Description

The present invention relates to a process for preparing diimine compounds.

The use of metallocene catalysts in the polymerization of unsaturated compounds has had a great influence on the preparation of polyolefins, since it opens up a route to new types of polyolefinic materials or to materials having improved properties. There is therefore great interest in the development of new families of catalysts for the polymerization of unsaturated compounds in or¬ der to obtain even better control over the properties of polyolefins or to obtain further novel prod¬ ucts.

In particular, the use of transition metal catalysts comprising late transition metals is of interest because they are able to tolerate heteroatom functions. Transition metal catalysts comprising late transition metals which are suitable for the polymerization of unsaturated compounds are known from the prior art. Here, 1 ,2-diiminenickel and 2,6-bis(imino)pyridyliron complexes have been found to be particularly useful.

The ligand systems such as 1 ,2-diimine or 2,6-bis(imino)pyridyl compounds are usually prepared via condensation of the corresponding diketo compounds with primary amines. Since in this reac¬ tion two keto functions have to be converted into the corresponding imines, the yields of diimine compound are often low. Particularly when primary amines having electron-withdrawing or bulky groups are used, the yield of diimine product drops. It is often the case here that only one of the two keto functions is converted into the imine. Furthermore, the reaction time usually has to be increased significantly in order to obtain at least a small yield of the diimine.

WO 98/27124 discloses the synthesis of 2,6-bis(imino)pyridyl compounds from the corresponding diketo compounds and anilines in methanol with addition of catalytic amounts of formic acid. When anilines bearing a halogen in the 2 position are used, the yield is only very low.

WO 01/07491 describes the synthesis of 2,6-bis(imino)pyridyl compounds from the corresponding keto compounds and ortho-halogen-substituted anilines in benzene in the presence of catalytic amounts of p-toluenesulfonic acid using a water separator. Here too, the yield of 2,6- bis(imino)pyridyl compound is below 50%.

In Synlett. 2003, (10), pp.1419-1422, C. Qian et al. compares a number of synthetic routes for preparing halogen-substituted 2,6-bis(imino)pyridyl compounds. The best results are achieved by means of a combination of Al-Si-catalyst and 4 A molecular sieves. It is an object of the present invention to provide an improved process for synthesizing diimine compounds, by means of which even primary amines having electron-withdrawing or bulky sub- stituents can be converted into the corresponding diimine compounds in high yields.

We have accordingly found a process for preparing diimine compounds wherein a dicarbonyl compound is reacted with primary amines in the presence of phosphorus pentoxide.

In the process of the invention, a diimine compound is any compound which contains at least two imine groups -C=N- which is not part of a heteroaromatic ring.

Preference is given to diimine compounds of the formula I

where the variables have the following meanings: R1-R4 are each, independently of one another, hydrogen, CrC^-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, NR52, or a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S, where the organic radicals R1-R4 may also be substituted by halogens, NR52, OR5 or SiR63 and/or two radicals R1- R4 may also be joined with one another or with A to form a ring,

the radicals R5 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR63, where the organic radicals R5 may also be substituted by halogens and two radicals R5 may also be joined to form a five- or six-membered ring, and

the radicals R6 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part and two radicals R6 may also be joined to form a five- or six-membered ring,

m is 0 or 1 ,

or a heteroaromatic ring system, where

L1-L2 are each, independently of one another, silicon or germanium,

R7-R15 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-all<enyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR163, where the organic radicals R7-R15 may also be substi¬ tuted by halogens and two radicals R7-R15 may also be joined to form a five- or six- membered.ring, and

the radicals R16 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part and two radicals R16 may also be joined to form a five- or six-membered ring.

In the process of the invention, a dicarbonyl compound is any compound which contains at least two keto groups, -C=O, which are not part of a heteroaromatic ring, with aldehyde groups also being included.

Preference is given to dicarbonyl compounds of the formula Il

where the variables have the following meanings: R1-R2 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, NR52, or a five-, six- or seven-mem bered heterocycle containing at least one atom from the group consisting of N, P, O and S, where the organic radicals R1-R4 may also be substituted by halogens, NR52, OR5 or SiR63 and/or two radicals R1- R2 may also be joined with one another or with A to form a ring,

the radicals R5 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR63, where the organic radicals R5 may also be substituted by halogens and two radicals R5 may also be joined to form a five- or six-membered ring, and

the radicals R6 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, •C6-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 c caarrbboonn a attoommss i inn t thhee aryl part and two radicals R6 may also be joined to form a five- or six-membered ring,

m is 0 or 1 ,

or a heteroaromatic ring system, where

L 1 - iL 2 are each, independently of one another, silicon or germanium,

R7-R15 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyI, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR163, where the organic radicals R7-R15 may also be substi¬ tuted by halogens and two radicals R7-R15 may also be joined to form a five- or six- membered ring, and

the radicals R16are each, independently of one another, hydrogen, C1-C^-SIkVl1 C2-C22-alkenyl, C6-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part and two radicals R16 may also be joined to form a five- or six-membered ring.

