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, CH2 C(Me)CO2Me, in the presence of 1 or 2 mol equivalents of tricyclohexylphosphine leads to the formation of [Ni{η2-CH2 C(Me)CO2Me}{P(C6H11)3}2]1 and [Ni{η2-CH2 C(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 CH2 CHCO2But yields [Ni(η2-CH2 CHCO2But)2{P(C6H11)3}]4, which may be prepared independently from [Ni(η4-C8H12)2], P(C6H11)3 and tert-butyl acrylate.

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