Conjugated dienes such as 1,3-butadiene and isoprene undergo a variety of catalytic oligomerization reactions to give cyclic or acyclic oligomers. These oligomers are valuable feed stocks for producing fine organic chemicals. For example, the dimers and trimers are utilized as intermediates for synthesizing plasticizers, flame retardants, terpenoid and sesquiterpenoid compounds of biological interest, and fragrances.

Various coordination catalyst systems based on Ni, Pd, Co, Ti, Cr, and Fe have been reported for catalyzing the oligomerization of conjugated dienes. The majority of these catalyst systems, however, have no practical utility because they have low activity and poor selectivity. The resulting oligomerization product is often a complicated mixture of cyclic and acyclic dimers, trimers, tetramers, and higher oligomers. Furthermore, some oligomerization catalyst systems also generate a certain amount of polymer in the oligomerization product mixtures.

Several Fe-based coordination catalyst systems for oligomerizing conjugated dienes are known. For example, one process for the oligomer- zation of 1,3-butadiene employs a catalyst system including iron (III) acetyl- acetonate and triethylaluminum. Another process employs a catalyst system including ironlil) acetylacetonate, triethylaluminum, and triphenylphosphine.

Yet another process employs a catalyst system comprising Fers, triphenyl- phosphine, and triethylaluminum. All of these Fe-based catalyst systems, however, have very low activity and poor selectivity, and the resulting oligomerization product is a mixture of cyclic and acyclic dimers, trimers, and higher oligomers, as well as polymer.

SUMMARY OF THE INVENTION The present invention provides a catalyst composition that is the combination of, is the reaction product of, or is formed by combining ingredients that include a halogen-containing Fe compound or an Fe- containing compound and a halogen-containing compound; a silyl phospho- nate; and an organoaluminum compound.

The present invention further includes a process for forming conjugated diene oligomers that includes oligomerizing conjugated diene monomers in the presence of a catalytically effective amount of this catalyst composition.

Advantageously, the catalyst composition of this invention has very high activity, which allows conjugated diene oligomers to be produced in very high yields with low catalyst levels after relatively short oligomerization times. In addition, since this catalyst composition is highly active even at low temperatures, the oligomerization may be carried out under very mild temp- erature conditions, thereby avoiding thermal polymerization and/or cracking or other deleterious effects. Further, the halogen-containing Fe compounds that are utilized are generally stable, inexpensive, relatively innocuous, and readily available. Furthermore, this catalyst composition is very selective.

For instance, by utilizing this catalyst, 1,3-butadiene can be converted quantitatively to acyclic dimers without the production of any other products.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The catalyst composition is formed by combining a halogen- containing Fe compound or an Fe-containing compound in combination with a halogen-containing compound; a silyl phosphonate; and an organoalum- inum compound. In addition to these ingredients, other organometallic compounds or Lewis bases that are known in the art can also be added, if desired.

Where a halogen-containing Fe compound is used, various such compounds or mixtures thereof can be employed. The Fe atom in the halogen-containing Fe compounds can be in various oxidation states

including, but not limited to, +2, +3, and +4. Ferrous compounds, where the Fe atom is in the +2 oxidation state, and ferric compounds, where the Fe atom is in the +3 oxidation state, are preferred.

Suitable halogen-containing Fe compounds include, but are not limited to, the following classes of compounds: fluorides, chlorides, bromides, iodides, oxyhalides, and mixtures thereof. Some specific exam- ples of halogen-containing Fe compounds include FeF2, FeF3, iron (ill) oxyfluoride, FeCI2, FeCl3, iron (III) oxychloride, FeBr2, FeBr3, iron (III) oxybromide, and Fel2.

Where an Fe-containing compound and a halide-containing compound are used in combination, various Fe-containing compounds or mixtures thereof can be employed. Preferably, Fe-containing compounds that are soluble in a hydrocarbon solvent such as aromatic hydrocarbons, aliphatic hydrocarbons, or cycloaliphatic hydrocarbons are employed.

Hydrocarbon-insoluble Fe-containing compounds, however, can be suspended in the oligomerization medium to form the catalytically active species and are therefore useful.

The Fe atom in the Fe-containing compounds can be in various oxidation states including, but not limited to, 0, +2, +3, and +4. Ferrous compounds and ferric compounds are preferred. Suitable Fe-containing compounds that can be utilized include, but are not limited to, the following classes of compounds: carboxylates, organophosphates, organophospho- nates, organophosphinates, (dithio) carbamates, xanthates, p-diketonates, alkoxide or aryloxides, organoiron compounds, and mixtures thereof.

Suitable iron carboxylates, where the oxidation state of the associated Fe can be either +2 or +3, include formate, acetate, (meth) acrylate, valerat, gluconate, citrate, fumarate, lactate, maleat, oxalate, 2-ethylhexanoate, neodecanoate, naphthenate, stearate, oleate, benzoate, and picolinate.

Suitable iron organophosphates, where the oxidation state of the associated Fe can be either +2 or +3, include dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, diheptyl phosphate, dioctyl phosphate, bis (1- methylheptyl) phosphate, bis (2-ethylhexyl) phosphate, didecyl phosphate,

didodecyl phosphate, dioctadecyl phosphate, dioleyl phosphate, diphenyl phosphate, bis (p-nonylphenyl) phosphate, butyl (2-ethylhexyl) phosphate, (1-methylheptyl) (2-ethylhexyl) phosphate, and (2-ethylhexyl) (p-nonyl- phenyl) phosphate.