In the process of the invention, a primary amine is any compound which bears an NH2 group, i.e. including hydrazines.

The process of the invention is preferably employed for preparing diimine compounds of the formula I by reacting the dicarbonyl compound of the formula Il with primary amines in the pres¬ ence of phosphorus pentoxide. Primary amines used here are NH2R3, and NH2R4, where the meanings of R3 and R4 and their preferred embodiments correspond to those given for the diimine compound of the formula I. Preference is given to NH2R3 and NH2R4 being identical, so that R3 and R4 in the diimine compound I are also identical. Examples of primary amines are methyl- amine, ethylamine, n-propylamine, isopropylamine, n-butylamine, tert-butylamine, sec-butylamine, isobutylamine, tert-amylamine, n-pentylamine, n-hexylamine, n-octylamine, cyclohexylamine, aniline, 2-methyIaniline, 2-chloroaniIine, 2-bromoaniline, 2,6-dichloroaniline, 2,4-dichloro-6- methylaniline and 2,6-dibromoaniline. R3 and R4 preferably contain a halogen-containing substitu- ent.

The substituents R1-R2 of the diimine compound of the formula I and of the dicarbonyl compound of the formula I! and R3-R4 of the diimine compound of the formula I can be varied within wide ranges. Possible carboorganic substituents R1-R4 are, for example, the following: CrC22-alkyl which may be linear or branched, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert- butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl or n-dodecyl, 5- to 7-membered cyclo- alkyl which may in turn bear a CrC10-alkyl group and/or C6-C10-aryl group as substituent, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclodode- cyl, C2-C22-alkenyl which may be linear, cyclic or branched and in which the double bond may be internal or terminal, e.g. vinyl, 1-allyl, 2-allyl, 3-allyl, butenyl, pentenyl, hexenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl or cyclooctadienyl, C6-C22-aryl which may be substituted by further alkyl groups, e.g. phenyl, naphthyl, biphenyl, anthranyl, o, m-, p-methylphenyl, 2,3-, 2,4-, 2,5- or 2,6-dimethylphenyl, 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6- or 3,4,5-trimethylphenyl, or arylalkyl, which may bear further alkyl groups as substituents, e.g. benzyl, o-, m-, p-methylbenzyl, 1- or 2- ethylphenyl, where, if appropriate, two radicals R1-R2 may also be joined to one another or to A to form a 5-, 6-, 7- or 8-membered ring which may also be a heterocycle containing at least one atom from the group consisting of N, P, O and S. Furthermore, R1 -R4 can be amino NR52, for - example dimethylamino, N-pyrroiidinyl, diphenylamino or picolinyl. In this amino group, it is pre¬ ferred that none of the substituents R5 is hydrogen. The organic radicals R1-R4 may also be substituted by halogens such as fluorine, chlorine or bromine, by amino NR52, for example dimethylamino, N-pyrrolidinyl or picolinyl, by alkoxy or aryloxy OR5, e.g. methoxy, ethoxy or isopropoxy, or organosilicon substituents SiR63, e.g. trimethylsilyl, triethylsilyl, butyldimethylsilyl, tributylsilyl, tri-tert-butylsilyl, triailylsilyl, triphenylsilyl or dimethylphenylsiiyl. Possible substituents R5 are the same carboorganic radicals as described in more detail above for R1-R4, where, if ap¬ propriate, two R5 radicals may be joined to form a 5- or 6-membered ring and/or be substituted by halogen. A possible radical R6 in organosilicon substituents SiR63 are the same carboorganic radicals as described in more detail above for R1-R4, where, if appropriate, two R6 radicals may also be joined to form a 5- or 6-membered ring. Preference is given to R3 and R4 being identical.

A is a bridge between the two keto or imino groups, preferably comprising carbon- and/or silicon- and/or n-containing bridge members. The activity of the catalyst can be influenced by a change in the length of the linkage between the imino groups.

