CHEMISTRY AND KINETICS OF COUPLING REACTIONS OF CO AND ALKENES MEDIATED BY PD(II) COMPLEXES

Studies have been carried out on model systems closely mimicking the i ntimate steps of the homogeneous catalytic cycle involving the perfect ly alternating coupling of CO and alkenes and leading to polyketones m ediated by Pd(II) compounds. Kinetic investigations of the reaction of (Ar-BIAN)Pd(C(O)R)X (Ar-BIAN = bis(arylimino) acenaphthene: X = Cl, B r, I; R = Me, Et, i-Pr, Ph) with norbornadiene (nbd) showed that under pseudo-first-order conditions with an excess of nbd the k(abs) follow s the rate law k(1) + k(2)[nbd]. From the influence of the halide X, e xcess X-, the type of R substituent, the steric and electronic propert ies of Ar-BIAN, excess Ar-BIAN, and the solvent it was concluded that the nbd-independent pathway (k(1)) and the nbd-dependent pathway (k(2) ) may follow routes that depend on whether, in the substitution step(s ) preceding the insertion step, the halide or one of the N atoms of th e Ar-BIAN ligand is substituted by nbd. Isonitriles can also be insert ed in the complexes (N-N)Pd(Me)X (N-N=bipy, phen; X = Cl-) to give the complexes (N-N)Pd(C(= NR)Me)X, which react further with nbd, ethene, and propene to give the stable complexes [(N-N)Pd(alkene-C(= NR)Me]X. Finally, [(terpy)PdMe]Cl complexes insert CO rapidly and subsequently insert nbd very rapidly to afford [(terpy) Pd(nbd-C(O)Me)]X-.