparation of a first solid support with covalently immobilized dcpe: To a solution of the protected ligand (1.667 g dcpex2BH ₃ , 3.83 mmol) in THF (14 mL) tert-butyllithium (5.6 mL, 2.5 equiv., 1 .7 M solution in pentane) was added dropwise for 2 hours at 0 °C. A suspension of the solid support functionalized with 3-bromopropyl moieties (10 g, 1 .189 mmol Br/g silica substrate) in pentane (40 mL) was added. The reaction mixture was further stirred at 0 °C for 72 hours. The yellowish product was filtered, washed three times with THF (50 mL) and dried in vacuo for 24 hours. The functionalized silica was then stirred in a flask at 1 10 °C for 3 hours with an excess of morpholine. The product was then washed under argon with THF (4 x 20 mL) and dried in vacuo.

Example 2:

The preparation of silica functionalized with 4-oxa-6,7-dichloroheptyl moieties was car- ried out as described in M. Cai, Y. Huang, H. Zhao, C. Song, J. Organomet. Chem. 2003, 682, 20-25 under "3. 1 Preparation of silica-supported bidentate arsine ligand CSi'-2As)". Preparation of a second solid support with covalently immobilized dcpe: A solution of LiPCy2 (204.22 mg, 1 mmol-) in THF (15 mL) was added dropwise to a suspension of the 4-oxa-6,7-dichloroheptyl functionalized silica (5 g) in THF (15 mL) at -20 °C. The reaction mixture was slowly warmed to 25 °C and stirred for 72 hours. The solids were filtered, dried, washed with THF (3 x 50 mL) and dried in vacuo.

Example 3:

Preparation of protected ligand: Borane dimethyl sulfide complex (26 mL, 2 M solution in THF, 1 .1 eq) was added dropwise under argon to a solution of dcpe (10 g, 23.66 mmol) in anhydrous THF (150 mL) at 25 °C and was stirred for 16 hours. Excess borane dimethyl sulfide complex was removed with argon. The solvent was removed in vacuo. Recrystallization from toluene and drying in vacuo yielded 9.24 g of dcpe*2BH3 complex as a white powder. Preparation of a polystyrene support with covalently immobilized dcpe: To a solution of the protected ligand (518 mg dcpe*2BH3, 1.15 mmol) in THF (4 mL) tert-butyllithium (1 .69 mL, 2.5 equiv., 1 .7 M solution in pentane) was added dropwise for 2 hours at 0 °C. A suspension of 2.5 g polystyrene (functionalized with 2-bromoethyl functional group, Sigma Aldrich, crosslinked with 1 % DVB, particle size: 160-200 μτη, Br loading: 0.9 mmol/g, pre-dried at 0°C in vacuo overnight) in pentane (5 mL) was added at -75 °C. The reaction mixture was stirred at -75 °C for 6 hours, after which the mixture was slowly heated to 0 °C and further stirred for 90 hours. The yellowish product was filtered, washed three times with THF (50 mL) and dried in vacuo for 24 hours. The functionalized silica was then stirred in a flask at 1 10 °C for 3 hours with an excess of morpholine. The product was then washed under argon with THF (4 x 20 mL) and dried in vacuo.

Example 4:

Preparation of protected ligand: Borane dimethyl sulfide complex (26 mL, 2 M solution in THF, 1 .1 eq) was added dropwise under argon to a solution of dcpe (10 g, 23.66 mmol) in anhydrous THF (150 mL) at 25 °C and was stirred for 16 hours. Excess borane dimethyl sulfide complex was removed with argon. The solvent was removed in vacuo. Recrystallization from toluene and drying in vacuo yielded 9.24 g of dcpe*2BH3 complex as a white powder.

Preparation of a polystyrene support with covalently immobilized dcpe: To a solution of the protected ligand (518 mg dcpe*2BH3, 1.15 mmol) in THF (4 mL) tert-butyllithium (1 .69 mL, 2.5 equiv., 1 .7 M solution in pentane) was added dropwise for 2 hours at 0 °C. A suspension of the polystyrene support bromoethyl functional group (2.5 g, 0.9 mmol Br/g polystyrene substrate, previously pre-dried at 0°C in vacuo overnight) in pentane (5 mL) was added. The reaction mixture was further stirred at 0 °C for 72 hours. The yellowish product was filtered, washed three times with THF (50 mL) and dried in vacuo for 24 hours. The functionalized silica was then stirred in a flask at 1 10 °C for 3 hours with an excess of morpholine. The product was then washed under argon with THF (4 x 20 mL) and dried in vacuo.

