EQUILIBRIA AND RATES OF OLEFIN SUBSTITUTION IN ZEROVALENT PALLADIUM COMPLEXES CONTAINING A 2-PYRIDYLMETHANIMINE LIGAND

Equilibrium constants K-c have been determined for the olefin susbtitu tion in palladium(0) alpha-diimine olefin (ol) complexes [Pd(eta(2)-ol )(GL)] by ol' in chloroform [L-L = 2-NC5H4CH=NC(6)H(4)OMe-4; ol' = dim ethyl fumarate (dmf), ol' = acrylonitrile (an), 1-chloro-1-cyanoethyle ne, 1,4-naphthoquinone (nq), tetramethyl ethylenetetracarboxylate (tme tc), fumaronitrile (fn) or maleic anhydride (ma); ol = nq, ol' = tmetc , fn or mal. The substitution equilibria are rapidly established excep t when ol = dmf, nq, ol' = tmetc and were studied by UV/VIS and H-1 NM R spectrometry. The K-c values increase with increasing electron affin ity of the entering activated olefin. The kinetics of slow approach to equilibrium were monitored by UV/VIS techniques at various temperatur es. When ol = dmf, ol' = tmetc; only the second-order rate constant k( 2) for the forward step could be measured with sufficient accuracy, wh ereas for ol = nq, ol' = tmetc the constants for both the forward (k(2 )) and the reverse (k(-2)) steps were determined. Activation parameter s indicate an essentially associative mechanism for these paths.