Suitable iron organophosphonates, where the oxidation state of the associated Fe can be either +2 or +3, include butyl phosphonate, pentyl phosphonate, hexyl phosphonate, heptyl phosphonate, octyl phosphonate, (1-methylheptyl) phosphonate, (2-ethylhexyl) phosphonate, decyl phospho- nate, dodecyl phosphonate, octadecyl phosphonate, oleyl phosphonate, phenyl phosphonate, (p-nonylphenyl) phosphonate, butyl butylphosphonate, pentyl pentylphosphonate, hexyl hexylphosphonate, heptyl heptylphospho- nate, octyl octylphosphonate, (1-methylheptyl) (1-methylheptyl) phosphonate, (2-ethylhexyl) (2-ethylhexyl) phosphonate, decyl decylphosphonate, dodecyl octadecyl octadecylphosphonate, oleyl oleylphosphonate, phenyl phenyl- phosphonate, (p-nonylphenyl) (p-nonylphenyl) phosphonate, butyl (2-ethyl- hexyl) phosphonate, (2-ethylhexyl) butylphosphonate, (1-methylheptyl) (2- ethylhexyl) phosphonate, (2-ethylhexyl) (1-methylheptyl) phosphonate, (2- ethylhexyl) (p-nonylphenyl) phosphonate, and (p-nonylphenyl) (2-ethylhexyl)- phosphonate.

Suitable iron organophosphinates, where the oxidation state of the associated Fe can be either +2 or +3, include butylphosphinate, pentyl- phosphinate, hexylphosphinate, heptylphosphinate, octylphosphinate, (1- methylheptyl) phosphinate, (2-ethylhexyl) phosphinate, decylphosphinate, dodecylphosphinate, octadecylphosphinate, oleylphosphinate, phenylphos- phinate, (p-nonylphenyl) phosphinate, dibutylphosphinate, dipentylphos- phinate, dihexylphosphinate, diheptylphosphinate, dioctylphosphinate, bis (1- methylheptyl) phosphinate, bis (2-ethylhexyl) phosphinate, didecylphos- phinate, didodecylphosphinate, dioctadecylphosphinate, dioleylphosphinate, diphenylphosphinate, bis (p-nonylphenyl) phosphinate, butyl (2-ethylhexyl)- phosphinate, (1-methylheptyl) (2-ethylhexyl) phosphinate, and (2-ethylhexyl)- (p-nonylphenyl) phosphinate.

Suitable iron (dithio) carbamates, where the oxidation state of the associated Fe can be either +2 or +3, include dimethyl (dithio) carbamate, diethyl (dithio) carbamate, diisopropyl (dithio) carbamate, dibutyl (dithio)- carbamate, and dibenzyl (dithio) carbamate.

Suitable iron xanthates, where the oxidation state of the associated Fe can be either +2 or +3, include methylxanthate, ethylxanthate, isopropylxanthate, butylxanthate, and benzylxanthate.

Suitable iron p-diketonates, where the oxidation state of the associated Fe can be either +2 or +3, include acetylacetonate, trifluoro- acetylacetonate, hexafluoroacetylacetonate, benzoylacetonate, and 2,2,6,6- tetramethyl-3, 5-heptanedionate.

Suitable iron alkoxide or aryloxides, where the oxidation state of the associated Fe can be either +2 or +3, include methoxide, ethoxide, isopro- poxide, 2-ethylhexoxide, phenoxide, nonylphenoxide, and naphthoxide.

The term"organoiron compound"refers to any Fe compound containing at least one covalent Fe-C bond. Suitable organoiron compounds include bis (cyclopentadienyl) iron (ici), bis (pentamethylcyclopentadienyl)- iron (il), bis (pentadienyl) iron (II), bis (2,4-dimethylpentadienyl) iron (il), bis (allyl)- dicarbonyliron (lt), (cyclopentadienyl) (pentadienyl) iron (il), tetra (1-norbornyl)- iron (IV), (trimethylenemethane) tricarbonyliron (II), bis (butadiene) carbonyl- iron (O), butadienetricarbonyliron (O), and bis (cyclooctatetraene) iron (O).

The halogen-containing compound employed as part of the second embodiment may include various compounds or mixtures thereof that contain one or more halide ions. A combination of two or more halide ions can also be utilized. Halogen-containing compounds that are soluble in a hydrocarbon solvent are preferred. Hydrocarbon-insoluble halogen- containing compounds, however, can be suspended in the oligomerization medium to form the catalytically active species, and are therefore useful.

Suitable halogen-containing compounds include, but are not limited to, elemental halogens, mixed halogens, hydrogen halides, organic halides, inorganic halides, metallic halides, organometallic halides, and mixtures thereof. Preferred halogen-containing compounds are hydrogen halides,

metallic halides, and organometallic halides, all of which contain at least one labile halide ion.

Suitable elemental halogens include F2, C12, Br2, and 12. Specific examples of suitable mixed halogens include ICI, tBr, ICI3, and IF6.

Suitable hydrogen halides include HF, HCI, HBr, and Hl.

Suitable organic halides include t-butyl chloride, t-butyl bromides, allyl chloride, allyl bromide, benzyl chloride, benzyl bromide, chloro-di-phenyl- methane, bromo-di-phenylmethane, triphenylmethyl chloride, triphenylmethyl bromide, benzylidene chloride, benzylidene bromide, methyltrichlorosilane, phenyltrichlorosilane, dimethyidichlorosilane, diphenyidichlorosilane, trimethylchlorosilane, benzoyl chloride, benzoyl bromide, propionyl chloride, propionyl bromide, methyl chloroformate, and methyl bromoformate.

Suitable inorganic halides include PC13, PBr3, PC15, POC13, POBr3, BF3, Bai3, BBr3, SiF4, SiC4, SiBr4, Sil4, AsCI3, AsBr3, Asti, Se04, SeBr4, TeC14, TeBr4, and Tel4. <BR> <BR> <P>Suitable metallic halides include SnCl4, SnBr4, AIC13, AlBr3, SbCl3,<BR> SbCI5, SbBr3, All3, AIF3, GaCl3, GaBr3, Gal3, GaF3, InCI3, InBr3, Inl3, InF3, TiC4, TiBr4, Ti4, ZnCI2, ZnBr2, Znl2, and ZnF2.

