Palladium(II) allyl complexes with potentially terdentate ancillary ligands. Mechanism of allyl amination by piperidine
摘要:
The reactivity of palladium(II) allyl complexes containing potentially terdentate ligands toward allyl amination was studied in CHCl3 in the presence of the activated olefin fumaronitrile. The influence of different L-L'-L terdentate ligands on the fluxionality in solution and on the reactivity was discussed. Quite surprisingly the behavior of S-N-S, N-S-N and N-N-N ligands is very similar to that of the corresponding N-S and N-N bidentate ligands. In these cases the conventional stepwise mechanism is observed which involves a fast pre-equilibrium in which the terdentate ligand is displaced by the entering amine and the concomitant rate-determining bimolecular attack of the amine itself to give the final allylamine and the olefin-stabilized Pd(0) complex. At variance, the P-N-N ligand imparts to the allyl complex a reactivity similar to that of the corresponding complexes containing a strongly hindered bidentate P-N species, from which the ligand is not displaced thanks to the strongly bound phosphine group. (C) 1999 Elsevier Science S.A. All rights reserved.