Rhodium carbonyl complexes containing pyridine carboxylic acid ligands: Reactivity towards various electrophiles and catalytic activity

The complex [Rh(CO)(2)Cl](2) reacts with two molar equivalent of pyridine carboxylic acids ligands Py-2-COOH(a), Py-3-COOH(b) and Py-4-COOH(c) to yield rhodium(I) dicarbonyl chelate complex [Rh(CO)(2)(L')](1a) {L' = eta(2)-(N,O) coordinated Py-2-COO-(a')} and non-chelate complexes [Rh(CO)(2)CIL''](1b,c) (L'' = eta(1)-(N) coordinated Py-3-COOH(b), Py-4-COOH(c)). The complexes 1 undergo oxidative addition (OA) reactions with different electrophiles such as CH3I, C2H5I, C6H5CH2Cl and I-2 to give penta coordinated Rh(III) complexes of the types [Rh(CO)(CORn)XL'], {n=1,2,3; R-1 =-CH3(2a); R-2 =-C2H5(3a); X=I and R-3 =-CH2C6H5 (4a); X=Cl}, [Rh(CO)I2L'](5a), [Rh(CO)(CORn)ClXL''] {R-1=-CH3(6b,c); R-2 =-C2H5(7b,c); X=I and R-3=-CH2C6H5 (8b,c); X=Cl} and [Rh(CO)ClI2L''](9b,c). The complexes have been characterized by elemental analysis, IR and H-1 NMR spectroscopy. Kinetic data for the reaction of 1a-b with CH3I indicate a first order reaction. The catalytic activity of 1a-c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 810-1094) is obtained compared with that of the well-known commercial species [Rh(CO)(2)I-2](-) (TON = 653) at mild reaction conditions (temperature 130 +/- 5 degrees C, pressure 35 +/- 5 bar). (C) 2008 Elsevier B.V. All rights reserved.