Abstract:
The invention relates to novel transition metal complexes containing at least one diaminocarbene ligand, to processes for preparing these transition metal complexes and to their use as catalysts in organic reactions.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to novel transition metal complexes containing at least one diaminocarbene ligand, to processes for preparing these transition metal complexes and to their use as catalysts in organic reactions.  
           [0003]    2. Brief Description of the Prior Art  
           [0004]    Transition metal-carbene complexes have been known for a long time and are important reagents in the field of synthetic organic chemistry. Transition metal-carbene complexes are used, inter alia, as catalysts in organic reactions.  
           [0005]    In Synth. Meth. Organomet. Inorg. Chem. 9, 2000, 84-112, Herrmann et al. describe N-heterocyclic transition metal-carbene complexes and use, for example, palladium(0)-carbene complexes as catalysts for Heck reactions and state that Ru(II)-carbene complexes are promising catalysts for reactions involving C—C or C—H bond formation.  
           [0006]    WO 00/15339 A1 describes carbene complexes of ruthenium and of osmium which can be used as catalysts in olefin metathesis.  
           [0007]    Despite the fact that transition metal-carbene complexes suitable as catalysts in organic synthetic reactions are known, there is a need for new transition metal-carbene complexes which can be used, in particular, as catalysts in organic synthetic reactions and have not only high activities but also long catalyst operating lives so that they can be used in large-scale industrial syntheses.  
         SUMMARY OF THE INVENTION  
         [0008]    We have now surprisingly found compounds of the general structural formula (I),  
                         
 
           [0009]    where  
           [0010]    M is a transition metal of transition groups 6 to 8 of the Periodic Table,  
           [0011]    the radicals R 1 , R 2 , R 3  and R 4  are identical or different and are hydrogen and/or hydrocarbon groups, where the hydrocarbon groups may be identical or different, straight-chain, branched or cyclic radicals selected from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having from 2 to 50 carbon atoms, alkynyl radicals having from 2 to 50 carbon atoms and aryl radicals having from 6 to 30 carbon atoms in which at least one hydrogen atom may be replaced by a functional group, and/or  
           [0012]    R 1  and R 2  and/or R 3  and R 4  are part of a cyclic system which is identical or different, where the cyclic system comprises a carbon framework having from 2 to 20 carbon atoms and a nitrogen atom in formula (I), where the carbon atoms of R 1  and R 2  and/or R 3  and R 4  in formula (I) are not counted and where at least one hydrogen atom in the ring may be replaced by a functional group and/or at least one carbon atom of the ring may be replaced by a heteroatom selected from the group consisting of S, P, O and N, and/or  
           [0013]    R 1  and/or R 2  and/or R 3  and/or R 4  are linked to one of the ligands L via a bridge having from 1 to 20 carbon atoms, where the carbon atoms of R 1 , R 2  R 3  and R 4  are not counted, and  
           [0014]    L are identical or independently different uncharged two-electron donors and/or are parts of a cyclic system and/or are anionic ligands, and  
           [0015]    n is an integer, preferably from 0 to 6, particularly preferably from 2 to 4.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0016]    The compounds of the invention have at least one diaminocarbene ligand of the type R 1 R 2 N—C—NR 3 R 4  as a structural feature and possess surprisingly long catalyst operating lives. This advantage is particularly evident in reactions which proceed in the temperature range above 100° C. The compounds of the invention also have extraordinary thermal stabilities and a high catalyst activity.  
           [0017]    If L in the novel compounds of the general formula (I) represents identical or independently different uncharged two-electron donors, the ligands in question are preferably ligands selected from the group consisting of amines, imines, phosphines, phosphites, stibines, arsines, CO, carbonyl compounds, nitrites, alcohols, thiols, ethers, thioethers and pyridines.  
           [0018]    Furthermore, L preferably represents identical or independently different uncharged two-electron donor ligands selected from the group consisting of N-heterocyclic carbenes of the general formulae (A-E)  
                         
 
           [0019]    where  
           [0020]    the radicals R 5 , R 6 , R 7  and R 8  are identical or different and are hydrogen and/or hydrocarbon groups, where the hydrocarbon groups are identical or different, straight-chain, branched or cyclic radicals selected from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having from 2 to 50 carbon atoms, alkynyl radicals having from 2 to 50 carbon atoms and aryl radicals having from 6 to 30 carbon atoms in which at least one hydrogen atom may be replaced by a functional group, and/or  
           [0021]    the radicals R 6  and R 7  are identical or independently different halogen, nitro, nitroso, alkoxy, aryloxy, amido, carboxyl, carbonyl, thio or/and sulfonyl groups.  
