Title of Invention	A PROCESS FOR THE PREPARATION OF NOVEL RHODIUM METAL COMPLEXES
Abstract	A process for the preparation of novel rhodium metal complexes: The present invention provides a process for preparing rhodium(l) complexes containing different types of ligands facilitating high electron density on the rhodium center and consequently can act as efficient catalyst for carbonylation of methanol to acetic acid.

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The present invention relates to a process for the preparation of novel rhodium metal complexes. More particularly the present invention relates to a process for the preparation of novel rhodium(I) carbonyl or cyclooctadiene complexes containing tertiary phosphine chalcogenide or ether-phosphine or nitrogen donor ligands. Such rhodium metal complexes prepared by the process of the present invention may be useful as catalyst precursors for carbonylation of methanol to acetic acid or its ester. Mention may be made that Ainscough et. al. have reported ( J. Chem. Soc. Dalton Trans. 1973, 2167) the synthesis of [Rh(COD)ClL] (L = Me3PS, PhMe2PS and PhMe2PSe), but they did not show any catalytic application. Reference may be made that Bandoli et. al, reported (J. Organomet. Chem. 1974, 71, 125) a dicarbonyl complex [Rh(CO)2Cl(Cy3PO)], (Cy = tricyclohexyl) but they did not disclose any catalytic application. It may be mentioned that Kwaskowska et. al. ( Trans. Met. Chem. 1983, 8, 103) have reported a rhodium(I) dicarbonyl complex containing ortho - amino benzoic acid but no other analog reported so far. They did not report any catalytic application. Krylov et. al. (Zh. Obshch. Khim. 1991, 61(7), 1647 have synthesized rhodium(I) dicarbonyl complexes of aminophenol for which no catalytic applications was reported. Reference may be made to Lindner et. al. have reported (Organometallics, 1993, 12, 1865) cis and trans dicarbonyl cationic rhodium(I) complexes of dicyclohexyl (methoxy) ethyl phosphine (Cy2PCH2CH2OCH3) but they did not disclose any catalytic application. Anderson et. al. have reported (Inorg. Chim. Acta., 1988, 146, 89) a rhodium(I) complex containing cyclooctadiene and Ph2PCH2CH2OCH3 ligand but they did not disclose any catalytic application. Since the first report of catalysis by [Rh(CO)2I2]" (F. E. Paulik and J. F. Roth, J. Chem. Soc. Chem. Comm., 1968, 1578), there has been little improvement on the intrinsic activity of the catalyst. Attempt to develop new catalysis species have been hampered by the relatively harsh condition under which the reaction is conducted commercially (150-200 °C, 25-45 arm., in the presence of I") because under such conditions, virtually any source of rhodium will be converted to [Rh(CO)2l2]~ (D. Forster, J. Am. Chem. Soc., 1976, 98, 846) Reference may be made to U.S. Pat. No. 3,769,327 issued to F. E. Paulik et. al. wherein methanol is carbonylated with carbon monoxide gas at 175°C and 1000 psig pressure to acetic acid using the catalyst [Rh(CO)2l2]-. The process is similar to existing industrial condition for conducting the reaction. U.S. Pat. 4,990,654 issued to Wegman et.al. disclose production of acetate ester from alcohol using rhodium complex catalysts. The process comprises catalytic reaction of a mixture of methanol and ethanol and carbon monoxide in contact with a homogeneous catalyst of rhodium complex containing the ligands