Synthesis, Characterization, and Catalytic Activity of Nickel(II) Alkyl Complexes Supported by Pyrrole–Diphosphine Ligands

The organometallic Ni­(II) chemistry of the pyrrole-based pincer ligands (P2RPyr)− (P2RPyr = 2,5-(R2PCH2)2C4H2N, R = Ph, Cy) is reported. Reactions of Grignard reagents with [NiCl­(P2RPyr)] afford a variety of alkyl and aryl complexes (methyl, ethyl, benzyl, phenyl, and allyl) that all display square-planar geometries about nickel. The hydride complex [NiH­(P2CyPyr)] can also prepared either through treatment of [NiCl­(P2CyPyr)] with LiHBEt3 or by reaction of H­(P2RPyr) with [Ni­(COD)2] (COD = 1,4-cyclooctadiene). Reactions of the methyl and hydride complexes with CO and CO2, respectively, evince clean migratory insertion chemistry of the Ni–C and Ni–H bonds. Both the alkyl and chloride complexes are active catalysts for the Kumada coupling of aryl chlorides and aryl or alkyl Grignard reagents at room temperature. The solid-state structures of several of the complexes are reported.