Possible carboorganic substituents R7-R15 in the linkage A are, for example, the following: hydro¬ gen, CVC22-aIkyl which may be linear or branched, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl or n-dodecyl, 5- to 7- membered cycloalkyl which may in turn bear a C6-C10-aryl group as substituent, e.g. cyclopropyi, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclododecyl, C2-C22-alkenyl which may be linear, cyclic or branched and in which the double bond may be in¬ ternal or terminal, e.g. vinyl, 1-allyl, 2-allyl, 3-allyl, butenyl, pentenyl, hexenyl, cyclopentenyl, cy- clohexenyl, cyclooctenyl or cyclooctadienyi, C6-C2o-aryl which may be further alkyl groups substituted by, e.g. phenyl, naphthyl, biphenyl, anthranyl, o-, m-, p-methylphenyl, 2,3-, 2,4-, 2,5- or 2,6-dimethylphen-1-yl, 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6- or 3,4,5-trimethylphen-1-yl, or arylal¬ kyl, which may bear further alkyl groups as substituents, e.g. benzyl, o-, m-, p-methylbenzyl, 1- or 2-ethylphenyl, where, if appropriate, two radicals R7 to R15 may also be joined to form a 5- or 6- membered ring, cyclohexane, and the organic radicals R7-R15 may also be substituted- by halogens such as fluorine, chlorine or bromine, for example pentafluorophenyl or bis-3,5-trifluoro- methylphen-1-yl. Preferred radicals R7-R15 are hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, benzyl, phenyl, ortho dialkyl- or^ dichloro-substituted phenyls, trialkyl- or trichloro-substituted phenyls, naphthyl, biphenyl and anthranyl. Possible radicals R16 in organosilicon substituents SiR163 are the same radicals as described in more detail above for R7-R15, where, if appropriate, two R16 may also be joined to form a 5- or 6- membered ring, e.g. trimethylsilyl, triethylsilyl, butyldimethylsilyl, tributylsilyl, tri-tert-butylsilyl, trial- lylsilyl, triphenylsilyl or dimethylphenylsilyl.

A can also be a heteroaromatic ring system containing at least one atom from the group consist¬ ing of nitrogen, phosphorus, oxygen and sulfur, particularly preferably nitrogen and sulfur. Prefer¬ ence is given to heteroaromatics having a ring size of 5 or 6 ring atoms. Examples of 5-membered heterocycles which may contain from one to three nitrogen atoms and/or a sulfur or oxygen atom in addition to carbon atoms are 1 ,2-dihydrofuran, furan, thiophene, pyrrole, isoxazole, 3- isothiazole, pyrazole, oxazole, thiazole, imidazole, 1 ,2,4-oxadiazole, 1 ,2,5-oxadiazole, 1 ,3,4- oxadiazole, 1 ,2,3-triazoIe or 1 ,2,4-triazole. Examples of 6-membered heteroaryl groups which may contain from one to four nitrogen atoms and/or a phosphorus atom are pyridine, phospha- benzene, pyridazine, pyrimidine, pyrazine, 1 ,3,5-triazine, 1 ,2,4-triazine and 1 ,2,3-triazine. The 5-membered and 6-membered heterocycles can also be substituted by C1-C1o-alkyl, C6-C10-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-10 carbon atoms in the aryl part, trialkylsilyl or halogens such as fluorine, chlorine or bromine, dialkylamide, alkylarylamide, diarylamide, alkoxy or aryloxy or be fused with one or more aromatics or heteroaromatics. Examples of benzo-fused 5-membered heteroaryl groups are indole, indazole, benzofuran, benzothiophene, benzothiazole, benzoxazole and benzimidazole. Examples of benzo-fused 6-membered heteroaryl groups are chromane, benzopyran, quinoline, isoquinoline, cinnoline, phthalazine, quinazoline, quinoxaline,1 ,10-phenanthroline and quinolizine. Nomenclature and numbering of the heterocycles has been taken from Lettau, Chemie der Heterocyclen, 1st edition, VEB, Weinheim 1979. The two keto or imino groups are preferably located on the heteroaromatic ring system in the ortho positions relative to the same heteroatom, preferably a nitrogen atom.

A is preferably a -CR7R8- group, substituted or unsubstituted 1 ,2-phenylene or - CR7R8CR9R10NR15CR11R12CR13R14- . The above-described preferred embodiments of the sub- stituents R7 to R15 are likewise preferred embodiments here. Preference is given to -CR7R8- being a -CHR8-, -CH2- or -C(CHs)2- group.