           [0022]    Furthermore, L preferably represents identical or independently different uncharged two-electron donor ligands selected from the group consisting of diaminocarbene ligands of the general formula (II),  
                         
 
           [0023]    where  
           [0024]    the radicals R 1 , R 2 , R 3  and R 4  are as defined above.  
           [0025]    Furthermore, L preferably represents identical or independently different uncharged two-electron donor ligands selected from the group consisting of compounds of the general formulae (III) and (IV)  
                         
 
           [0026]    where  
           [0027]    the radicals R 9  and R 10  are identical or different and are hydrogen or/and hydrocarbon groups, where the hydrocarbon groups are identical or different, straight-chain, branched or cyclic radicals selected from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having from 2 to 50 carbon atoms, alkynyl radicals having from 2 to 50 carbon atoms, aryl radicals having from 6 to 30 carbon atoms and silyl radicals in which at least one hydrogen atom may be replaced by an alkyl, aryl, alkenyl, alkynyl, metallocenyl, halogen, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio or/and sulfonyl group.  
           [0028]    If L in the novel compounds of the general formula (I) is part of a cyclic system, the cyclic system is preferably a cyclic diene, preferably a diene having from 5 to 10 carbon atoms, very particularly preferably 1,5-cyclooctadiene.  
           [0029]    If L in the novel compounds of the general formula (I) represents identical or independently different anionic ligands, the ligands concerned are preferably ligands selected from the group consisting of halides, pseudohalides, hydroxides, alkoxides, thiolates, carboxylates and sulfonates, with preferred pseudohalides being cyanide, thiocyanate, cyanate, isocyanate and isothiocyanate.  
           [0030]    In a preferred embodiment of the novel compounds of the general formula (I), M is rhodium or iridium and n is 3, with L 1 , L 2  and L 3  being identical or independently different and/or being part of a cyclic system, where  
           [0031]    L 1  is an anionic ligand selected from the group consisting of halide, alkoxide, carboxyl compound, thiolate and pseudohalide or is an uncharged two-electron donor selected from the group consisting of alkenes, alkynes, phosphines, amines, imines, phosphites, stibines, arsines, CO, carbonyl compounds, nitriles, alcohols, ethers, thiols and thioethers and  
           [0032]    L 2  and L 3  are identical or independently different and are uncharged two-electron donor ligands selected from the group consisting of alkenes, alkynes, phosphines, amines, imines, phosphites, stibines, arsines, CO, carbonyl compounds, nitriles, alcohols, ethers, thiols and thiolethers or, in a preferred embodiment, are part of a cyclic diene; particular preference is given to L 2  and L 3  together representing 1,5-cyclooctadiene.  
           [0033]    In a particularly preferred embodiment of the novel compounds of the general formula (I) M is rhodium or iridium and n is 3 and L 2  and L 3  together represent a cyclic diene, very particularly preferably 1,5-cyclooctadiene, and L 1  is halide or CO, with the charge on monovalent or trivalent rhodium or iridium being balanced and the resulting coordination numbers being 4, 5 or 6.  
           [0034]    In a further preferred embodiment of the novel compounds of the general formula (I), M is ruthenium or osmium and n is 4 and  
           [0035]    L 1  and L 2  are identical or independently different and are each an anionic ligand selected from the group consisting of halide, alkoxide, carboxyl compound, thiolate and pseudohalide, with preferred pseudohalides being cyanide, thiocyanate, cyanate, isocyanate and isothiocyanate,  
           [0036]    L 3  is a carbene ligand of the general formula (III) or (IV) and  
           [0037]    L 4  is an uncharged two-electron donor ligand selected from the group consisting of amines, imines, phosphines, phosphites, stibines, arsines, CO, carbonyl compounds, nitriles, alcohols, thiols, ethers and thioethers or is an uncharged two-electron donor selected from the group consisting of N-heterocyclic carbenes of the general formulae A-E or a diaminocarbene ligand of the general formula (II).  
