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 (P(2)(R)Pyr)(-) (P(2)(R)Pyr = 2,5-(R2PCH2)(2)C4H2N, R = Ph, Cy) is reported. Reactions of Grignard reagents with [NiCl(P(2)(R)Pyr)] 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(P(2)(C)yPyr)] can also prepared either through treatment of [NiCl(P(2)(C)yPyr)] with LiHBEt3 or by reaction of H(P(2)(R)Pyr) 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.