In a further, preferred embodiment, A has the formula III

where the variables have the following meanings: E1 is nitrogen or phosphorus, in particular nitrogen,

E2-E4 are each, independently of one another, carbon, nitrogen or phosphorus, in particular carbon,

R17-R 19 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyI, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, halogen, NR 2, OR , SiR 3, where the organic radicals R ,17- rR-,19 may also be substituted by halogens and/or two vicinal radicals R17-R19 may also be joined to form a five-, six- or seven-membered ring, and/or two radicals R17-R19 are joined to form a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S,

the radicals R20 are each, independently of one another, hydrogen, CVC^-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR213, where the organic radicals R20 may also be substituted by halogens and two radicals R20 may also be joined to form a five- or six-membered ring, and

the radicals R21 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22-aryI or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part and two radicals R21 may also be joined to form a five- or six-membered ring,

u is 0 when .E2-E4 is nitrogen or phosphorus and is 1 when E2-E4 is carbon.

The process of the invention has been found to be particularly useful for diimines of the formula I in which m is 0, known as 1 ,2-diimine systems, and those in which m is 1 and A has the formula III. The dicarbonyl compounds of the formula Il from which these are prepared have the same preferred embodiments of the variables m and A. The process of the invention is especially useful for preparing diimines of the formula IV

IV by reacting a dicarbonyl compound of the formula V

with primary amines in the presence of phosphorus pentoxide, where the variables have the following meanings:

are each, independently of one another, carbon or nitrogen, in particular carbon,

R1-R2 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22- aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, where the organic radicals R1-R2 may also be substituted by halogens, NR52, OR5 or SiR63 and/or the radicals R1-R2 may also be joined to R17-R19 to form a ring,

are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22- aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, halogen, NR202, OR20, SiR213, where the organic radicals R17-R19 may also be substituted by halogens and/or two vicinal radicals R17-R19 may also be joined to form a five-, six- or seven-membered ring, and/or two radicals R17-R19 are joined to form a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S,

the radicals R -βn . are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR213, where the organic radicals R20 may also be substituted by halogens and two radicals R20 may also be joined to form a five- or six-membered ring, and

the radicals C2-C22-alkenyl, C6-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part and two radicals R21 may also be joined to form a five- or six-membered ring,

u is 0 when E2-E4 is nitrogen or phosphorus and is 1 when E2-E4 is carbon,

R22-R31 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, halogen, NR322, OR32, SiR333, where the organic radicals R22-R31 may also be substituted by halogens and/or two vicinal radicals R22-R31 may also be joined to form a five-, six- or seven-mem bered ring, and/or two vicinal radicals R22-R31 are joined to form a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S,

the radicals R32 are each, independently of one another, hydrogen, CrC22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, SiR333, where the organic radicals R32 may also be substituted by halogens or nitrogen- and oxygen-containing groups and two radicals R32 may also be joined to form a five- or six-membered ring, and

the radicals R33 are each, independently of one another, hydrogen, C1-C2CTaIkVl, C2-C20-alkenyl, C6-C20-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, where the organic radicals R33 may also be substituted by halogens or nitrogen- and oxygen-containing groups and two radicals R33 may also be joined to form a five- or six-membered ring.

The three atoms E2to E4 in a molecule can be identical or different. E2to E4 are each nitrogen or carbon, in particular carbon.

The substituents R1-R2 can be varied within wide ranges. Possible carboorganic substituents R1C- R3Cand R8C-R17C are, for example, the following: CrC22-alkyl which may be linear or branched, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl or n-dodecyl, 5- to 7-membered cycloalkyl which may in turn bear a Cr C10-alkyl group and/or C6-C10-aryl group as substituent, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclododecyl, C2-C22-alkenyl, which may be lin- ear, cyclic or branched and in which the double bond may be internal or terminal, e.g. vinyl, 1- allyl, 2-alIyl, 3-allyl, butenyl, pentenyl, hexenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl or cyclooctadienyl, C6-C22-aryl which may bear further alkyl groups as substituents, e.g. phenyl, naphthyl, biphenyl, anthranyl, o-, m-, p-methylphenyl, 2,3-, 2,4-, 2,5- or 2,6-dimethylphenyl, 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6- or 3,4,5-trimethylphenyl, or arylalkyl, which may bear further alkyl groups as substituents, e.g. benzyl, o-, m-, p-methylbenzyl, 1- or 2-ethylphenyl, where, if appro- priate, a radical R1 to R2 may be joined to R17-R19 to form a 5-, 6- or 7-membered ring and/or the radicals R1-R2 may be joined to the radicals R17-R19 to form a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S and/or the organic radicals R1-R2 may also be substituted by halogens such as fluorine, chlorine or bromine. Furthermore, R1-R2 may be substituted by amino NR52, for example dimethylamino, N-pyrrolidinyl, picolinyl, by alkoxy or aryloxy OR5, e.g. methoxy, ethoxy or isopropoxy, or by SiR63, e.g. trimethyl- silyl, triethylsilyl, butyldimethylsilyl, tributylsilyl, tri-tert-butylsilyl, triallylsilyl, triphenylsilyl or dimethylphenylsilyl. Possible substituents R5 are the same carboorganic radicals as described in more detail above for R1-R2, where, if appropriate, two radicals R5 may be joined to form a 5- or 6- membered ring and/or be substituted by halogen. Possible radicals R6 for organosilicon substitu¬ ents SiR63 are the same carboorganic radicals as described in more detail above for R1-R2, where, if appropriate, two radicals R6 may also be joined to form a 5- or 6-membered ring.