Suitable organometallic halides include di (R") aluminum chloride, bromide, or fluoride where R"is methyl or ethyl ; R"-aluminum dichloride, dibromide, and difluorid where R"is as above; R-aluminum sesquichloride where R'is methyl, ethyl, or isobutyl ; methylmagnesium chloride, bromide, or iodide; ethylmagnesium chloride or bromide; butylmagnesium chloride or bromide; phenylmagnesium chloride or bromide; benzylmagnesium chloride, tri (R") tin chloride or bromide where R"is as above; di-t-butyltin dichloride or dibromide; dibutyltin dichloride or dibromide; and tributyltin chloride or bromide.

Useful silyl phosphonate compounds that can be employed in the catalyst composition include acyclic silyl phosphonates, cyclic silyl phosphonates, and mixtures thereof. Acyclic silyl phosphonates may be represented by the structure:

where each R'independently is H or a mono-valent organic group.

Preferably, each R1 is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups, with each group preferably containing from 1 C atom (or the appropriate minimum number of C atoms to form the group in question) up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. The acyclic silyl phosphonates may be associated in dimeric, trimeric or oligomeric forms by hydrogen bonding.

Suitable acyclic silyl phosphonates include bis (trimethylsilyl) phosphonate, bis (dimethylsilyl) phosphonate, bis (triethylsilyl) phosphonate, bis (diethylsilyl) phosphonate, bis (tri-n-propylsilyl) phosphonate, bis (di-n- propylsilyl) phosphonate, bis (triisopropylsilyl) phosphonate, bis (diisopropyl- silyi) phosphonate, bis (tri-n-butylsilyl) phosphonate, bis (di-n-butylsilyi) phos- phonate, bis (triisobutylsilyl) phosphonate, bis (diisobutylsilyl) phosphonate, bis (tri-t-butylsilyl) phosphonate, bis (di-t-butylsilyi) phosphonate, bis (trihexyl- silyl) phosphonate, bis (dihexylsilyl) phosphonate, bis (trioctylsilyl) phospho- nate, bis (dioctylsilyl) phosphonate, bis (tricyclohexylsilyl) phosphonate, bis (dicyclohexylsilyl) phosphonate, bis (triphenylsilyl) phosphonate, bis (di- phenylsilyl) phosphonate, bis (tri-p-tolylsilyi) phosphonate, bis (di-p-tolylsilyl) phosphonate, bis (tribenzylsilyl) phosphonate, bis (dibenzylsilyl) phosphonate, bis (methyldiethylsilyl) phosphonate, bis (methyldi-n-propylsilyl) phosphonate, bismethyidiisopropylsilyl) phosphonate, bis (methyidi-n-butylsilyl) phospho-

nate, bis (methyidiisobutylsilyl) phosphonate, bis (methyidi-t-butylsilyl) phosphonate, bis (methyldiphenylsilyl) phosphonate, bis (dimethylethylsilyl) phosphonate, bis (dimethyl-n-propylsilyl) phosphonate, bis (dimethyliso- propylsilyl) phosphonate, bis (dimethyl-n-butylsilyl) phosphonate, bis (di- methylisobutylsilyl) phosphonate, bis (dimethyl-t-butylsilyl) phosphonate, bis (dimethylphenylsilyl) phosphonate, bis (t-butyidiphenylsilyl) phosphonate, bis [tris (2-ethylhexyl) silyl] phosphonate, bis [bis (2-ethylhexyl) silyl] phospho- nate, bis [tris (nonylphenyl) silyl] phosphonate, bis [tris (2,4,6-trimethylphenyl)- silyl] phosphonate, bis [bis (2,4,6-trimethylphenyl) silyl] phosphonate, bis [tris- (4-fluorophenyl) silyl] phosphonate, bis [bis (4-fluorophenyl) silyl] phosphonate, bis [tris (pentafluorophenyl) silyl] phosphonate, bis [tris (trifluoromethyl) silyl] phosphonate, bis [tris (2,2,2-trifluoroethyl) silyl] phosphonate, bis [tris (trimethyl- silyl) silyl] phosphonate, bis [tris (trimethylsilylmethyl) silyl] phosphonate, bis [tris (dimethylsilyl) silyl] phosphonate, bis [tris (2-butoxyethyl) silyl] phospho- nate, bis (trimethoxysilyl) phosphonate, bis (triethoxysilyl) phosphonate, bis (triphenoxysilyl) phosphonate, bis [tris (trimethylsilyloxy) silyl] phosphonate, bis [tris (dimethylsilyloxy) silyl] phosphonate, and mixtures thereof.

Cyclic silyl phosphonates contain a ring structure formed by joining the two Si atoms together or by bridging the two Si atoms with one or more divalent organic groups. These cyclic silyl phosphonates may be represented by the structure: where each R independently is H or a monovalent organic group and R3 is a bond between the Si atoms or a divalent organic group. Bicyclic silyl

phosphonates may be formed by joining two R2 groups; therefore, the term cyclic silyl phosphonate includes multi-cyclic silyl phosphonates. Preferably, each R2 is a hydrocarbyl group such as, but not limited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups, with each group preferably containing from 1 C atom (or the appropriate minimum number of C atoms to form the group in question) up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. Preferably, R3 is a hydrocarbylene group such as, but not limited to, alkylen, substituted alkylen, cycloalkylene, substituted cyclo- alkylene, alkenylene, substituted alkenylene, cycloalkenylene, substituted cycloalkenylene, arylen, and substituted arylene groups, with each group preferably containing from 1 C atom (or the appropriate minimum number of C atoms to form the group in question) up to about 20 C atoms. These hydrocarbylene groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. The cyclic silyl phosphonates may be associated in dimeric, trimeric or oligomeric forms by hydrogen bonding.