           [0038]    If L 4  is a diaminocarbene ligand of the general formula (II), then R 1  and R 2  and/or R 3  and R 4  are preferably part of a cyclic system comprising a carbon framework having from 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, and a nitrogen atom in formula (II), with the carbon atoms of R 1  and R 2  and/or R 3  and R 4  in formula (II) not being counted and at least one hydrogen atom in the ring being able, if desired, to be replaced by a functional group. In the event of more than one such cyclic system, these may be identical or different.  
           [0039]    In a further, particularly preferred embodiment of the novel compounds of the general formula (I), M is ruthenium or osmium and n is 4 and L 1  and L 2  are identical or different and are each chloride, bromide or iodide, L 3  is a carbene ligand of the general formulae (III) or (IV) and L 4  is a phosphine, preferably trimethylphosphine, tricyclohexylphosphine or triphenylphosphine, and are chosen so that the charge on the divalent, tetravalent or hexavalent ruthenium or osmium is balanced and the resulting coordination number is 4, 5 or 6.  
           [0040]    In a further, preferred embodiment of the novel compounds of the general formula (I), M is Cr and n is 4 and the ligands L 1  to L 4  are identical or different and are uncharged two-electron donor ligands such as CO, phosphine, phosphite, stibine, arsine, alkene, alkyne, amine, imine, carbonyl compounds, nitrile, alcohol, ether, thiol, thioether or nitrile; it is very particularly preferred that L 1  to L 4  are identical and are each CO.  
           [0041]    Various methods known from the literature for the preparation of transition metal complexes with saturated or unsaturated N-heterocyclic carbene ligands are in principle available for the synthesis of the compounds of the invention. Such methods include reaction of suitable transition metal precursors with the free ligands of the type R 1 R 2 N—C—NR 3 R 4  which can be prepared from the corresponding formamidinium salts [R 1 R 2 N—CH═NR 3 R 4 ] + X −  or with the formamidinium salts themselves (salt metathesis). These methods were applied successfully to diaminocarbene ligands for the first time in the present invention. The novel compounds of the formula (I) concerned were not expected to be stable systems according to the prior art.  
           [0042]    To prepare novel compounds of the formula (I) in a ligand exchange reaction via free carbene, preference is given to reacting the free carbene ligand of the general formula (II) with suitable transition metal complexes, with the free carbene being prepared from the formamidinium salt by deprotonation with strong bases such as lithium diisopropylamide (Angew. Chem. 1996,108, 1211; Angew. Chem Int. Ed. Engl. 1996, 35, 1121; Tetrahedron 1999,55 14523-14534), but particularly preferably by the “ammonia method” described in DE 196 10 908 A1.  
           [0043]    To prepare the novel compounds of the formula (I) by salt metathesis, the formamidinium salts are reacted with suitable transition metal complexes.  
           [0044]    However, it is also possible to generate the carbene of the general formula (II) in situ as an intermedium from the alkoxide adduct of the formamidinium salt with alkali metal alkoxides, preferably potassium tert-butoxide, by brief heating. This intermediate then undergoes a ligand exchange reaction with appropriate transition metal complexes to form the compounds of the invention (WO 00/71554 A2 and WO 00/15339 A1).  
           [0045]    The preparation of the novel compounds of the formula (I) is preferably carried out by the following methods:  
           [0046]    a) Ligand Exchange Reaction via Free Carbene:  
                         
 
           [0047]    L′ is preferably an uncharged exchange ligand such as nitrile or phosphine. The ligand exchange reaction is preferably used for the preparation of the novel compounds of the formula (I) in which M is ruthenium or osmium.  
           [0048]    b) Salt Metathesis:  
                         
 
           [0049]    Y is preferably an uncharged or anionic exchange ligand, for example, amine, halide, acetate, acetylacetonate or alkoxide. Salt metathesis is preferably used for the preparation of the novel compounds of the formula (I) in which M is rhodium or iridium.  
           [0050]    c) Alkoxide Adduct Method (Generation of the Carbene in situ):  
                         
 
           [0051]    L′ is preferably an uncharged exchange ligand such as nitrile or phosphine. The ligand exchange reaction is preferably used for the preparation of the novel compounds of the formula (I) in which M is ruthenium or osmium.  