Preferred radicals R1-R2 are hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert- butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, benzyl or phenyl.

The substituents R17-R19, too, can be varied within wide ranges. Possible carboorganic substitu¬ ents R17-R19 are, for example, the following: d-C22-alkyl which may be linear or branched, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n- nonyl, n-decyl or n-dodecyl, 5- to 7-membered cycloalkyl which may in turn bear a CVCio-alkyl group and/or C6-C10-aryl group as substituents, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclo- hexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclododecyl, C2-C22-alkenyl, which may be linear, cyclic or branched and in which the double bond may be internal or terminal, e.g. vinyl, 1-allyl, 2- allyl, 3-allyl, butenyl, pentenyl, hexenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl or cyclooctadi- enyl, C6-C22-aryl which may bear further alkyl groups as substituents, e.g. phenyl, naphthyl, bi- phenyl, anthranyl, o-, m-, p-methylphenyl, 2,3-, 2,4-, 2,5- or 2,6-dimethylphenyl, 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6- or 3,4,5-trimethylphenyl, or arylalkyl, which may bear further alkyl groups as substituents, e.g. benzyl, o-, m-, p-methylbenzyl, 1- or 2-ethylphenyl, here, if appropriate, two R17 to R19 may also be joined to form a 5-, 6- or 7-membered ring and/or two of the radicals R17-R19 may be joined to form a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S and/or the organic radicals R17-R19 may also be substi¬ tuted by halogens such as fluorine, chlorine or bromine. Furthermore, R17-R19 can be amino NR202, for example dimethylamino, n-pyrrolidinyl or picolinyl, alkoxy or aryloxy OR20, such as methoxy, ethoxy or isopropoxy or halogens such as fluorine, chlorine or bromine. Possible radi- cals R21 for organosilicon substituents SiR213 are the same carboorganic radicals mentioned in more detail above for R17-R19, where, if appropriate, two R21 may also be joined to form a 5- or 6- membered ring, e.g. trimethylsilyl, triethylsilyl, butyldimethylsilyl, tributylsilyl, tri-tert-butylsilyl, trial¬ lylsilyl, triphenylsilyl or dimethylphenylsilyl. Preferred radicals R17-R19 are hydrogen, methyl, trifluoromethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, benzyl, phenyl, fluorine, chlorine and bro¬ mine.

Possible carboorganic substituents R22-R31 are, for example, the following: C1-C22-alkyl which may be linear or branched, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl or n-dodecyl, 5- to 7-membered cycloalkyl which may in turn bear a CVC-io-alkyl group and/or C6-C10-aryl group as substituent, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclododecyl, C2-C22-alkenyl, which may be linear, cyclic or branched and in which the double bond may be internal or terminal, e.g. vinyl, 1-allyl, 2-allyl, 3-allyl, butenyl, pentenyl, hexenyl, cyclopentenyl, cyclohexenyl, cyclooctenyl or cyclooctadienyl, C6-C22-aryl which may bear further alkyl groups as substituents, e.g. phenyl, naphthyl, biphenyl, anthranyl, o-, m-, p-methylphenyl, 2,3-, 2,4-, 2,5- or 2,6-dimethylphenyl, 2,3,4-, ■2,3,5-, 2,3,6-, 2,4,5-, 2,4,6- or 3,4,5-trimethylphenyl, or arylalkyl, which may bear further alkyl groups as substituents, e.g. benzyl, o-, m-, p-methylbenzyl, 1- or 2-ethylphenyl, here, if appropri¬ ate, two R22 to R31 may also be joined to form a 5-, 6- or 7-membered ring and/or two of the radi¬ cals R22-R31 may be joined to form a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S and/or the organic radicals R22-R31 may also be substituted by halogens such as fluorine, chlorine or bromine. Furthermore, R22-R31 can be amino NR322, for example dimethylamino, n-pyrrolidinyl or picolinyl, alkoxy or aryloxy OR32, such as methoxy, ethoxy or isopropoxy or halogens such as fluorine, chlorine or bromine. Possible radicals R33 for organosilicon substituents SiR333 are the same carboorganic radicals mentioned in more detail above for R22-R31, where, if appropriate, two R33 may also be joined to form a 5- or 6- membered ring, e.g. trimethylsilyl, triethylsilyl, butyldimethylsilyl, tributylsilyl, tri-tert-butylsilyl, trial- lylsilyl, triphenylsilyl or dimethylphenylsilyl. Preference is given to at least one radical R22-R31 be¬ ing halogen such as fluorine, chlorine, bromine or iodine.