Suitable cyclic silyl phosphonates include 2-oxo- (2H)-4, 5-disila-1, 3, 2- dioxaphospholane, 2-oxo- (2H)-4, 5-disila-4, 4,5,5-tetramethyl-1,3,2-dioxa- phospholane, 2-oxo- (2H)-4, 5-disila-4, 4,5,5-tetraethyl-1,3,2-dioxaphos- pholane, 2-oxo- (2H)-4, 5-disila-4, 4,5,5-tetraphenyl-1,3,2-dioxaphospholane, 2-oxo- (2H)-4, 5-disila-4, 4,5,5-tetrabenzyl-1,3,2-dioxaphospholane, 2-oxo- (2H)-4,5-disila-4,5-dimethyl-1,3,2-dioxaphospholane, 2-oxo- (2H)-4, 5-disila- 4,5-diethyl-1,3,2-dioxaphospholane, 2-oxo- (2H)-4, 5-disila-4, 5-diphenyl-1,3,2- dioxaphospholane, 2-oxo- (2H)-4, 5-disila-4, 5-dibenzyl-1, 3,2-dioxaphospho- lane, 2-oxo- (2H)-4, 5-disila-4-methyl-1, 3,2-dioxaphospholane, 2-oxo- (2H)- 4,6-disila-1,3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4, 4,6,6-tetra- methyl-1, 3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4, 4,6,6-tetraethyl- 1,3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4, 4,6,6-tetraphenyl-1,3,2- dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4, 4,6,6-tetrabenzyl-1,3,2-dioxa- phosphorinane, 2-oxo- (2H)-4, 6-disila-4, 6-dimethyl-1, 3,2-dioxaphosphori- nane, 2-oxo- (2H)-4, 6-disila-4, 6-diethyl-1, 3,2-dioxaphosphorinane, 2-oxo-

(2H)-4,6-disila-4, 6-diphenyl-1,3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila- 4,6-dibenzyl-1,3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-5, 5-dimethyl- 1,3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-5, 5-diethyl-1, 3,2-dioxaphos- phorinane, 2-oxo- (2H)-4, 6-disila-5, 5-diphenyl-1, 3,2-dioxaphosphorinane, 2- oxo- (2H)-4, 6-disila-5, 5-dibenzyl-1, 3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6- disila-5-ethyl-5-methyl-1, 3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-5- methyl-5-propyl-1, 3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-5-butyl-5- ethyl-1, 3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4-isopropyl-5, 5- dimethyl-1, 3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4-propyl-5-ethyl- 1,3,2-dioxaphosphorinane, 2-oxo- (2H)-4, 6-disila-4-methyl-1, 3,2-dioxaphos- phorinane, and mixtures thereof.

Various organoaluminum compounds or mixtures thereof can be used in the catalyst composition. The term"organoaluminum compound"refers to any Al compound containing at least one covalent Al-C bond. Organoalumi- num compounds that are soluble in a hydrocarbon solvent are preferred.

A preferred class of organoaluminum compounds is represented by the general formula AIRnX3-n where each R independently is a monovalent organic group attached to the Al atom via a C atom; each X independently is a H, a carboxylate group, an alkoxide group, or an aryloxide group; and n is an integer of from 1 to 3. Preferably, each R is a hydrocarbyl group such as, e. g., alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substi- tuted cycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups, with each group preferably containing from 1 C atom (or the appropriate minimum number of C atoms to form the group in question) up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. Preferably, each X is a carboxylate group, an alkoxide group, or an aryloxide group, with each group preferably containing from 1 C atom (or the appropriate minimum number of C atoms to form the group in question) up to about 20 C atoms.

Suitable organoaluminum compounds include, but are not limited to, trihydrocarbylaluminum, dihydrocarbylaluminum hydride, hydrocarbyl- aluminum dihydride, dihydrocarbylaluminum carboxylate, hydrocarbyl-

aluminum bis (carboxylate), dihydrocarbylaluminum alkoxide, hydrocarbyl- aluminum dialkoxide, dihydrocarbylaluminum aryloxide, hydrocarbyl- aluminum diaryloxide, and the like, and mixtures thereof. Trihydrocarbyl- aluminum compounds are generally preferred.

Specific organoaluminum compounds include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-propylaluminum, triisopropyl- aluminum, tri-n-butylaluminum, tri-t-butylaluminum, tri-n-pentylaluminum, trineopentylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tris (2-ethyl- hexyl) aluminum, tricyclohexylaluminum, tris (1-methylcyclopentyl) aluminum, triphenylaluminum, tri-p-tolylaluminum, tris (2,6-dimethylphenyl) aluminum, tribenzylaluminum, diethylphenylaluminum, diethyl-p-tolylaluminum, diethyl- <BR> <BR> benzylaluminum, ethyldiphenylaluminum, ethyldi-p-tolylaluminum, ethyldi- benzylaluminum, diethylaluminum hydride, di-n-propylaluminum hydride, diisopropylaluminum hydride, di-n-butylaluminum hydride, diisobutyl- aluminum hydride, di-n-octylaluminum hydride, diphenylaluminum hydride, di-p-tolylaluminum hydride, dibenzylaluminum hydride, phenylethylaluminum hydride, phenyl-n-propylaluminum hydride, phenylisopropylaluminum hydride, phenyl-n-butylaluminum hydride, phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride, p-tolylethylaluminum hydride, p-tolyl-n- propylaluminum hydride, p-tolylisopropylaluminum hydride, p-tolyl-n-butyl- aluminum hydride, p-tolylisobutylaluminum hydride, p-tolyl-n-octylaluminum hydride, benzylethylaluminum hydride, benzyl-n-propylaluminum hydride, benzylisopropylaluminum hydride, benzyl-n-butylaluminum hydride, benzyl- isobutylaluminum hydride, and benzyl-n-octylaluminum hydride, ethylalum- inum dihydride, n-propylaluminum dihydride, isopropylaluminum dihydride, n-butylaluminum dihydride, isobutylaluminum dihydride, n-octylaluminum dihydride, dimethylaluminum hexanoate, diethylaluminum octoate, diiso- butylaluminum 2-ethylhexanoate, dimethylaluminum neodecanoate, diethyl- aluminum stearate, diisobutylaluminum oleate, methylaluminum bis (hexa- noate), ethylaluminum bis (octoate), isobutylaluminum bis (2-ethylhexanoate), methylaluminum bis (neodecanoate), ethylaluminum bis (stearate), isobutyl- aluminum bis (oleate), dimethylaluminum methoxide, diethylaluminum meth-