like Ph2P(CH2)nP(O)Ph2 (Ph = phenyl, n = 1-4) or Ph2P(CH2)nC(O)R or Ph2P(CH2)nCOOR (R=alkyl/aryl). The reaction was carried out at a temperature up to 130°C and reaction pressure up to about 250 psig. The main drawback of the process is that methanol conversion is only 70 %. Reference may be made to Wegman et.al. (J. Chem. Soc. Chem. Comm., 1987, 1891) wherein carbonylation in presence of catalyst [Rh(CO)2Cl(Ph2P(CH2)2P(O)Ph2)] was carried out at 80°C and 50 psig CO. The turnover frequency was 400 h-1. U.S.Pat. 5,488,153 issued to Baker et.al. discloses a process for the liquid phase carbonylation of methanol in presence of CO, a halogen promoter ( e.g. CH3I), water, rhodium complexes of Ph2PCH2P(S)Ph2 or 2-(diphenylphosphino)thiophenol. The reaction was performed in the temperature range of 25 - 250°C and at a pressure in the range 10 to 200 bar. The carbonylation rate was found to be considerably higher i.e. about 6 times higher than that in absence of the ligand in the system. The main drawback of the process is that it involves higher temperature and pressure. Baker et.al. (J.Chem.Soc.Chem.Soc., 1995, 197) also disclose that a catalyst cis- RhI(CO)Ph2PCH2P(S)Ph2 is about 8 times more active than the classic Monsanto catalyst [Rh(CO)2l2]~ for carbonylation of methanol at 185°C and at 70 bar pressure. In another disclosure, Dilworth et.al. (J. Chem. Soc. Chem. Comm., 1995, 1579) claimed that use of rhodium(I) complexes containing phosphinothiolate and thioether ligands resulted about 4 times higher rate in carbonylation of methanol to ethanoic acid than that of [Rh(CO)2l2]~. The reaction was carried out at 185°C and at 70 bar pressure. The draw back of the process is that it involves high temperature and pressure. Reference may be made to U.S Pat No. 5,973,197 issued to Denis et.al., wherein a method for preparing carboxylic acids by carbonylation of an alcohol in presence of rhodium complex catalyst. The carbonylation reaction was conducted at a temperature in the range 150 - 250°C and 1-100 bar pressures. Again the main drawback is the involvement of drastic reaction condition. The main object of the present invention is to provide a process for the preparation of novel rhodium metal complexes which obviates the drawback as detailed above. Another object of the present invention is to provide a process for preparing rhodium(I) complexes containing different types of ligands facilitating high electron density on the rhodium center and consequently can act as efficient catalyst precursors for carbonylation of methanol to acetic acid. Still another object of the present invention is to provide a process for preparing rhodium (I) complexes containing chelating ligands for providing higher stability of the complexes. Accordingly the present invention provides, a process for the preparation of novel rhodium metal complexes useful as catalyst for carbonylation of methanol to acetic acid and containing tertiary-phosphine chalcogenide selected from Ph3PO, Ph3PS and Ph3PSe or nitrogen donor ligands selected from amino phenol, benzoic acid or ambidentate ether phosphine ligand , said process comprises reacting a chlorobridged dimeric complex of rhodium [Rh(CO)2CI]2 in an organic solvent selected from CH2CI2, CHCI3, CH3COCH3 with two molar equivalent of the ligands as defined above under nitrogen atmosphere at room temperature for a