Preferred radicals R22-R31 are hydrogen, methyl, trifluoromethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, benzyl, phenyl, fluorine, chlorine, bromine and iodine. In particular, R22 to R25, R27 and R30 are each methyl, trifluoromethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, fluorine, chlorine or bro¬ mine and R26, R28, R29 and R31 are each hydrogen. R22 and R24 are particularly preferably each halogen such as fluorine, chlorine or bromine.

In particular, R22 and R24 are identical, R23 and R25 are identical, R26 and R29 are identical, R27 and R30 are identical and R28 and R31 are identical. This is also preferred in the preferred embodiments described further above.

Particularly preferred diimine compounds of the formula IV are 2,6-diacetylpyridinebis(2,6- dimethylphenylimine), 2,6-diacetylpyridinebis(2,4,6-trimethylphenylimine), 2,6- diacetyIpyridinebis(2-chloro-6-methylphenyl), 2,6-diacetylpyridinebis(2,6-diisopropylphenylimine), 2,6-diacetylpyridinebis(2,6-dichlorophenylimine), 2,6-pyridinedicarboxaldehydebis(2,6-diisopropyl- phenylimine), diacetylpyridinebis(2,6-dichlorophenylimine), diacetylpyridinebis(2,6- difluorphenylimine), diacetylpyridinebis(2,6-dibromophenylimine).

Primary amines used here are

which are preferably identical. The meanings of the variables and their preferred embodiments are the same as those described above for the diimine compound IV.

The molar ratio of the dicarbonyl compound and the primary amine used is generally from 1 :10 to 1 :1.8, preferably from 1 :5 to 1 :2 and particularly preferably from 1 :3 to 1 :2. The order of addition of individual components is not critical. Thus, for example, the dicarbonyl compound can be initially charged and the primary amine can be added thereto.

The phosphorus pentoxide can be used as a pure substance or else as a mixture with an inert solid such as aluminum oxide, silica gel or aiuminosilicate. Such mixtures are commercially avail- able under the tradename Sicapent. The molar ratio of dicarbonyl compound to phosphorus pen¬ toxide is preferably in the range from 1 :0.1 to 1 :100, preferably from 1 :1 to 1 :10 and particularly preferably from 1 :1.5 to 1 :3. The ratio of Sicapent (about 50% by weight water uptake capacity) to dicarbonyl compound is preferably in the range from 1 g of Sicapent per 0.1 mmol of dicarbonyl compound to 1 g of Sicapent per 100 mmol of dicarbonyl compound, more preferably from 1 g of Sicapent per 1 mmol of dicarbonyl compound to 1 g of Sicapent per 10 mmol of dicarbonyl com¬ pound and particularly preferably from 1 g of Sicapent per 1.8 mmol of dicarbonyl compound to 1 g of Sicapent per 6 mmol of dicarbonyl compound.

The order of addition of the phosphorus pentoxide is not critical, but it is preferably added to the mixture of dicarbonyl compound and primary amine. The total amount of phosphorus pentoxide used can be added at the beginning of the reaction, or it can be added in a number of portions during the ongoing reaction. It has been found that the process proceeds particularly quickly when the total amount of phosphorus pentoxide is added at the beginning of the reaction. As solvents, use is usually made of anhydrous aprotic solvents such as ethers or hydrocarbons. Suitable solvents include ethers such as diethyl ether, dibutyl ether, tetrahydrofuran or ethylene glycol ethers and aromatic and aliphatic hydrocarbons such as benzene, toluene, ethylbenzene, n-pentane, n-hexane, m-hexane, isohexane, n-heptane, n-octane, and also mixtures thereof. Pref- erence is given to using ethers and in particular tetrahydrofuran.

