Title of Invention

NOVEL RHODIUM CARBONYL BASED LIGAND CATALYST AND A PROCESS FOR THE PREPARATION THEREOF

Abstract

Novel rhodium carbonvl based ligand catalyst and process for the preparation thereof The present invention provides a novel Rhodium (I) carbonyl complexes of the type [Rh(CO)2L/] (!_" = rf-(U,O) coordinated Py-2-COO") and [Rh(CO)2CIL//] (!_" = = //-(N) coordinated Py-3-COOH, Py-4-COOH) useful as catalyst precursor. This invention further provides a process for the preparation of [Rh(CO)2CI(Py-3-COOH)], [Rh(CO)2(Py-2-COO-)] and [Rh(CO)2CI(Py-4-COOH)]. The efficacy trend of the these complexes as a catalyst precursor for carbonylation of alcohols to acids or esters is in the order of [Rh(CO)2CI(Py-3-COOH)] > [Rh(CO)2(Py-2-COO")] > [Rh(CO)2CI(Py-4-COOH)].

Full Text

FIELD OF THE INVENTION The present invention relates to a novel rhodium carbonyl based ligand catalyst. It also relates to a process for the preparation of novel rhodium(l) carbonyl complexes containing singly charged bidentate nitrogen-oxygen donors ligands useful as carbonylation catalysts. BACKGROUND OF THE INVENTION The present invention provides a process preparation of new rhodium(l) carbonyl complexes of ligands containing aromatic hetero backbone. The rhodium carbonyl complexes prepared by the present invention are useful as catalyst precursors for carbonylation of alcohol to carboxylic acid and ester. Reference may be made to the workDenise et. al. (J. Organomet. Chem, 63, 1973, 423) wherein a few pyridine or substituted pyridine complexes of rhodium metal of the type [Rh(COD)CIL] (COD = 1,5-cyclooctadiene; L = pyridine, 2-vinyl pyridine, 2-methyl pyridine, 4-methyl pyridine) have reported. The drawback of the work is that it did not disclose any catalytic activities of the complexes. Reference may be made to the work of Lawson & Wilkinson (J. Chem. Soc. A, 1965, 1900) wherein they disclosed the preparation of few rhodium(l) carbonyl complexes of pyridine or chloro pyridine. The drawback of the work is that it did not disclose any catalytic activities of the complexes. Reference may be made to the work of Ugo et. al. (J. Organomet. Chem, 11, 1968,159) wherein a few nitrogen-oxygen donors complexes of rhodium metal of the type (CO)2Rh(Chel); Chel = 8-oxyquinolate, quinaldinate, a-pyridinecarboxylate, salicylaldoximate) have been reported. The drawbacks are that they did not report any non chelating carbonyl complexes and also there was no disclosure of any catalytic application. Reference may be made to the work of Chen et.al. (Trans. Met. Chem., 19, 1994, 418) wherein they have reported dicarbonyl complexes of the type [Rh(CO)2(LL/)] where LL' = salicylaldoximate, 8-oxyquinolinate, glycinate, leucinate, aminophenolate or pyridine carboxylate and their catalytic activity towards hydroformylation of styrene at atmospheric pressure of CO : H2 (1:1). The drawback is that they did not disclose the carbonylation catalysis. Reference may be made to the work of Sivasubramanian et. al. (Trans. Met. Chem., 1982, 7, 346) wherein they reported the first metal-nitrone complex (i.e.metal complexes of nitrogen-oxygen donors ligands) where metals are used from the 1st row transition metal series. Other few reports of metal nitrone complex appeared in literature e.g. Frederick et. al. (Inorg. Chem. 37, 1998, 1446, J. Chem. Soc., Da/ton Trans., 1998, 4055) and Thirumalaikumar et. al. (Indian J. Chem, 38A, 1999, 720). No catalytic evaluation was reported. Since the first report of catalysis by [Rh(CO)2l2]" (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 atm., 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. 3,769,329 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(as above) for conducting the reaction and therefore the same drawback persists. Reference may be made to U.S. Pat. 4,990,654 issued to Wegman et. al. wherein they disclosed 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(0)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 the work of Wegman et.al. (J. Chem. Soc. Chem. Comm., 1987, 1891) wherein carbonylation in presence of catalyst [Rh(CO)2CI(Ph2P(CH2)2P(O)Ph2)] was carried out at 80°C and 50 psig CO. The turnover frequency was 400 h"1. The drawbacks are that they did not report the percentage of methanol conversion and the selectivity. Reference may be made to U.S.Pat. 5,488,153 issued to Baker et.al. wherein they claimed 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 