period of 10 - 60 min, to get the desired rhodium metal complexes. In an embodiment of the present invention provides the preparation of novel rhodium (I) complex [Rh(CO)2CIL], where L is triphenyl phosphine chalcogenides Ph3PO or Ph3PS or Ph3PSe , by stirring a solution of chlorobridged dimeric complex [Rh(CO)2CI]2, in an organic solvent may be selected from CH2CI2, CHCI3, CH3COCH3 with two molar equivalent of Ph3PO or Ph3PS or Ph3PSe under nitrogen at room temperature for 10 -30 min. The IR spectra of the complexes show two equally intense terminal carbonyl absorption bands in the range 1950 - 2100 cm-1 attributable to cis disposition of the two carbonyl groups. The complexes [Rh(CO)2CIL] where L is Ph3PO or Ph3PS or Ph3PSe show 31P NMR resonance at 6 37.38, 46.71 and 32.21 respectively. In another embodiment of the present invention provides the preparation of novel rhodium(l) complex [Rh(CO)2CIL], where L is m-amino phenol or m-amino benzoic acid by reacting chlorobridged dimeric complex [Rh(CO)2CI]2 in an organic solvent like CH2CI2, CHCI3, CH3COCH3 etc. with two molar equivalent m-amino phenol or m-amino benzoic acid under nitrogen at room temperature for 10-30 min. The presence of two equally intense terminal v(CO) band in the range 1950-2100 cm-1, are consistent with cis disposition of the two carbonyl groups. Yet another embodiment of the present invention provides the preparation of rhodium(I) complexes [Rh(CO)2ClL], where L is ambidentate ether-phosphine ligand such as Ph2PCH2OCH3 or Ph2PCH2CH2OCH2CH3 by reacting chlorobridged dimeric complex [Rh(CO)2Cl]2 in an organic solvent like CH2C12, CHC13, CH3COCH3 etc. with two molar equivalent Ph2PCH2OCH3 or Ph2PCH2CH2OCH2CH3 under nitrogen at room temperature for 10 - 30 min. The complexes show two equally intense terminals v(CO) band in the range 1950 - 2100 cm"1, attributable to cis disposition of the two carbonyl groups. The 31PNMR spectra of of the [Rh(CO)2Cl(Ph2PCH2OCH3)] and [Rh(CO)2Cl(Ph2PCH2CH2OCH2CH3)] show doublet due to 103Rh-P coupling at 8 28.4 and 30.4 ppm respectively and the corresponding coupling constant values are 73.3 and 109.6 Hz. respectively. Still, another embodiment of the present invention provides the preparations of novel rhodium(I) cyclooctadiene complex [Rh(COD)ClL] where L is triphenyl phosphine chalcogenide (Ph3PO or Ph3PS or Ph3PSe) by refluxing a solution of chlorobridged dimeric complex [Rh(COD)Cl]2 in an organic solvent like CH2C12, CHC13) CH3COCH3 etc. with two molar equivalent of triphenyl phosphine chalcogenide ligands under nitrogen for 30 - 60 min. More than 30 years after the discovery, the Monsanto catalyst [Rh(CO)2I2]- is still preferred as commercial catalyst for carbonylation of methanol to acetic acid. Any metal complexes to act as efficient catalyst should possess high electron density on the metal centre. In the present invention, the high electron density on the metal in the complexes [Rh(CO)2ClL], where L is triphenylphosphine chalcogenide (PPh3O, PPh3S and PPh3Se) is due to strong interaction between 'Soft' rhodium(I) with 'Soft sulfur' and more 'Softer selenium' donors; where as in case of phosphine oxide complex the high electron density on the metal is due to higher elcetron density donation from the 'Hard oxygen' to the metal because of no back donation due to absence of dπ back bonding. In the present invention, the