It has been found to be advantageous, particularly in the preparation of diimine compounds hav¬ ing halogen-containing substituents on the primary amine, to carry out the synthesis under a pro¬ tective gas atmosphere such as nitrogen or argon.

The reaction is generally carried out at from 18 to 1500C, preferably from 30 to 1100C and particu¬ larly preferably from 50 to 90°C. The reaction time is usually in the range from 30 minutes to 15 days, preferably from 5 hours to 5 days, particularly preferably from 8 hours to 3 days.

The work-up is carried out in a customary fashion, e.g. by removal of the solvent under reduced pressure. The product obtained can subsequently be purified by conventional methods, for exam¬ ple by means of chromatography of recrystallization.

The diimine compound obtained in this way can be used for the synthesis of transition metal com- plexes, for example iron complexes.

The process can also be used in modified form for the synthesis of diimine compounds from car- bonyl-imino compounds. Since the 2nd step in particular in the formation of the diimino compounds often gives low yields, the reaction of carbonyl-imino compound with primary imines in the pres- ence of phosphorus pentoxide to form diimines is a further process according to the invention. The definition of the primary amines and the reaction conditions are the same as those given above. The molar ratio of the carbonyl-iminq compound to the primary amine used is generally from 1 :5 to 1 :0.9, preferably from 1 :2 to 1 :1 and particularly preferably from 1 :1.2 to 1 :1. The mo¬ lar ratio of carbonyl-imino compound to phosphorus pentoxide is preferably in the range from 1 :0.1 to 1 :50, preferably from 1 :0.5 to 1 :5 and particularly preferably from 1 :1 to 1 :2. The ratio of Sicapent (about 50% by weight water uptake capacity) to carbonyl-imino compound is preferably in the range from 1 g of Sicapent per 0.1 mmol of carbonyl-imino compound to 1 g of Sicapent per 50 mmol of carbonyl-imino compound, more preferably from 1 g of Sicapent per 0.5 mmol of car¬ bonyl-imino compound to 1 g of Sicapent per 5 mmol of carbonyl-imino compound and particularly preferably from 1 g of Sicapent per 1 mmol of carbonyl-imino compound to 1 g of Sicapent per 3 mmol of carbonyl-imino compound.

In the process of the invention, a carbonyl-imino compound is any compound which contains at least one keto group, -C=O which is not part of a heteroaromatic ring, with aldehyde groups also being included here, and which contains at least one imine group -C=N- which is not part of a heteroaromatic ring.

Preference is given to using carbonyl-imino compounds of the formula Vl

where the variables have the following meanings: R1-R3 are each, independently of one another, hydrogen, 0!-022-SlKyI, C2-C22-alkenyl, C6-C22- aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part, NR52, or a five-, six- or seven-membered heterocycle containing at least one atom from the group consisting of N, P, O and S, where the organic radicals R1-R4 may also be substituted by halogens, NR52, OR5 or SiR63 and/or two radicals R1-R4 may also be joined with one another or with A to form a ring,

the radicals R are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22-aryl, alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part or SiR63, where the organic radicals R5 may also be substituted by halogens and two radicals R5 may also be joined to form a five- or six-membered ring, and

the radicals R6 are each, independently of one another, hydrogen, C2-C22-alkenyl, C3-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 car¬ bon atoms in the aryl part and two radicals R6 may also be joined to form a five- or six- membered ring,

m is 0 or 1 ,

i n ± 10 or a heteroaromatic ring system, where

L1-L2 are each, independently of one another, silicon or germanium,

R7-R15 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22- aryl, alkylaryl having from 1 to 10 carbon atoms in the aikyl part and 6-20 carbon atoms in the aryl part or SiR163, where the organic radicals R7-R15 may also be substituted by halogens and two radicals R7-R15 may also be joined to form a five- or six-membered ring, and

the radicals R16 are each, independently of one another, hydrogen, C1-C22-alkyl, C2-C22-alkenyl, C6-C22-aryl or alkylaryl having from 1 to 10 carbon atoms in the alkyl part and 6-20 carbon atoms in the aryl part and two radicals R16 may also be joined to form a five- or six- membered ring.

In this process, preference is likewise given to preparing diimine compounds of the formula I using primary amines R4NH2. The preferred embodiments of the variables are the same as those de¬ scribed above. This latter process is particularly useful for preparing diimine compounds having different radicals R3 and R4. The carbonyl-imino compound can be prepared by means of the customary synthetic methods, for example reaction of the dicarbonyl compound with p- toluenesulfonic acid in toluene.