drawback of the process is that it involves higher temperature and pressure. Reference may be made to the work of Cavell et. al (US Pat. 5352813) wherein an improved process for the carbonylation of methanol to acetic acid and or its ester using a catalyst precursor composed of transition metal complex containing a hetero functional bidentate phosphorous-nitrogen donors ligand under CO pressure of 40 psi. and at 80 °C have been disclosed. The drawback is that the patent did not claim any yield of the catalytic reaction process. Reference may be made to the work of Baker et.al. (J. Chem. Soc. Chem. Soc., 1995, 197) wherein disclosed the catalytic activity of a catalyst c/'s-Rhl(CO)Ph2PCH2P(S)Ph2 which 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. The draw back of the process is that it required high temperature and pressure. Reference may be made to the work of Dilworth et.al. (J. Chem. Soc. Chem. Comm., 1995, 1579) wherein they claimed that use of rhodium(l) 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 have been disclosed. 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. Since the discovery, Monsanto catalyst [RlXCOhh]" is still preferred as commercial catalyst for carbonylation of methanol to acetic acid. It is well known that a complex to act as an efficient catalyst, it should possess high electron density on the metal center which can be achieved by introducing different types of electron donor ligands in the metal complex species. It is anticipated that a 'Hard' donors like nitrogen and oxygen atom would increase the electron density on the central rhodium atom causing the complexes to behave as an efficient catalyst. OBJECTS OF THE INVENTION The main object of the present invention is to provide novel rhodium carbonyl complexes of nitrogen-oxygen donors based ligands useful as carbonylation catalysts. Another object of the present invention is to provide a process for preparing rhodium(l) complexes containing electron rich ligand oxygen and Nitrogen donor atoms, as efficient catalyst precursors for carbonylation of alcohol to acid and/or ester. SUMMARY OF THE INVENTION Accordingly, the present invention provides a Rhodium carbonyl based complex of general formula [Rh(Co)2XL] wherein X is optional and is Cl, L is a nitrogen-oxygen containing bidentate ligand selected from Pyridine- 2-COO", Pyridine -3-COOH and Pyridine-4-COOH. In an embodiment of the present invention the Rhodium carbonyl based complex is represented by a group of the following compounds: [Rh(CO)2(Py-2-COO-)]=1, [Rh(CO)2CI(Py-3-COOH)]=2, and [Rh(CO)2CI(Py-4-COOH)]=3. In yet another embodiment these complexes are as catalyst precursor for the carbonylation of alcohols to acids or esters. The present invention further provides a process for the preparation of Rhodium carbonyl based complex, which comprises reacting [Rh(Co)2CI]2 with nitrogen-oxygen containing bidentate ligand in an organic solvent, under nitrogen atmosphere, under stirring, at a temperature of about 25°C, for a period of about 10 minutes to 1 hour, followed by the evaporation of solvent and washing the resultant mass with petroleum ether to obtain the desired product. In yet another embodiment the nitrogen-oxygen containing bidentate ligand used is selected from Py-2-COO"; Py-3-COOH and Py-4-COOH. A process as claimed in claim 4, wherein the molar ratio of [Rh(Co)2CI]2 to nitrogen-oxygen containing bidentate ligand used is in the range of 1:1.5 to 1:2. In yet another embodiment the organic solvent used is selected from the group consisting of dichloromethane, chloroform, methanol, acetone and any combination thereof. In yet another embodiment the Rhodium carbonyl based catalyst [Rh(Co)2XL] obtained is represented by a group of the following compounds [Rh(CO)2(Py-2-COCr)]; [Rh(CO)2CI(Py-3-COOH)] and [Rh(CO)2CI(Py-4-COOH)]. In still another embodiment the Rhodium carbonyl based catalyst is useful as a catalyst precursor for carbonylation of alcohols to acids or esters. DETAILED DESCRIPTIO OF THE INVENTION The present invention provides a process for the preparation of novel rhodium carbonyl complexes of nitrogen-oxygen donors based ligands useful as carbonylation catalysts which comprises preparation of rhodium(l) carbonyl complexes containing chloride and nitrogen-oxygen based donors ligands such as acid substituted pyridines by reacting chlorobridged dimeric complex [Rh(CO)2CI]2 in an organic solvent like CH2Cl2, CHCI3 