Migratory insertion reactions of nickel and palladium σ-alkyl complexes with a phosphinito-imine ligand†‡

Abstract

Ligand exchange reactions have been used for the synthesis of metallacyclic complexes of Ni and Pd of the type [M[upper bond 1 start](CH2CMe2-o-C6[upper bond 1 end]H4)(P–N)], where P–N is the phosphinito-imine ligand P(iPr)2OC(Me)[double bond, length as m-dash]N(2,6-C6H3(iPr)2. The protic acid [H(OEt2)(BAr′4)] (Ar′ = 3,5-C6H3(CF3)2) selectively cleaves one of the two σ metal–carbon bonds, affording cationic monoalkyl complexes. Nickel monoalkyls stabilized with Et2O or MeCN ligands are thermally unstable and spontaneously undergo a decomposition process that ultimately leads to the breakdown of the phosphinito-imine ligand. In contrast, cationic alkylpalladium derivatives are thermally very stable, allowing the isolation of a formally unsaturated monoalkyl complex stabilized by an intramolecular π-arene interaction. Although monoalkynickel and -palladium phosphinito-imine derivatives are inactive as ethylene polymerization or copolymerization catalysts, they readily experience migratory insertion reactions. A palladium chelate arising from the successive insertion of CO and ethylene has been isolated and characterized.