Chemistry of the PCNHCP Ligand: Silver and Ruthenium Complexes, Facial/Meridional Coordination, and Catalytic Transfer Hydrogenation

Abstract

The silver complex of PCNHCP was identified as [Ag3(μ-Cl)(PCNHCP)2]Cl2 (1). Anion exchange of 1 with AgNO3 affords a white compound, which crystallizes into two forms, [Ag3(μ-Cl)(PCNHCP)]2(NO3)2 (2a) and [Ag3(Cl)(NO3)(0.5DMF)(PCNHCP)2]NO3 (2b), from different solvent combinations. Their structural determination reveals interesting structural features, including a short Ag···Ag interaction in both of them. Unlike the common preparation of ruthenium(II) NHC complexes in the literature, a novel silver carbene transfer reaction between 1 and RuCl2(PPh)3 produces fac-[Ru2(μ-Cl)3(PCNHCP)2]Cl (3) in good yield. The nonredox nature of the carbene transfer reaction is different from that of an earlier report and shows that the preparation of divalent ruthenium NHC complexes via silver carbene transfer is a feasible synthetic route. Significantly, complex 3 can also be prepared directly from PCNHCP·HCl and RuCl2(PPh3)3 in the absence of base. Reactions of 3 with CO, phenylacetylene, and pyridine afford mer complexe...