etc. with two molar equivalent (Rh : Ligand = 1:2 mol ratios) of the respective ligand in organic solvent like CH2CI2, CHCI3 etc. or a warm mixture of CH3OH, CH3COCH3l CH2CI2 etc. under nitrogen atmosphere at room temperature for a period of about 10 minutes to 1 hour under stirring condition and such newly synthesized electron rich rhodium metal complexes exhibit efficient catalytic applications in carbonylation processes comprising contacting the catalyst, carbon monoxide with liquid reaction composition of methanol, a halogen promoter preferably methyl iodide, water at a temperature in the range 130 ± 5 °C and at a pressure of 35 ± 5 bar for a period of 1 hour with high conversion and high selectivity. It discloses the preparation of new and novel rhodium(l) carbonyl complexes containing singly charged bidentate nitrogen-oxygen donors ligands containing hetero backbone and the catalyst precursors (rhodium(l) carbonyl complexes containing bidentate nitrogen-oxygen donors ligands), carbon monoxide with liquid reaction composition of methanol, a halogen promoter preferably methyl iodide, water at a temperature in the range 130 ± 5 °C and at a pressure of 35 ± 5 bar for a period of 1 hour with high conversion and high selectivity.lt also discloses the oxidative addition reactions of the coordinatively unsaturated rhodium(l) carbonyl complexes containing bidentate nitrogen-oxygen donors ligands with electrophile CH3I, which is the key step in carbonylation of alcohol. And provide a catalyst containing electron rich ligand 'Hard1 and 'Hard' donors atoms, (unequal hardness) facilitating high electron density on the rhodium center and higher stability of the complexes through possible chelate formation, and thus causing facile oxidative addition reactions with different electrophiles and consequently can act as efficient catalyst precursors for carbonylation of alcohol to acid and/or ester. The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of the present invention. EXAMPLE-1 To a solution of [Rh(CO)2CI]2 (20 mg, 0.051 mmol) in CH2CI2 (5 ml) Pyridine-2-carboxylic acid (12.66 mg, 0.103 mmol) in CH2CI2 (3 ml) was added with constant stirring to yield [Rh(CO)2(Py-2-COO")]. The solution was stirred for 1 hour. Violet coloured compound was separated out. The solvent was evaporated out under vacuum and the violet mass obtained was washed with petroleum ether for several times. Yield :88%. Anal. Calc. for C8H4NO4Rh: C, 34.16 %; H, 1.42 %; N, 4.98%; Found : C, 34.13 %; H, 1.37; N, 4.96 %. EXAMPLE- 2 To a solution of [Rh(CO)2CI]2 (20 mg, 0.051 mmol) in CH2CI2 (10 ml) Pyridine-3-carboxylic acid (12.66 mg, 0.103 mmol) in a warm mixture of CH2CI2, CH3OH and ChhCOCHa (7 ml) was added with constant stirring to yield [Rh(CO)2CI(Py-3-COOH)]. The solution was stirred for 10 minutes. Brick-red coloured compound was separated out. The solvent was evaporated out under vacuum and the brick-red mass obtained was washed with dry petroleum ether for several times. Yield : 96%. Anal. Calc. for C8H5CINO4Rh: C, 30.23 %; H, 1.57 %; N, 4.41%; Found : C, 30.26 %; H, 1.60; N, 4.39 %. EXAMPLE - 3 To a solution of [Rh(CO)2CI]2 (20 mg, 0.051 mmol) in CH2CI2 (10 ml) Pyridine-4-carboxylic acid (12.66 mg, 0.103 mmol) in a warm mixture of CH2CI2, CH3OH and CH3COCH3 (7 ml) was added with constant stirring to yield [Rh(CO)2CI(Py-4-COOH)]. The solution was stirred for 30 minutes. Brick-red coloured compound was separated out. The solvent was evaporated out under vacuum and the brick-red mass obtained was washed with dry petroleum ether for several times. Yield : 96%. Anal. Calc. for C8H5CINO4Rh: C, 30.23 %; H, 1.57 %; N, 4.41%; Found : C, 30.21 %; H, 1.62; N, 4.37 %. EXAMPLE - 4 0.099 mol of MeOH, 0.016 mol of CH3I, 0.060 mol of H2O, 0.058 mmol of [Rh(CO)2(Py-2-COO")] catalyst precursors were charged into a previously degassed 100 cm3 reactor (Berghof, Germany) equipped with a magnetic stirrer and then pressurized with CO gas (20 bar at room temperature, 0.080 mol). The temperature of the reaction was increased to 130 ± 5 °C [pressure 35 ± 2 bar], and the reaction was continued for 1 hour. After catalytic reaction, the products were collected and analyzed. The product was a mixture (total conversion 48% wt./wt.) of acetic acid (6.2 % wt./wt.) and methyl acetate (41.8 % wt./wt.) and the Turn Over Number (TON) was 923. Conversion = {[CO consumed (mol)]/[CO charged (mol)]}. CO consumption was determined from analysis of products