Carbonylrhodium complexes of pyridine ligands and their catalytic activity towards carbonylation of methanol

The cis‐Rh(CO)₂ClL] (1) complexes, where L = 2‐methylpyridine (a), 3‐methylpyridine (b), 4‐methylpyridine (c), 2‐phenylpyridine (d), 3‐phenylpyridine (e), 4‐phenylpyridine (f), undergo oxidative addition reactions with various electrophiles, like CH₃I, C₂H₅I, C₆H₅CH₂Cl or I₂, to yield complexes of the types Rh(CO)(COR)ClXL] (2) (where R = CH₃ (i), C₂H₅ (ii), X = I; R = C₆H₅CH₂ (iii), X = Cl) or Rh(CO)ClI₂L] (3) and Rh(CO)₂ClI₂L] (4). The pseudo‐first‐order rate constants of CH₃I addition with complexes 1 containing pyridine (g) and 2‐substituted pyridine (a and d) ligands were found to follow the order pyridine >2‐methylpyridine >2‐phenylpyridine. The catalytic activity of complexes 1 containing different pyridine ligands (a–g) on carbonylation of methanol was studied and, in general, a higher turnover number was obtained compared with that of the well‐known species Rh(CO)₂I₂]^?. Copyright © 2002 John Wiley & Sons, Ltd.