Syntheses and structures of nickel(0) complexes containing the methyl methacrylate monomer as ligand

Abstract

The reaction of [Ni(η⁴-C₈H₁₂)₂] with the industrially important monomer methyl methacrylate, CH₂C(Me)CO₂Me, in the presence of 1 or 2 mol equivalents of tricyclohexylphosphine leads to the formation of [Ni{η²-CH₂C(Me)CO₂Me}{P(C₆H₁₁)₃}₂]1 and [Ni{η²-CH₂C(Me)CO₂Me}₂{P(C₆H₁₁)₃}]2, respectively. The crystal structures of 1 and 2 have been determined and reveal an η²-CC mode of co-ordination of the methyl methacrylate ligands, with the CO₂Me groups pendant and outside the nickel co-ordination sphere. Complexes 1 and 2 represent the first structurally characterised methyl methacrylate complexes; 2 is formed as a mixture of meso and DL diastereomers in the ratio 2.34:1. Solution NMR studies indicate that the diastereomers interconvert rapidly, via an intramolecular mechanism, which is proposed to proceed via an O-co-ordinated intermediate. Reaction of 1 with an excess of tert-butyl acrylate CH₂CHCO₂Bu^t yields [Ni(η²-CH₂CHCO₂Bu^t)₂{P(C₆H₁₁)₃}]4, which may be prepared independently from [Ni(η⁴-C₈H₁₂)₂], P(C₆H₁₁)₃ and tert-butyl acrylate.