oxide, diisobutylaluminum methoxide, dimethylaluminum ethoxide, diethyl- aluminum ethoxide, diisobutylaluminum ethoxide, dimethylaluminum phen- oxide, diethylaluminum phenoxide, diisobutylaluminum phenoxide, methyl- aluminum dimethoxide, ethylaluminum dimethoxide, isobutylaluminum dimethoxide, methylaluminum diethoxide, ethylaluminum diethoxide, iso- butylaluminum diethoxide, methylaluminum diphenoxide, ethylaluminum diphenoxide, isobutylaluminum diphenoxide, etc., and mixtures thereof.

Another class of organoaluminum compounds is aluminoxanes which include oligomeric linear aluminoxanes represented by the formula : and oligomeric cyclic aluminoxanes represented by the formula : where x is an integer of from 1 to about 100, preferably from about 10 to about 50; y is an integer of from 2 to about 100, preferably from about 3 to about 20; each R4 independently is a monovalent organic group attached to the Al atom via a C atom. Preferably, each R4 is a hydrocarbyl group such as, e. g., alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substi- tuted cycloalkenyl, aryl, substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups, with each group preferably containing from 1 C atom (or the appropriate minimum number of C atoms to form the group in question) up to about 20 C atoms. These hydrocarbyl groups may contain heteroatoms such as, but not limited to, N, O, Si, S, and P. (The number of moles of the aluminoxane as used in this application refers to the number of moles of the

Al atoms rather than the number of moles of the oligomeric aluminoxane molecules. This convention is commonly employed in the art of catalysis utilizing aluminoxanes.) Aluminoxanes can be prepared by reacting trihydrocarbylaluminum compounds with water. This reaction can be performed according to known methods such as (1) a method in which the trihydrocarbylaluminum compound is dissolved in an organic solvent and then contacted with water, (2) a method in which the trihydrocarbylaluminum compound is reacted with water of crystallization contained in, for example, metal salts, or water adsorbed in inorganic or organic compounds, and (3) a method in which the trihydrocarbylaluminum compound is reacted with water in the presence of the monomer or monomer solution to be polymerized.

Suitable aluminoxane compounds include methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, n-propylalumin- oxane, isopropylaluminoxane, butylaluminoxane, isobutylaluminoxane, n- pentylaluminoxane, neopentylaluminoxane, n-hexylaluminoxane, n-octyl- <BR> <BR> aluminoxane,2-ethylhexylaluminoxane, cylcohexylaluminoxane, 1-methyl- cyclopentylaluminoxane, phenylaluminoxane, 2,6-dimethylphenylalumin- oxane, and the like, and mixtures thereof. Isobutylaluminoxane is particu- larly useful on the grounds of its availability and its solubility in aliphatic and cycloaliphatic hydrocarbon solvents. MMAO can be formed by substituting about 20-80% of the methyl groups of MAO with C2-C12 hydrocarbyl groups, preferably with isobutyl groups, using techniques known in the art.

The present catalyst composition has very high catalytic activity for oligomerizing conjugated dienes over a wide range of total catalyst concen- trations and catalyst ingredient ratios. The oligomerization products having the most desirable properties, however, are obtained within a narrower range of total catalyst concentrations and ingredient ratios. Further, the catalyst ingredients are believed to interact to form an active catalyst species. Accordingly, the optimum concentration for any one catalyst ingredient depends on the concentrations of the other catalyst ingredients.

In the embodiment where the catalyst composition includes (a) a halogen-containing Fe compound, the molar ratio of the silyl phosphonate to the halogen-containing Fe compound (P/Fe) can be varied from about 0.5: 1 to about 50: 1, more preferably from about 1: 1 to about 25: 1, and even more preferably from about 2: 1 to about 10: 1. The molar ratio of the organo- aluminum compound to the Fe-containing compound (Al/Fe) can be varied from about 1: 1 to about 200: 1, more preferably from about 2: 1 to about 100: 1, and even more preferably from about 3: 1 to about 50: 1.

In the embodiment where the catalyst composition includes an Fe- containing compound and a halogen-containing compound, the molar ratio of the silyl phosphonate to the Fe-containing compound (P/Fe) can be varied from about 0.5: 1 to about 50: 1, more preferably from about 1: 1 to about 25: 1, and even more preferably from about 2: 1 to about 10: 1. The molar ratio of the halogen-containing compound to the Fe-containing compound (halogen/Fe) can be varied from about 0.5: 1 to about 20: 1, more preferably from about 1: 1 to about 10: 1, and even more preferably from about 2: 1 to about 6: 1. The molar ratio of the organoaluminum compound to the Fe- containing compound (Al/Fe) can be varied from about 1: 1 to about 200: 1, more preferably from about 2: 1 to about 100: 1, and even more preferably from about 3: 1 to about 50: 1.

The catalyst composition is formed by combining or mixing the catalyst ingredients. Although an active catalyst species is believed to result from this combination, the degree of interaction or reaction between the various ingredients is not known with any certainty. Therefore, the term "catalyst composition"encompasses a simple mixture of the ingredients, a complex of the various ingredients caused by physical or chemical forces of attraction, a chemical reaction product of the ingredients, or a combination of the foregoing.