           [0052]    The compounds of the invention are preferably used as catalysts in organic synthetic reactions, for example, as catalysts for hydrosilylation, hydroformylation, olefin metathesis, alkyne metathesis, Heck coupling, Suzuki coupling, Sonogashira coupling, cyclopropanation or Grignard cross-coupling. Preference is given to using novel compounds of the formula (I) in which M is ruthenium or osmium in olefin metathesis. Further preference is given to using novel compounds of the formula (I) in which M is rhodium or iridium in hydrosilylation. The compounds of the invention can be used both as homogeneous catalysts and as heterogeneous catalysts. The latter embodiment is preferably achieved by the compounds of the invention being bound to a solid phase, for example, a polymeric support. The compounds of the invention are preferably bound to the solid phase via one or more ligands L, preferably via a ligand L selected from the group consisting of N-heterocyclic carbenes of the general formulae A-E and/or via a diaminocarbene ligand of the general formula (II).  
           [0053]    The compounds of the invention are highly active and particularly inexpensive catalysts which can be synthesized in good yield. Furthermore, the catalytic activity and selectivity of the compounds of the present invention can be controlled via the wide variety of possible ligand spheres, especially by variation of the diaminocarbene ligand R 1 R 2 N—C—NR 3 R 4 .  
           [0054]    The advantage of these novel complexes compared with phosphine-containing or/and mixed phosphine-/N-heterocyclic carbene-containing complexes is the inexpensive preparation of the diaminocarbene ligands. The stability, selectivity and activity of the catalysts can be increased significantly compared with existing systems.  
       
    
    
     EXAMPLES  
       [0055]    The following examples illustrate the invention, but do not restrict its scope.  
       Example 1  
     Precursors for Preparing the Complexes of the Invention  
       [0056]    Tetramethylformamidinium chloride is commercially available. Tetraisopropylformamidinium chloride was synthesized by the method described in Angew. Chem. 1996,108,1211 and Angew. Chem. Int. Ed. Engl., 1996, 35,1121.  
         [0057]    a) Preparation of Dipiperidylformamidinium Chloride:  
         [0058]    6.08 g (0.05 mol) of piperidinium chloride, 4.26 g (0.05 mol) of piperidine and 7.41 g (0.05 mol) of triethyl orthoformate were refluxed in 25 ml of ethanol for 4 hours. After cooling overnight, the volatile constituents were removed in a high vacuum. The residue was washed with 20 ml of THF (tetrahydrofuran) and subsequently extracted with 100 ml of a mixture of 20% by volume of ethanol and 80% by volume of ethyl acetate. The extract was dried over magnesium sulfate. Removal of the solvent in a high vacuum gave dipiperidylformamidinium chloride as a slightly yellowish, very hygroscopic solid.  
         [0059]    [0059] 1 H NMR (CDCl 3 , 25° C.): δ=7.94 (1H, s, NCHN), 3.03, 3.36 (8H, m, NCH 2 ), 1.5-0.91 (m, 12H, residual CH 2 ).  
         [0060]    [0060] 13 C NMR (CDCl 3 , 25° C.): δ=154.3 (NCHN), 51.9, 44.4 (NCH 2 ), 25.5, 22.7, 22.2 (NCH 2 CH 2 CH 2 CH 2 CH 2 ).  
         [0061]    b) Preparation of Dipiperidylformamidinium Tetrafluoroborate  
         [0062]    5 ml (0.01 mol) of piperidine, 2.6 g (0.025 mol) of ammonium tetrafluoroborate and 40 ml of triethyl orthoformate were refluxed for 2 hours. Ethanol formed was distilled off. Two phases were formed during this time. After cooling, the lower yellow phase was taken up in methylene chloride and dried over magnesium sulfate. Removal of the solvent in a high vacuum gave dipiperidylformamidinium tetrafluoroborate as a slightly yellowish, very hygroscopic solid.  
       Example 2  
     Synthesis of the Free Carbenes  
       [0063]    a) Deprotonation with NaH/NH 3 (I) (Ammonia Method)  
         [0064]    10 mmol of the corresponding formamidinium chloride or tetrafluoroborate together with about 20 ml of THF were placed in a reaction vessel. After about 20 ml of ammonia had been condensed onto this, 11 mmol of NaH were added. A slightly yellowish solution was formed over the course of about 2 hours. Firstly the ammonia and then the THF were subsequently removed in a high vacuum and the free carbene was extracted with hexane. The solution obtained in this way can be directly used further.  
