Oxidative addition reaction of rhodium(I) carbonyl complexes of the pyridine-aldehyde ligands and their catalytic activity in carbonylation reaction

Abstract

Rhodium(I) carbonyl complexes [Rh(CO) 2 ClL] ( 1 ) where L = Py-2-CHO ( a ), Py-3-CHO ( b ) and Py-4-CHO ( c ) have been synthesized and characterized by elemental analyses, IR, 1 H and 13 C NMR spectroscopy. The complexes 1 undergo oxidative addition reactions with different types of electrophiles such as CH 3 I, C 2 H 5 I, C 6 H 5 CH 2 Cl and I 2 to yield [Rh(CO)(COCH 3 )ClIL] ( 2 ), [Rh(CO)(COC 2 H 5 )ClIL] ( 3 ), [Rh(CO)(COCH 2 C 6 H 5 )Cl 2 L] ( 4 ) and [Rh(CO)ClI 2 L] ( 5 ) complexes, respectively. The kinetic study of the complexes 1 with CH 3 I reveals a two-stage kinetics and the second-stage reactions are faster than that of the first stage by about 80–100 times. The rate of reaction of 1a is higher than that of 1b and 1c . The catalytic activity of complexes 1 in carbonylation of methanol, in general, is higher (TON 800 – 1250) than that of the well-known species [Rh(CO) 2 I 2 ] − (TON 650). Rhodium(I) carbonyl complexes [Rh(CO) 2 ClL] (L = Py-2-CHO, Py-3-CHO and Py-4-CHO) have been synthesized and their oxidative reactivity towards different electrophiles like CH 3 I, C 2 H 5 I, C 6 H 5 CH 2 Cl and I 2 were studied. The catalytic activity of the complexes in carbonylation of methanol, in general, is higher than that of the well-known species [Rh(CO) 2 I 2 ] − .