complexes [Rh(CO)2ClL], where L is a nitrogen donor ligand like amino phenol / amino benzoic acid or ambidentate ether-phosphine ligand becomes electron rich because both nitrogen and phosphorous atom are strong electron donor. Moreover, the nitrogen donor and ether-phosphine ligands also contain another donor such as -OH or -COOH or -OR (R = Me, Et), which may take part in chelate bond formation as and when required in the catalytic system and thus enhancing stabilization of the catalyst. Such chelate metal complexes may open the weaker Rh-O bond reversibly for substrate coordination during the course of the catalytic reaction and hence facilitating the reaction. The higher catalytic activity of the complexes [Rh(COD)ClL] (L = PPh3O or PPh3S or PPh3Se) over [Rh(CO)2l2]- is expected due to higher nucleophilicity of the rhodium center caused by COD molecule which is lesser π-acceptor as compared to CO molecule and stronger phosphine chalcogenide donor compared to iodine atom. Moreover, such complexes get higher stability due to COD chelation which is beneficial for the catalytic reaction. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. EXAMPLE - 1 To a solution of of [Rh(CO)2Cl]2 (0.1 g, 0.25 mmol) in CHC13 (10 ml) PPh3O (0.14 g, 0.5 mmol) was added. The reaction mixture was stirred for 10 minutes at room temperature under nitrogen during which the colour of the solution changes from reddish yellow to deep brown. The resulting solution was dried in vacuum and the solid compound obtained was washed with petroleum ether and kept over silica gel in a desiccator. Yield : 99 % . Anal. Calc. for C20H15ClO3PRh : C, 50.8 %; H, 3.2 %. Found : C, 51.3 %; H, 3.1 %. IR (KBr / cm-1) : 2005 , 2080 v(CO); 1 160 v(PO). 1H NMR (CDC13 / δ in ppm): 7.49 - 7.74 (m, 15H, C6H5). 31P NMR (CDC13 / 8 in ppm): 37.38. I3C NMR (CDC13 / 5 in ppm): 132.43 - 128.63 (m, ISC,C6H5), 181 (s, 2C, CO). EXAMPLE - 2 To a solution of of [Rh(CO),C1]2 (0.1 g, 0.25 mmol) in CHC13 (10 ml) PPh3S (0.15 g, 0.5 mmol) was added. The reaction mixture was stirred for 10 minutes at room temperature during which the colour of the solution changes from reddish yellow to reddish brown. The resulting solution was dried in vacuum and the solid compound obtained was washed with petroleum ether and kept in a desiccator. Yield : 98 % . Anal. Calc. for C20H15ClO2SPRh : C, 49.2 %; H, 3.1 %. Found : C, 51.5 %; H, 3.7 %. IR (KBr / cm-1) : 2001 , 2068 v(CO); 593 v(PS). 1H NMR (CDC13 / δ in ppm): 7.50 - 7.84 (m, 15H, C6H5). 31P NMR (CDC13 / 8 in ppm): 46.71. 13C NMR (CDC13 / 8 in ppm): 133.15 -129.15 (m, 18C,C6H5), 180 (s, 2C, CO). EXAMPLE-3 To a solution of of [Rh(CO)2Cl]2 (0.1 g, 0.25 mmol) in CHC13 (10 ml), PPh3Se (0.17 g, 0. 5 mmol) was added. The reaction mixture was stirred for 10 minutes at room temperature during which the colour of the solution changes from reddish yellow to dark red. The resulting solution was dried in vacuum and the solid compound obtained was washed with petroleum ether and kept in a desiccator. Yield : 99 % . Anal. Calc. for C2oH15C102SePRh : C, 44.9 %; H, 2.8 %. Found : C, 44.5 %; H, 3.3 %. IR (KBr / cm-1): 1985 , 2058 v(CO); 538 v(PSe). 1H NMR (CDC13 / 6 in ppm): 7.26 - 7.76 (m, 15H, C6H5). 