Chelate and trans effect of P,O donor phosphine ligands on rhodium catalyzed carbonylation of methanol

Four complexes of the type [Rh(CO)Cl(eta(2)-P,O-L)](1a,1b) and [Rh(CO)Cl(eta(1)-P-L)(2)](2a,2b), where L = Ph2PC6H4-2-OCH3(a) and Ph2PC6H4-2-CH2OCH3(b), have been synthesized by the reaction of [Rh(CO)(2)Cl](2) with appropriate mol equivalents of the ligands in CH2Cl2. The complexes show single intense v(CO) bands in the range 1965-1989 cm(-1) indicating the presence of terminal carbonyl groups. All the complexes have been characterized by elemental analyses, mass spectrometry. IR and multinuclear NMR (H-1, P-31 and C-13) spectroscopy, and the molecular structure of the ligand b is determined by single crystal X-ray diffraction. The complexes undergo oxidative addition (OA) with excess CH3I to afford Rh(III)-acyl complexes of the type [RhCl(COCH3)I(L)](3a,3b) and [RhCl(COCH3)I(L)(2)](4a,4b). The kinetic data for the OA reactions with CH3I indicate a first order reaction and also exhibit that the rate of OA for the chelate complexes (1a and 1b) is higher than those of trans-complexes (2a and 2b). The catalytic efficiencies of 1a, 1b, 2a and 2b in carbonylation of methanol exhibit higher Turn Over Frequency (TOF) 689-1808 h(-1) than the well-known Monsanto's species [Rh(CO)(2)I-2](-)(TOF = 464-1000 h(-1)) under similar experimental conditions. The catalytic activities vary in the order as 1a > 1b > 2a > 2b. (C) 2011 Elsevier B.V. All rights reserved.