         [0065]    b) Deprotonation of the Formamidinium Salts With Lithium Diisopropylamide  
         [0066]    A solution of 10 mmol of the corresponding formamidinium chloride or tetrafluoroborate in 15 ml of THF was slowly added dropwise at −78° C. to a solution of 10 mmol of lithium diisopropylamide in 15 ml of THF. The solution was slowly warmed to room temperature over a period of two hours. This resulted in formation of a clear, slightly yellowish solution. The solvent was removed in a high vacuum. The residue was extracted three times with 15 ml each time of toluene. The solution obtained in this way is directly used further.  
       Example 3  
     Synthesis of the Complexes of the Invention  
       [0067]    a) Synthesis of the Rh/Ir Compounds by Means of a Ligand Exchange Reaction  
         [0068]    I) Chloro(η 4 -1,5-cyclooctadiene)(bis(diisopropylamino)carbene)rhodium(I)  
         [0069]    A solution of bis(diisopropylamino)carbene (340 mg, 1.71 mmol, 2 eq) in THF (20 ml) was added dropwise to a solution of bis[μ-chloro(1,5-cyclooctadiene)rhodium] (421 mg, 0.85 mmol, 1 eq) in 40 ml of THF. The colour changed from light yellow to dark yellow. After stirring at room temperature for 30 minutes, the solvent was removed under reduced pressure. The precipitate was washed with ice-cold diethyl ether (2×10 ml) and dried under reduced pressure. Yield: 533 mg, 71%.  1 H NMR (400 MHz, CDCl 3 , 20° C.): δ=5.16 (2H, cod vinyl ), 4.73 (1H, cod vinyl ), 4.09 (4H, NCH), 3.09 (1H, cod vinyl ), 2.35 (4H, cod allyl ), 1.74-1.17 (m, 28H, cod allyl , CH 3 ).  
         [0070]    [0070] 13 C{ 1 H} NMR (100.1 MHz, CDCl 3 , 20° C.): δ=233.6 (NCN, d,  1 J(C—Rh)=67.8 Hz), 97.5, 67.3, 32.5, 30.9, 28.6 (cod), 56.4 (NCH), 23.8 (CH 3 ). MS (Cl) m/e=458 (M + , correct isotope pattern), 423 (M-Cl, correct isotope pattern), 314 (M-Cl-cod, correct isotope pattern). Elemental analysis: (C 21 H 40 ClN 2 Rh, 458.92): calculated: C. 54.96, H. 8.78, N. 6.10; found: C. 54.90, H. 8.81, N. 6.17.  
         [0071]    II) Chloro(θ 4 -1,5-cyclooctadiene)(bisdiisopropylaminocarbene)iridium(I)  
         [0072]    Using a method analogous to that for the synthesis of the rhodium complex, bis[μ-chloro(1,5-cyclooctadiene)iridium(I)] (340 mg, 1.00 mmol, 1 eq) was reacted with bis(diisopropylamino)carbene (200 mg, 1.00 mmol, 2 eq) to form the desired complex. Yield: 746 mg, 68%.  
         [0073]    [0073] 1 H NMR (400 MHz, CDCl 3 , 20° C.): δ=5.13 (2H, cod vinyl ), 4.73 (2H, cod vinyl ), 3.85 (4H, NCH), 2.95 (4H, cod allyl ), 2.11 (m, 4H, cod allyl ), 1.58-1.17 (m, 24H, CH 3 ).  
         [0074]    [0074] 13 C{ 1 H} NMR (100.1 MHz, CDCl 3 , 20° C.): δ=225.6 (NCN), 82.1, 67.9, 33.2, 31.9, 29.2 (cod), 51.1 (NCH), 23.8 (CH 3 ).  
         [0075]    MS (Cl) m/e=548 (M + , correct isotope pattern).  
         [0076]    Elemental analysis: (C 21 H 40 ClN 2 Ir, 548.23), calculated: C. 46.01, H. 7.35, N. 5.11;found: C. 46.09, H. 7.41, N. 5.07.  
         [0077]    b) Synthesis of the Rh/Ir Complexes by Salt Metathesis  
         [0078]    I) Chloro(η 4 -1,5-cyclooctadiene)(bis(diisopropylamino)-carbene)rhodium(I)  
         [0079]    A 1 M solution of sodium methoxide (2.48 ml) was added dropwise to a suspension of bis[μ-chloro(1,5-cyclooctadiene)rhodium(I)] (300 mg, 0.61 mmol, 1 eq) in ethanol (30 ml). Over a period of 5 minutes, the color changed to lemon yellow owing to the formation of bis[μ-ethoxy(1,5-cyclooctadiene)rhodium(I)]. After stirring at room temperature for a further 10 minutes, bis(diisopropyl)formamidinium chloride (400 mg, 1.22 mmol, 2 eq) was added. The color changed to dark yellow. After stirring at room temperature for a further 30 minutes, the volatile constituents were removed under reduced pressure and the crude product was washed with ice-cold diethyl ether (2×10 ml) and dried. Yield: 531 mg, 68%.  