31P NMR (CDC13 / δ in ppm): 32.21.13C NMR (CDC13 / 6 in ppm): 134.64 -128.74 (m, 18C,C6H5), 183 (s, 2C, CO). EXAMPLE-4 [RhCO)2Cl]2 (0.020 g; 0.05 mmol) in 15 ml acetone was treated with m-aminophenol (0.0112 g; 0.10 mmol) and stirred for about 30 minutes at room temperature under nitrogen. The solvent was then evaporated under reduced pressure to produce a violet coloured compound which was washed with minimum quantity of the solvent followed by drying over fused CaC12h in a dessicator. Yield : 99 % . Anal. Calc. for C8H7ClO3NRh : C, 31.63 %; H, 2.3 %. Found : C31.9 %; H, 2.4 %. IR (KBr / cm-1) : 2092, 2000 v(CO). EXAMPLE -5 [RhCO)2Cl]2 (0.020 g; 0.05 mmol) in 15 ml acetone was treated with m-aminobenzoic acid (0.0141 g; 0.10 mmol) and stirred for about 30 minutes at room temperature under nitrogen. The solvent was then evaporated under reduced pressure to produce a violet coloured compound which was washed with minimum quantity of the solvent followed by drying over fused CaCl2 in a dessicator. Yield : 98 % . Anal. Calc. for C9H7ClO4NRh : C, 32.57 %; H, 2.11 %. Found : C 32.7 %; H, 2.1 %. IR (KBr / cm-1) :2092,2010v(CO). EXAMPLE -6 To a solution of [Rh(CO)2Cl]2 (0.02 g, 0.05 mmol) in CH2C12 (10 ml) Ph2PCH2OCH3 (0.025 g, 0.11 mmol) was added. The reaction mixture was stirred under nitrogen at room temperature for 30 min. during which the colour of the solution changes from reddish yellow to reddish brown. The solvent was then removed under vacuum to give a reddish brown solid. The product was was washed thoroughly with hexane - petroleum ether mixture. Yield : 95 % . Anal. Calc. for C16H15ClO3PRh : C, 45.28 %; H, 3.53 %. Found : C, 45.41 %; H, 3.40 %. IR (KBr / cm-1) : 1985 , 2060 v(CO); 1110 v(COC). 1H NMR (CDC13 / 6 in ppm): 7.3 - 7.8 (m, 10H, C6H5), 3.8 (d, PCH2, JHH= 11.15 Hz), 3.2 (s, OCH3). 31P NMR (CDC13 / δ in ppm): 28.4 (d, JRh-p = 73.3 Hz).13C NMR (CDC13 / δ in ppm): 132.2 - 128.5 (m, 10C, C6H5), 187.5 (s, 2C, CO). EXAMPLE-7 To a solution of [Rh(CO)2Cl]2 ( 0.02g, 0.05 mmol) in CH2C12 (10 ml) Ph2PCH2CH2OCH2CH3 (0.028 g, 0.11 mmol) was added. The reaction mixture was stirred under nitrogen at room temperature for 30 min. during which the colour of the solution changes from reddish yellow to reddish brown. The solvent was then removed under vacuum to give a reddish brown solid. The product was was washed thoroughly with hexane - petroleum ether mixture. Yield : 90 % . Anal. Calc. for C18H19ClO3PRh : C, 47.78 %; H, 4.20 %. Found : C, 48.01 %; H, 4.23 %. IR (KBr / cm-1) : 2000 , 2065 v(CO); 1113 v(COC). 'H NMR (CDC13 / δ in ppm): 7.3 - 7.7 (m, 10H, C6H5), 2.7 (dt, PCH2, JHH= 7.45 Hz), 3.9 (t, PCH2CH2, JHH= 4.91 Hz), 3.5 (q, OCH2CH3, JHH= 5.80 Hz) 1.8 (t, CH3, JHH= 2.07 Hz). 3IP NMR (CDC13 / δ0 in ppm): 30.4 (d, JRh-P = 109.6 Hz).13C NMR (CDC13 / δ in ppm): 131.9 - 128.8 (m, 10C, C6H5), 188.2 (s, 2C, CO). EXAMPLE -8 [Rh(COD)Cl]2 (O.lg, 0.203) was dissolved in CHC13 (40 cm3) and to this solution, PPh3O ( 0.12 g, 0.406 mmol) was added. The reaction mixture was refluxed for 0.5 h"1 under nitrogen . The colour of the solution changes from yellow to orange-yellow. The solution was then evaporated to dryness. The solid compound thus obtained was washed with petroleum ether and stored over silica gel in a desicator. Yield : 98 % . Anal. Calc. For C26H27ClPORh in %: C 59.54; H, 5.15; Found: C, 59.24; H, 5.03. 1H NMR (CDC13 / δ in ppm): 7.70 - 7.27 (m, C6H5), 4.22 (-CH=CH), 2.49 (-CH2-C). 13C{1H} NMR (CDC13 / δ in ppm): 133.13 -128.40 (m, C6H5), 78.76 (-CH=CH), 30.11 (-CH2-C). 