α,β-Unsaturated Carbonyl Compounds as Hard/Soft Chelating Ligands in Methyl Nickel Phenolates and the Structure of <i>trans</i>-Methyl-2-(3-phenyl-2,3-η<sup>2</sup>- propenoyl)phenolatobis(trimethylphosphine)nickel(II)

Phenolato functions of chalcone type compounds may replace both methoxo bridges in dinuclear methyl nickel complexes without utilizing the aldehyde functions. Cleavage of phenolato-bridged nickel(II) centers in square planar coordination geometry by addition of trimethylphosphine affords mononuclear methylnickel complexes of coordination number five. The trimethylphosphine-supported trigonal bipyramidal methyl nickel(II) complex has a hard/soft chelating ligand with a phenolato oxygen atom and a π-coordinated olefin functional group. The chemical reactivity of complexes with these novel hard/soft chelating ligands remains to be clarified.