         [0080]    II) Chloro(η 4 -1,5-cyclooctadiene)(bisdiisopropylaminocarbene)iridium(I)  
         [0081]    Using a method analogous to Example 3b, 1), bis[μ-chloro(1,5-cyclooctadiene)iridium(I)] (333 mg, 0.61 mmol, 1 eq), 1M sodium methoxide solution (2.48 ml) and bis(diisopropyl)formamidinium chloride (400 mg, 2 eq) were reacted to form the desired iridium compound in a yield of 71%.  
         [0082]    c) Synthesis of the Rh/Ir Complexes via an Alkoxide Adduct  
         [0083]    I) Chloro(η 4 -1,5-cyclooctadiene)(bis(diisopropyl amino)-carbene)rhodium(I)  
         [0084]    A solution of potassium tert-butoxide (191 mg, 1.70 mmol, 2.8 eq) in THF (20 ml) was added dropwise to a suspension of bis(diisopropyl)formamidinium chloride (280 mg, 1.70 mmol, 2.8 eq) in THF (30 ml) at room temperature, resulting in the formamidinium chloride dissolving slowly and the color changing to light yellow. After stirring at room temperature for 30 minutes, bis[μ-chloro(1,5-cyclooctadiene)rhodium(I)] (300 mg, 0.61 mmol, 1 eq) and toluene (30 ml) were added. The reaction solution was stirred at 80° C. for 1 hour. The volatile constituents were then removed under reduced pressure and the desired product was extracted with 60 ml of hexane. Drying gave the complex in a yield of 73%.  
         [0085]    II) Chloro(η 4 -1,5-cyclooctadiene)(bis(diisopropylamino)-carbene)iridium(I)  
         [0086]    Using a method analogous to Example 3c, I), bis[μ-chloro(1,5-cyclooctadiene)-iridium(I)] (333 mg, 0.61 mmol, 1 eq), KOtBu (191 mg, 1.70 mmol, 2.8 eq) and bis(diisopropyl)formamidinium chloride (280 mg, 1.70 mmol, 2.8 eq) were reacted to form the desired iridium compound in a yield of 66%.  
         [0087]    d) Synthesis of a Cr Complex by Means of a Ligand Exchange Reaction  
         [0088]    I) Tetracarbonyl(bisdiisopropylaminocarbene)chromium(0)  
         [0089]    A solution of 390 mg (1.6 mmol) of Cr(CO) 6  in 50 ml of THF was irradiated by a mercury vapor lamp (150 W) at room temperature for 3.5 hours while stirring. 200 mg (0.94 mmol) of bis(diisopropylamino)carbene were dissolved in 5 ml of tetrahydrofuran and added dropwise to the orange solution while stirring vigorously. After stirring at room temperature for a further 30 minutes, the color of the reaction solution changed to reddish brown. The solvent was distilled off under reduced pressure and excess Cr(CO) 6  was removed by sublimation in high vacuum. The brown residue was extracted three times with 20 ml each time of diethyl ether, the combined extracts were evaporated to 5 ml and then chromatographed on a 50 cm×1.0 cm silica gel column made up using hexane. After a pale yellow zone had been eluted with hexane/diethyl ether (2:1) (contains mainly Cr(CO) 6 ), the product could be eluted as a dark yellow band by means of diethyl ether. The product fractions were evaporated to 1-2 ml under reduced pressure and, after addition of 5-10 ml of hexane, the chromium complex precipitated at 0° C. in the form of dark yellow crystals which could be recrystallized from diethyl ether/hexane. Yield: 80 mg (23%)  
         [0090]    [0090] 1 H-NMR (400.13 MHz, C 6 D 6 ): δ 0.942 (br. CH 3 , 24H), 2.961 (br, CH, 4H) IR (hexane, cm −1 ): ν=2003.8 (m, CO); 1918.4 (w, CO); 1896.3 (s, CO); 1870.1 (m, CO)  
         [0091]    Elemental analysis: C 17 H 28 CrN 2 O 4  C: 54.24; H: 7.50, N: 7.44 (calculated); C: 54.85; H: 7.39; N: 6.94 (found).  