The catalyst composition may be formed in situ by adding the ingredients to a solution containing monomer and solvent, or simply bulk monomer, in either a stepwise or simultaneous manner. When adding the ingredients in a stepwise manner, the order in which they are added is not

critical. In the first embodiment, adding the halogen-containing Fe compound followed by the silyl phosphonate and then the organoaluminum (org-AI) compound is preferred. In the second embodiment, adding the Fe- containing compound first followed by the silyl phosphonate, then the halogen-containing compound, and finally the org-AI compound is preferred.

Second, the catalyst ingredients may be pre-mixed outside the oligomerization system at an appropriate temperature, generally from about - 20° to about 80°C, and the resulting catalyst composition then is added to the monomer solution.

Third, the catalyst composition may be pre-formed in the presence of monomer, i. e., the catalyst ingredients are pre-mixed in the presence of a small amount of the conjugated diene monomer at an appropriate tempera- ture, generally from about-20° to about 80°C. The amount of conjugated diene monomer used for pre-forming the catalyst, per mole of the Fe- containing compound or halogen-containing Fe compound, can range from about 1 to about 500 moles, more preferably from about 5 to about 250 moles, and even more preferably from about 10 to about 100 moles. The resulting catalyst composition is added to the remainder of the monomer to be oligomerized.

Fourth, the catalyst composition can be formed by using a two-stage procedure. The first stage involves reacting the Fe-containing compound or halogen-containing Fe compound with the org-AI compound in the presence of a small amount of conjugated diene monomer at an appropriate temper- ature, generally from about-20° to about 80°C. In the second stage, the foregoing reaction mixture, the silyl phosphonate, and where appropriate the halogen-containing compound are charged in either a stepwise or simulta- neous manner to the remainder of monomer to be oligomerized.

Fifth, and most preferably, an Fe-ligand complex is first formed by pre-combining the iron-containing compound or the halogen-containing Fe compound with the silyl phosphonate. Once formed, this Fe-ligand complex is combined with the org-AI compound, and where appropriate the halogen- containing compound, to form the active catalyst species. The Fe-ligand

complex can be formed separately or in the presence of conjugated diene monomer to be oligomerized. This complexation reaction can be conducted at any convenient temperature and normal pressure but, for an increased rate of reaction, this reaction preferably is performed at room temperature or above. The time required for the formation of the Fe-ligand complex is usually within the range of about 10 to about 120 minutes after mixing the Fe-containing or halogen-containing iron compound with the silyl phospho- nate. The temperature and time used for the formation of the Fe-ligand complex depends on several variables including the particular starting materials and solvent employed. Once formed, the Fe-ligand complex can be used without isolation from the complexation mixture. If desired, however, the Fe-ligand complex may be isolated from the complexation mixture before use.

When a solution of the catalyst composition or one or more of the catalyst ingredients is prepared outside the oligomerization system as set forth in the foregoing methods, an organic solvent or carrier preferably is employed. The organic solvent may serve to dissolve the catalyst compo- sition or ingredients, or the solvent may simply serve as a carrier in which the catalyst composition or ingredients may be suspended. Desirably, an organic solvent that is inert with respect to the catalyst composition is used. Useful solvents include hydrocarbon solvents such as aromatic hydrocarbons, ali- phatic hydrocarbons, and cycloaliphatic hydrocarbons. Non-limiting examples of aromatic hydrocarbon solvents include benzene, toluene, xylenes, ethyl- benzene, diethylbenzene, mesitylene, and the like. Non-limiting examples of aliphatic hydrocarbon solvents include n-pentane, n-hexane, n-heptane, n- octane, n-nonane, n-decane, isopentane, isohexanes, isopentanes, isooc- tanes, 2,2-dimethylbutane, petroleum ether, kerosene, petroleum spirits, and the like. Non-limiting examples of cycloatiphatic hydrocarbon solvents include cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, and the like. Commercial mixtures of the above hydrocarbons may also be used. For environmental reasons, aliphatic and cycloaliphatic solvents are preferred.

The catalyst composition of this invention exhibits very high activity for the oligomerization of conjugated dienes. Some specific examples of suitable conjugated dienes that can be oligomerized by means of the catalyst composition include 1,3-butadiene, isoprene, 1,3-pentadiene, 1,3- hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1, 3-butadiene, 2-methyl-1, 3- pentadiene, 3-methyl-1, 3-pentadiene, 4-methyl-1, 3-pentadiene, and 2,4- hexadiene. The preferred monomers are 1,3-butadiene, isoprene, 1,3- pentadiene, and 1,3-hexadiene. Mixtures of two or more conjugated dienes may also be utilized in co-oligomerization.

The production of conjugated diene oligomers is accomplished by oligomerizing conjugated diene monomers in the presence of a catalytically effective amount of the foregoing catalyst composition. The total catalyst concentration to be employed in the oligomerization mass depends on the interplay of various factors such as the purity of the ingredients, the oligo- merization rate and conversion desired, the oligomerization temperature, and many other factors. Accordingly, specific total catalyst concentrations cannot be definitively set forth except to say that catalytically effective amounts of the respective catalyst ingredients should be used. Generally, the amount of the Fe-containing compound or halogen-containing Fe compound used, per 100 g of conjugated diene monomer, can be varied from about 0.01 to about 2 mmol, with a more preferred range being from about 0.02 to about 1.0 mmol per 100 g, and a most preferred range being from about 0.05 to about 0.5 mmol.

Oligomerization is preferably carried out in an organic solvent as diluent. That is, an amount of organic solvent in addition to the organic solvent that may be used in preparing the catalyst composition is added to the oligomerization system. The additional organic solvent may be either the same as or different from the organic solvent contained in the catalyst solutions. Preferably, an organic solvent that is inert with respect to the catalyst composition employed to catalyze the oligomerization reaction is selected. Exemplary hydrocarbon solvents have been set forth above.

