Synthesis and structures of Pd2M2 (M = Cu, Au) and Pd2M (M = Cu, Ag) mixed-metal complexes supported by NPPN tetradentate ligands

Reactions of [PdCl(Me)(cod)] with two NPPN mixed-donor tetradentate ligands, meso-2-pyridylCH2(Ph)P(CH2)2P(Ph)CH2-2-pyridyl (meso-picppe) and rac-2-pyridylCH2(Ph)P(CH2)4P(Ph)CH2-2-pyridyl (rac-picppb), afforded dinuclear palladium complexes [(PdCl(Me))2(meso-picppe)] (1) and [(PdCl(Me))2(rac-picppb)] (2), which were further converted with 2,6-xylyl isocyanide (XylNC) to [(PdCl(C(NXyl)Me))2(meso-picppe)] (3) and [(PdCl(C(NXyl)Me))2(rac-picppb)] (4) through insertion of XylNC into the Pd–Me bonds. Complexes 3 and 4 possess two imidoyl moieties which are of potential donors and readily capture d10 group 11 metal ions depending on their stereostructures of the NPPN ligands. Reactions of 3 with CuCl or AuCl(tht) afforded Pd2M2 mixed-metal tetranuclear complexes [(PdCl(C(NXyl)Me)(MCl))2(meso-picppe)] (M = Cu (5a), Au (5b)), where each imidoyl moiety captures a MCl fragment in a Ci symmetrical fashion. Similar reactions of 4 with [Cu(MeCN)4]BF4 or AgBF4 resulted in Pd2M trinuclear complexes [(PdCl(C(NXyl)Me)2M(rac-picppb)]BF4 (M = Cu (6a), Ag (6b)), in which two imino groups chelate a MI ion with a pseudo C2 symmetrical structure.