by GC. Yields of methyl acetate and acetic acid were obtained from GC analysis. TON = [Amount of product (mol)]/[Amount of catalyst (Rh mol)]. EXAMPLE - 5 0.099 mol of MeOH, 0.016 mol of CH3I, 0.060 mol of H2O, 0.051 mmol of [Rh(CO)2CI(Py-3-COOH)] catalyst precursors were charged into a previously degassed 100 cm3 reactor (Berghof, Germany) equipped with a magnetic stirrer and then pressurized with CO gas (20 bar at room temperature, 0.080 mol). The temperature of the reaction was increased to 130 ± 5 °C [pressure 35 ± 2 bar], and the reaction was continued for 1 hour. After catalytic reaction, the products were collected and analyzed. The product was a mixture (total conversion 57% wt./wt.) of acetic acid (9.5% wt./wt.) and methyl acetate (47.5 % wt./wt.) and the Turn Over Number (TON) was 1094. EXAMPLE - 6 0.099 mol of MeOH, 0.016 mol of CH3I, 0.060 mol of H2O, 0.051 mmol of [Rh(CO)2CI(Py-4-COOH)] catalyst precursors were charged into a previously degassed 100 cm3 reactor (Berghof, Germany) equipped with a magnetic stirrer and then pressurized with CO gas (20 bar at room temperature, 0.080 mol). The temperature of the reaction was increased to 130 ± 5 °C [pressure 35 ± 2 bar], and the reaction was continued for 1 hour. After catalytic reaction, the products were collected and analyzed. The product was a mixture (total conversion 42.1% wt./wt.) of acetic acid 6.55 % wt./wt.) and methyl acetate (35.55 % wt./wt.) and the Turn Over Number (TON) was 810. In summary, rhodium metal complexes [Rh(CO)2L/] and [Rh(CO)2CIL//] where !_' = Py-2-COO"; L" = Py-3-COOH, Py-4-COOH are prepared by bridge splitting reaction of chlorobridged dimeric complexes [Rh(CO)2CI]2 with the ligands L1 and L;/ in 1 : 2 mol ratio at room temperature. ADAVNTAGES OF THE INVENTION > The ligands are singly charged bidentate nitrogen-oxygen donors and capable of forming stable chelate complex which is highly required for catalytic reaction steps. > The metal center in the complexes will be electron rich because of presence of 'Hard' donors and therefore expected to exhibit high nucleophilicity required for high catalytic activity. > The complexes in general are stable in air as well as in solution. > The complexes are coordinatively unsaturated and can easily undergo oxidative addition reaction with different electrophiles like alkyl halide, which is the key step in catalytic carbonylation of alcohol. > The complexes can be used as catalyst precursors for carbonylation of alcohol. We claim: 1. A Rhodium carbonyl based complex of general formula (Formula Removed) wherein X is optional and is CI L is a nitrogen-oxygen containing bidentate ligand selected from Pyridine- 2-COO", Pyridine -3-COOH and Pyridine-4-COOH. 2. A Rhodium carbonyl based complex as claimed in claim 1, is represented by a group of the following compounds: [Rh(CO)2(Py-2-COO-)]=1, [Rh(CO)2CI(Py-3-COOH)]=2, and [Rh(CO)2CI(Py-4-COOH)]=3. 3. A Rhodium carbonyl based complex as claimed in claim 1, is useful as a catalyst precursor for the carbonylation of alcohols to acids or esters. 4. A process for the preparation of Rhodium carbonyl based complex as claimed in claim 1, which comprises; reacting [Rh(CO)2CI]2 with nitrogen-oxygen containing bidentate ligand in an organic solvent, under nitrogen atmosphere, under stirring, at a temperature of 25°C, for a period of 10 minutes to 1 hour, followed by the evaporation of solvent and washing the resultant mass with petroleum ether to obtain the desired product. 5. A process as claimed in claim 4, wherein the nitrogen-oxygen containing bidentate ligand is selected from Py-2-COO'; Py-3-COOH and Py-4-COOH. 6. A process as claimed in claim 4, wherein the molar ratio of [Rh(CO)2CI]2 to nitrogen-oxygen containing bidentate ligand is in the range of 1:1.5 to 1:2. 7. A process as claimed in claim 4, wherein the organic solvent is selected from the group consisting of dichloromethane, chloroform, methanol, acetone and any combination thereof. 8. A process as claimed in claim 4, wherein the Rhodium carbonyl based catalyst is useful as a catalyst precursor for carbonylation of alcohols to acids or esters.

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2469-del-2006-abstract.pdf

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2469-del-2006-Correspondence Others-(28-05-2012).pdf

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2469-del-2006-form-3.pdf

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