The process of the invention allows, in particular, even primary amines having electron- withdrawing substituents to be converted into the corresponding diimine compounds in high yields. Furthermore, the time in which the conversion to the diimine proceeds to completion is significantly reduced.

A further advantage is that the process is also very suitable for producing commercial amounts. Amounts of 2 -200 kg of the diimine compound can be prepared without problems. In contrast, when molecular sieves are used, these are often attacked during stirring and then lead to prob¬ lems in the work-up.

The following experimental examples serve to illustrate the invention without implying any restric¬ tion of the scope of the invention.

Examples

Example 1 Preparation of 2,6-diacetylpyridinebis(2,4-dichloro-6-methylphenylanil) 45 g of 2,6-diacetylpyridiπe (0.276 mol), 106.8 g of 2,4-dichloro-6-methylaniline (0.607 mol) and 28 g of Sicapent were heated under reflux in 1200 ml of tetrahydrofuran for 7.5 hours and stirred under argon for a further 12 hours at room temperature. A further 28 g of Sicapent were added and the mixture was refluxed for another 10.5 hours and stirred for a further 13 hours at room temperature. The GC/MS indicates a yield of 86% of the product. The insoluble solid is filtered off and washed with tetrahydrofuran. The solvent was distilled off from the filtrate obtained in this way, the residue was admixed with 500 ml of methanol and subsequently stirred at 550C for one hour. The suspension formed in this way was filtered and the solid obtained was washed with methanol and freed of the solvent. The filtrate was freed of the solvent once again and taken up in 200 ml of methanol and admixed with a seed crystal. The product obtained in this way was filtered off and washed with methanol. This procedure was repeated on the filtrate obtained in this way. The combined product was taken up in 800 ml of methanol, stirred for one hour, filtered and the • solid was washed with ether. This gave 101.8 g of 2,6-diacetylpyridinebis(2,4-dichloro-6- methylphenylanil) in a yield of 77%.

Example 2 Preparation of 2,6-diacetylpyridinebis(2,4-dichloro-6-methylphenyIanil) 22.5 g of 2.6-diacetylpyridine (0.138 mol), 53.39 g of 2,4-dichloro-6-methylaniline (0.303 mol) and 64 g of Sicapent were refluxed in 500 ml of tetrahydrofuran under argon for 18 hours and the mix- ture was subsequently cooled to room temperature. The GC/MS indicates a yield of 91.5% of the product. The work-up was carried out as described in Example 1. This gave 2,6-diacetyI- pyridinebis(2,4-dichloro-6-methylphenylanil) in a yield of 81 %.

Example 3 Preparation of 2,6-diacetylpyridinebis(2,4-dichloro-6-methylphenyIanil) 4 g of 2,6-diacetylpyridine (0.025 mol), 9.49 g of 2,4-dichloro-6-methylaniline (0.054 mol) and 8.5 g of phosphorus pentoxide were refluxed in 90 ml of tetrahydrofuran for 26 hours and stirred under argon for a further 12 hours at room temperature. The GC/MS indicates a yield of 87.3% of the product. The work-up was carried out as described in Example 1. This gave 2,6- diacetylpyridinebis(2,4-dichloro-6-methylphenylanil) in a yield of 65%.

Comparative Example Preparation of 2,6-diacetylpyridinebis(2,4-dichloro-6-methylphenylanil) by the method of Qian et al., Organometallics 2003, 22, 4312-4321.

65.6 g of 2,6-diacetylpyridine (0.4 mol), 170 g of 2,4-dichloro-6-methylaniline (0.483 mol), 32 g of Al-Si silica gel grade 135 and 160 g of molecular sieves (4A) were stirred in 1500 ml of toluene at 8O0CjOr 5 hours and.a further 32 g_ of silica gel grade 135 and _160_g ofjnolecular sieves (4A)__ were subsequently added. The mixture was stirred at 8O0C for another 8 hours (the GC/MS indi- cates a yield of 64% of the product), the insoluble solid was filtered off and washed twice with toluene. The solvent was distilled off from the filtrate obtained in this way, the residue was ad¬ mixed with 200 ml of methanol and subsequently stirred at 55°C for 1 hour. The suspension formed in this way was filtered and the solid obtained was washed with methanol and freed of the solvent. This gave 95 g of 2,6-diacetylpyridinebis(2,4-dichloro-6-methylphenylanil) in a yield of 47%.