31P{1H} NMR (CDC13 / δ in ppm): 29.81. IR (KBr / cm-1): 1170 (v PO). EXAMPLE - 9 [Rh(COD)Cl]2 (0.1 g, 0.203 mmol) was dissolved in CHC13 (40 cm3) and to this solution, PPh3S ( 0.12 g, 0.406 mmol) was added. The reaction mixture was refluxed for 0.5 h-1 under nitrogen . The colour of the solution changes from yellow to orange. The solution was then evaporated to dryness. The solid compound thus obtained was washed with petroleum ether and stored over silica gel in a desicator. Yield : 99 %. Anal. Calc. For C26H27ClPSRh in %: C, 57.77; H, 5.00; Found: C, 58.01; H, 5.07. 1H NMR (CDC13 / δ in ppm): 7.75 -7.41 (m, C6H5), 5.30 (-CH=CH), 2.48 (-CH2-C). 13C{1H} NMR (CDC13 / δ in ppm): 132.44 -128.41 (m, C6H5), 78.57 (-CH=CH), 30.85 (-CH2-C). 31P{1H} NMR (CDC13 / 5 in ppm): 43.87. IR (KBr / cm-1): 600 (v PS). EXAMPLE -10 [Rh(COD)Cl]2 (0.1 g, 0.203 mmol) was dissolved in CHC13 (40 cm3) and to this solution, PPh3Se (0.14 g, 0.406 mmol) was added. The reaction mixture was refluxed for 0.5 h-1 under nitrogen . The colour of the solution changes from yellow to brown. The solution was then evaporated to dryness. The solid compound thus obtained was washed with petroleum ether and stored over silica gel in a desicator. Yield : 99 %. Anal. Calc. For C26H27ClPSeRh in %: C, 53.15; H, 4.59; Found: C, 53.49; H, 4.79.1H NMR (CDC13 / δ in ppm): 7.76 -7.26 (m, C6H5), 4.23 (-CH=CH), 2.46 (-CH2-C). 13C{1H} NMR (CDC13 / δ in ppm): 134.87 - 128.66 (m, C6H5), 78.79 (-CH=CH), 33.10 (-CH2-C). 31P{1H} NMR (CDC13 / δ in ppm): 31.81(d, JPse = 364 Hz). IR (KBr / cm-1): 540 (v PSe). In summary, the metal complex [Rh(CO)2ClL] or [Rh(COD)ClL] (L is triphenyl phosphine chalcogenide or ether phosphine or nitrogen donor ligand such as amino phenol or amino benzoic acid) is prepared by reacting bridge splitting reaction of chlorobridged dimeric complexes [Rh(CO)2Cl]2 or [Rh(COD)Cl]2 with the appropriate ligand. Due to the presence of different types of donors atom such as oxygen, nitrogen, phosphorous, sulfur and selenium in the ligands the metal atom become electron rich and thus may behave as a good carbonylation catalyst. The main advantages of the present invention are : (i) The complexes are very much air stable. (ii) The complexes are very much susceptible to oxidative addition reaction (iii) The complexes containing the chelate forming ligands are very stable in chelated form in solution. (iv) The complexes can be used as catalyst precursors for carbonylation of methanol to acetic acid and ester. We Claim: 1. A process for the preparation of novel rhodium metal complexes useful as catalyst for carbonylation of methanol to acetic acid and containing tertiary-phosphine chalcogenide selected from Ph3PO, Ph3PS and Ph3PSe or nitrogen donor ligands selected from amino phenol, benzole acid or ambidentate ether phosphine ligand , said process comprises reacting a chlorobridged dimeric complex of rhodium [Rh(CO)2CI]2 in an organic solvent selected from CH2CI2, CHCI3, CH3COCH3 , with two molar equivalent of the ligands as defined above under nitrogen atmosphere at room temperature for a period of 10 - 60 min, to get the desired rhodium metal complexes. 2. A process for the preparation of novel rhodium metal complexes useful as catalyst for carbonylation of methanol to acetic acid substantially as herein described with reference to the examples.

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