Structural and 13C NMR Studies on Palladium MOP Compounds: A New Weak C-Pd -Bond Plus MOP as a Bridging Diene Ligand

A new set of Pd-MOP complexes (MOP = (S)-2-diarylphosphino-1,1′-binaphthyl) has been prepared. One of these, containing MeO-MOP (=2-(diphenylphosphino)-2′-methoxy-1,1′-binaphthyl), is shown to act as a chelating ligand with a naphthyl backbone diene bridging a Pd(I)-Pd(I) bond. This bonding mode exists in both the solid and solution states. A series of chloro-Pd(II)MOP complexes containing the well-known cyclometalated N,N- dimethyl benzylamine chelate have been treated with NaBArF to extract the chloride ligand. The products, starting from the H-MOP, MeO-MOP, and NC-MOP analogues, are all different. Of particular interest is the product from the H-MOP reaction in that the fourth coordination position is occupied by a weak Pd-C a-bond from the naphthyl backbone, on the basis of 13C NMR data. The rate of product formation in the Pd-catalyzed hydrosilylation of styrene with SiHCl3 has been measured as a function of time for the four auxiliaries H-MOP, MeO-MOP, HO-MOP, and NC-MOP. The NC-MOP is shown to be much faster than the others, and a tentative explanation is offered.