         [0092]    The corresponding molybdenum and tungsten compounds were synthesized in an analogous manner from Mo(CO) 6  and W(CO) 6 .  
       Example 4  
     Preparation of dicarbonylchloro(bis(diisopropylamino)-carbene)rhodium(I) by Means of a Ligand Exchange Reaction  
       [0093]    Carbon monoxide was passed through a yellow solution of chloro(η 4 -1,5-cyclooctadiene)(bis(diisopropylamino)carbene)rhodium(I) (300 mg, 0.65 mmol) in a 1:1 mixture of THF and toluene (35 ml) for 30 minutes. After the reaction solution had become brownish in color, the solvent was removed under reduced pressure and the crude product was washed with n-pentane. Yield: 68%.  
         [0094]    [0094] 1 H NMR (400 MHz, CDCl 3 , 20° C.): δ=4.11 (4H, NCH), 1.36 (24H, CH 3 )  13 C{ 1 H} NMR (100.1 MHz, CDCl 3 , 20° C.): δ=221.7 (NCN, d,  1 J(C—Rh)=64 Hz), 186.9 (CO, d,  1 J(C—Rh)=74 Hz), 56.1 (NCH), 23.5 (CH 3 )  
         [0095]    MS (Cl) m/e=406 (M + , correct isotope pattern).  
         [0096]    IR (KBr, cm −1 ): ν=2056 (s, CO), 1985 (s, CO).  
         [0097]    Elemental analysis: (C 15 H 28 ClN 2 O 2 Rh, 406.76): calculated: C. 44.29, H. 6.93, N. 6.88; found: C. 44.32, H. 6.89, N. 6.91.  
       Example 5  
     Hydrosilylation of Acetophenone  
       [0098]    0.61 ml of a stock solution of starting material (consisting of 0.8 ml of acetophenone, 1.3 ml of diphenylsilane and 300 mg of ferrocene as internal standard dissolved in 4 ml of d 8 -THF) together with 1 mol % of chloro(η 4 -1,5-cyclooctadiene)(bis(diisopropylamino)carbene)rhodium(I) as catalyst (as stock solution, 0.2 ml of d 8 -THF) were placed in an NMR tube. After shaking vigorously, recording of the NMR kinetics was commenced immediately, with a  1 H NMR spectrum being recorded every 10 minutes. The conversion was determined by integration of the relevant proton signals. The results are shown in Table 1.  
                                                                           TABLE 1                           Hydrosilylation of acetophenone using various catalysts                Conversion of acetophenone [%]            Time [min]   KD2   KD1   iPr-BIM   Cy-IM                    0.0   0.0000   0.0000   0.0000   0.0000       1.5   2.1083   5.3043   16.5262   49.7128       11.5   10.2384   19.7991   22.2451   63.8878       21.5   18.3888   27.1516   36.1491   64.2819       31.5   22.2013   40.4057   51.9386   64.4957       41.5   26.4179   50.1740   62.4524   64.6827       51.5   33.0257   57.5527   68.3399   65.2572       61.5   38.2527   63.9139   72.6104   65.6246       71.5   43.7828   68.4960   75.0390   66.2191       81.5   48.1140   72.3495   77.5176   66.6333       91.5   53.3275   75.7369   79.2908   66.8270       101.5   57.5778   78.5466   80.7767   67.2545       111.5   61.1949   80.5160   82.0191   67.2612       121.5   63.8488   81.5992   82.8307   67.4349       131.5   66.3142   82.0259   83.6486   67.5618       141.5   66.6038   82.4526   84.1668   67.7355       151.5   68.8199   82.6626   84.6663   67.9225       161.5   70.5914   82.7677   85.0846   67.8156       171.5   72.6122   82.9121   85.3843   68.0227       181.5   72.1137   83.1287   85.7402   68.1496       191.5   74.4308   83.2994   85.8900   68.1764       201.5   76.6941   83.5554   86.0586   68.3901                                                                                                                                                                               
 
         [0099]    where COD is 1,5-cyclooctadiene, iPr is an isopropyl radical, Cy is a cyclohexyl radical and Mes is a mesityl radical.  
         [0100]    Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.