The concentration of conjugated diene monomer to be oligomerized is not limited to a special range. Preferably, however, the concentration in the oligomerization medium at the beginning of the oligomerization is in a range of from about 3 to about 80% by weight, more preferably from about 5 to about 50% by weight, and even more preferably from about 10 to about 30% by weight.

Oligomerization may also be carried out by means of bulk oligomerization, i. e., a reaction environment where no solvents are employed. Bulk oligomerization can be conducted either in a condensed liquid phase or a gas phase.

Oligomerization may be carried out as a batch process, continuous process, or even semi-continuous process. In the semi-continuous process, conjugated diene monomer is intermittently charged as needed to replace that monomer already oligomerized. In any case, the oligomerization is desirably conducted under anaerobic conditions by using an inert protective gas such as N2, Ar or He, with moderate to vigorous agitation. The oligo- merization temperature employed may vary widely from a low temperature such as-1 0°C or below to a high temperature such as 100°C or above, with a preferred temperature range being from about 20° to about 90°C. In general, elevated temperatures are undesirable due to thermal polymer- zation of the oligomers. The heat of oligomerization may be removed by external cooling, cooling by evaporation of conjugated diene monomer or solvent, or a combination of the two methods. Although the pressure employed in the practice of this invention also may vary widely, a preferred pressure range is from about 100 to about 1000 kPa.

The reaction time for the oligomerization process can vary widely but generally is from a few minutes, e. g., 5 minutes, to a few hours, e. g., 8 hours, depending on such factors as the type of conjugated diene, the temperature, the catalyst concentration, the catalyst ingredient ratio, and the conversion desired. In general, due to the very high catalytic activity of the catalyst composition, the reaction time is quite short even with the use of very low catalyst levels. Therefore, high conversion and high productivity in

terms of unit mass of product per unit mass of catalyst per hour are realized.

Furthermore, since the catalyst composition of this invention is highly active even at low temperatures, the oligomerization of conjugated dienes may be carried out under very mild temperature conditions, thereby minimizing the formation of undesirable by-products.

Once a desired conversion is achieved, the oligomerization reaction can be stopped by adding a terminator to inactivate the catalyst. Typically, the terminator employed is a protic compound such as, but not limited to, an alcohol, a carboxylic acid, an inorganic acid, water, or a combination thereof.

A stabilizer such as 2,6-di-tert-butyl-4-methylphenol may be added along with, before, or after addition of the terminator. The amount of stabilizer employed is usually in the range of 0.01 to 0.1% by weight of the oligomer- zation product. When the oligomerization has been stopped, the products can be recovered from the mixture by conventional techniques, such as fractional distillation and preparative chromatography, known in the art.

To demonstrate the practice the present invention, the following examples have been prepared and tested as described. The examples should not, however, be viewed as limiting the scope of the invention.

EXAMPLES Example 1 Bis (trimethylsilyl) phosphonate was synthesized by reacting H3PO3 with hexamethyldisiloxane in the presence of anhydrous ZnCl2 as the catalyst. Anhydrous H3PO3 (33.1 g, 0.404 mol), hexamethyldisiloxane (98.4 g, 0. 606 mol), anhydrous ZnCI2 (2.0 g, 0.015 mol), and benzene (240 mL) were mixed in a round-bottom reaction flask which was connected to a Dean-Stark trap and a reflux condenser. The mixture was heated to reflux for 24 hours, with continuous removal of water via the trap.

The reaction flask was then connected to a distillation head and a receiving flask. The benzene solvent and unreacted hexamethyldisiloxane were removed by distillation at atmospheric pressure. The remaining crude

product was distilled under vacuum, yielding bis (trimethylsilyl) phosphonate as a colorless liquid (51.7 g, 0.228 mol, 57% yield).

The identity of the product was established by NMR spectroscopy. 1H NMR data (CDCb, 25°C, referenced to TMS). 6. 85 (doublet, R 1JHp = 699 Hz, 1 H, H-P), 0.31 (singlet, 18 H, CH3). 13p NMR data (CDCIs, 25°C, referenced to external 85% H3PO4)-14. 2 (doublet, 1JHP = 698 Hz).

Example 2 Inside a glovebox operated under an Ar atmosphere, an oven-dried glass bottle was charged with 228 mg (1.80 mmol) anhydrous FeCl2 powder and 1.63 g (7.20 mmol) bis (trimethylsilyl) phosphonate. The bottle was capped with a self-sealing rubber liner and a perforated metal cap prior to being removed from the glovebox and being charged with toluene (27.6 mL).

The bottle was shaken at room temperature for 2 hours, resulting in the dissolution of the FeCl2 solid and the formation of a pale-yellow solution containing the complex of FeCl2 with bis (trimethylsilyl) phosphonate ligand.

The concentration of the Fe-ligand complex in the solution was calculated to be 0.0614 mmol/mL.

Example 3 Inside a glovebox operated under an Ar atmosphere, an oven-dried glass bottle was charged with 292 mg (1.80 mmol) anhydrous FeCls powder and 1.63 g (7.20 mmol) bis (trimethylsilyl) phosphonate. The bottle was capped with a self-sealing rubber liner and a perforated metal cap prior to being removed from the glovebox and being charged with toluene (30.4 mL).

The bottle was shaken at room temperature for 5 minutes, resulting in the dissolution of the FeCl3 solid and the formation of a yellow solution containing the complex of FeCls with bis (trimethylsilyl) phosphonate ligand.

The concentration of the Fe-ligand complex in the solution was calculated to be 0.0559 mmol/mL.

Example 4 Inside a glovebox operated under an Ar atmosphere, an oven-dried glass bottle was charged with 388 mg (1.80 mmol) anhydrous FeBr2 powder and 1.63 g (7.20 mmol) bis (trimethylsilyl) phosphonate. The bottle was capped with a self-sealing rubber liner and a perforated metal cap prior to being removed from the glovebox and being charged with toluene (27.5 mL).

