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.