Example 5 (use in a catalytic reaction):

An autoclave (inner volume = 160 mL) was made inert overnight (100 °C, vacuum), and then purged with ethylene until the inner atmosphere was fully replaced. 1500 mg of the solid support with covalently immobilized dcpe (loading of 1 ,2- bis(dicyclohexylphosphino)ethane = 0.0194 mmol/g) from example 3, Ni(COD)2 (0.1 mmol, 28 mg) and triethylamine (10 mmol, 101 1.9 mg) were suspended in THF (45 mL). The suspension was mixed with fine powdered NaH (10 mmol, 240 mg) and then immediately transferred under inert conditions into the autoclave at room temperature. The autoclave was pressurized with ethylene (5 bar) and CO2 (10 bars) at room temperature, heated to 100 °C and stirred at 2000 rpm. After 68 hours of reaction the autoclave was cooled to room temperature and the excess pressure was released within 10 min. To the reaction mixture a mixture of D2O -THF (15 mL/10 mL) was added drop- wise. The resulting mixture was diluted with D2O (15 mL) and the biphasic liquid was extracted with diethyl ether (2 x 20 mL). The aqueous phase was mixed with 2,2,3,3-04- 3-(trimethylsilyl)propionic acid (0.167 mmol, 28.7 mg) and analyzed by ¹ H-NMR spectroscopy. Content: 0.192 mmol sodium acrylate (TON = 0.9). Example 6 (use in a catalytic reaction):

An autoclave (inner volume = 160 mL) was made inert overnight (100 °C, vacuum), and then purged with ethylene until the inner atmosphere was fully replaced. 1200 mg of the solid support with covalently immobilized dcpe (loading of 1 ,2- bis(dicyclohexylphosphino)ethane = 0.0759 mmol/g) from example 4, (tmeda)- nickelalactone (0.1 mmol, 25 mg) and triethylamine (5 mmol, 505.95 mg) were suspended in THF (45 mL). The suspension was mixed with fine powdered NaH (5 mmol, 120 mg) and then immediately transferred under inert conditions into the autoclave at room temperature. The autoclave was pressurized with ethylene (10 bar) and CO2 (20 bars) at room temperature, heated to 100 °C and stirred at 2000 rpm. After 92 hours of reaction the autoclave was cooled to room temperature and the excess pressure was released within 10 min. To the reaction mixture a mixture of D2O -THF (15 mL/10 mL) was added dropwise. The resulting mixture was diluted with D2O (15 mL) and the biphasic liquid was extracted with diethyl ether (2 x 20 mL). The aqueous phase was mixed with 2,2,3,3-<¾-3-(trimethylsilyl)propionic acid (0.167 mmol, 28.7 mg) and analyzed by ¹ H-NMR spectroscopy. Content: 0.135 mmol sodium acrylate (TON = 0.7).

Example 7 (use in a catalytic reaction, reference example):

The example was carried out as example 6 but without immobilized dcpe (TON = 0).

Example 8 (use in a catalytic reaction):

Preparation of immobilized catalytic species (nickelalactone) ex situ: 500 mg of the solid support with covalently immobilized dcpe (loading of 1 ,2- bis(dicyclohexylphosphino)ethane = 0.0759 mmol/g) from example 4 and (tmeda)- nickelalactone (0.1 mmol, 25 mg) were suspended in THF and stirred at 25 °C for 24 hours. The solid was filtrated, washed with 3x20 mL THF, and dried in vacuo at 25 °C overnight. An autoclave (inner volume = 160 mL) was made inert overnight (100 °C, vacuum), and then purged with ethylene until the inner atmosphere was fully replaced. Prepared immobilized (dcpe)-nickelalactone and triethylamine (10 mmol, 101 1.9 mg) were suspended in THF (45 mL). The suspension was mixed with fine powdered NaH (10 mmol, 240 mg) and then immediately transferred under inert conditions into the autoclave at room temperature. The autoclave was pressurized with ethylene (10 bar) and CO2 (20 bars) at room temperature, heated to 100 °C and stirred at 2000 rpm. After 68 hours of reaction the autoclave was cooled to room temperature and the excess pressure was released within 10 min. To the reaction mixture a mixture of D2O -THF (15 mL/10 mL) was added dropwise. The resulting mixture was diluted with D2O (15 mL) and the bi- phasic liquid was extracted with diethyl ether (2 x 20 mL). The aqueous phase was mixed with 2,2,3,3-<¾-3-(trimethylsilyl)propionic acid (0.167 mmol, 28.7 mg) and analyzed by ¹ H-NMR spectroscopy. Content: 0.284 mmol sodium acrylate (TON = 1.4).

Example 9 (use in a catalytic reaction, reference example):

The example was carried out as example 8 but without immobilized dcpe (TON = 0).

Examples 5, 6 and 8 demonstrate the efficiency of the process according to the invention. Examples 7 and 9 show that no ^-ethylenically unsaturated carboxylic acid salt is obtained in the absence of the carboxylation catalyst comprising a covalently immo- bilized transition metal complex.