The bottle was tumbled for 10 hours in a water bath maintained at 80°C, resulting in the dissolution of the FeBr2 solid and the formation of an orange solution containing the complex of FeBr2 with bis (trimethylsilyl) phosphonate ligand. The concentration of the Fe-ligand complex in the solution was calculated to be 0.0615 mmol/mL.

Example 5 Inside a glovebox operated under an Ar atmosphere, an oven-dried glass bottle was charged with 532 mg (1.80 mmol) anhydrous FeBr3 powder and 1.63 g (7.20 mmol) bis (trimethylsilyl) phosphonate. The bottle was capped with a self-sealing rubber liner and a perforated metal cap prior to being removed from the glovebox and being charged with toluene (29.6 mL).

The bottle was shaken at room temperature for 10 minutes, resulting in the dissolution of the FeBr3 solid and the formation of a deep-red solution containing the complex of FeBr3 with bis (trimethylsilyl) phosphonate ligand.

The concentration of the Fe-ligand complex in the solution was calculated to be 0.0575 mmol/mL.

Examples 6-9 An oven-dried 1 L glass bottle was capped with a self-sealing rubber liner and a perforated metal cap. After the bottle was thoroughly purged with a stream of dry N2, the bottle was charged with 230.4 g of a 1,3-butadiene/ hexanes blend containing 21.7% 1,3-butadiene, followed by w mmol triiso- butylaluminum (where w varied from one experiment to the next) and 0.050 mmol of the complex prepared in Example 2. The bottle was placed in a water bath maintained at room temperature. After 6 hours, the oligomer- zation was terminated by adding 0.30 mL isopropanol.

Analysis of the resulting oligomerization mixture by GC/MS indicated that x% of the 1,3-butadiene monomer had been converted, the product being a mixture of y% 5-methyl-1, 3,6-heptatriene and z% 1,3,6-octatriene.

The experimental data are summarized immediately below in Table I.

Table I 6789 w (mmol) 0.45 0.50 0.55 0. 60 Fe/AI molar ratio 1 : 9 1 : 10 1: 11 1: 12 x (%) after 6 hours 99. 9 99.8 100 100 Oligomerization product composition: y (%) 90.5 90.4 90.4 90.6 z (%) 9.5 9.6 9.6 9.4 Examples 10-13 The procedure of Example 6 was repeated except that the complex of Example 3 was used. The monomer charge, the amounts of the catalyst ingredients, and the oligomerization product composition are summarized in Table 11.

Table II 10 11 12 13 w (mmol) 0.45 0.50 0.55 0.60 Fe/AI molar ratio 1 : 9 1 : 10 1: 11 1: 12 x (%) after 6 hours 100 100 99.9 100 Oligomerization product composition: y (%) 90. 3 90.4 90.4 90.4 z (%) 9.7 9.5 9.6 9.6 Examples 14-17 The procedure in Example 6 was repeated except that the complex of Example 4 was used. The monomer charge, the amounts of the catalyst ingredients, and the oligomerization product composition are summarized in Table Ill.

Table III 14 15 16 17 i-Bu3AI (mmol) 0.45 0.50 0.55 0.60 Fe/AI molar ratio 1 : 9 1 : 10 1 : 11 1 : 12 w (%) after 6 hours 99. 4 99.5 99.6 99.6 Oligomerization product composition: y (%) 92.1 91.8 92.1 92.1 z (%) 7.9 8.2 7.9 7. 9 Examples 18-21 The procedure in Example 6 was repeated except that the complex of Example 5 was used. The monomer charge, the amounts of the catalyst ingredients, and the oligomerization product composition are summarized in Table IV.

Table IV 18 19 20 21 w (mmol) 0.45 0.50 0.55 0.60 Fe/AImolarratio 1 : 9 1 : 10 1 : 11 1 : 12 x (%) after 6 hours 99. 1 99. 3 99. 4 99.4 Oligomerization product composition: y (%) 92.4 92.2 92.1 92.0 z (%) 7. 6 7.8 7.9 8. 0 The results described in Examples 6-21 show that, at mild temperature conditions, 1,3-butadiene can be converted substantially quantitatively to the two acyclic dimers with a selectivity of 100% by utilizing the catalyst composition of the present invention.

Examples 22-26 An oven-dried 1 L glass bottle was capped with a self-sealing rubber liner and a perforated metal cap. After the bottle was thoroughly purged with a stream of dry N2, the bottle was charged with 230.4 g of a 1,3-butadiene/

hexanes blend containing 21.7% by weight of 1,3-butadiene. The following catalyst ingredients were then charged in the following order and amounts: 0.050 mmol iron (III) 2-ethylhexanoate, 0.20 mmol bis (trimethylsilyl) phosphonate, 0.15 mmol diisobutylaluminum chloride, and a mmol triisobutylaluminum (where a varied by sample).

The bottle was placed in a water bath maintained at room temperature.

After 7 hours, the oligomerization was terminated by adding 0.30 mL isopropanol.

Analysis of the resulting oligomerization mixture by GC/MS indicated that b% of the 1,3-butadiene monomer had been converted, the product being a mixture of c% 5-methyl-1, 3,6-heptatriene and d% 1,3,6-octatriene.

The experimental data are summarized in Table V.

Table V 22 23 24 25 26 a (mmol) 0.25 0.30 0.35 0.40 0.45 Fe/P/CI/AI molar ratio 1 : 4: 3: 5 1: 4: 3: 6 1: 4: 3: 7 1: 4: 3: 8 1: 4: 3: 9 b (%) after 7 hours 98. 9 99.6 99.9 99.9 99.9 Oligomerization product composition: c (%) 90.9 90.1 89.9 89.9 89.7 d (%) 9.1 9.9 10.1 10.1 10.3 The results described in Examples 22-26 show that at mild temperature conditions, 1,3-butadiene can be converted substantially quantitatively to the two acyclic dimers with a selectivity of 100% by utilizing the catalyst composition of the present invention.