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

摘要

Ligand exchange reactions have been used for the synthesis of metallacyclic complexes of Ni and Pd of the type [M(CH_2CMe_2-o-C _6H_4)(P-N)], where P-N is the phosphinito-imine ligand P(iPr)_2OC(Me)N(2,6-C_6H_3(iPr)_2. The protic acid [H(OEt_2)(BAr′_4)] (Ar′ = 3,5-C _6H_3(CF_3)_2) selectively cleaves one of the two σ metal-carbon bonds, affording cationic monoalkyl complexes. Nickel monoalkyls stabilized with Et_2O 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.