Synthesis and Luminescence Properties of Cycloplatinated Complexes with a Chelating N super()C Pyridine-Derived N-Heterocyclic Carbene - Influence of 2,4,6-Triphenyl-phosphinine versus Triphenylphosphine

Two cycloplatinated complexes of the form [Pt(NC)CH sub(3)(P)] super( +) incorporating a rare, bidentate NC-chelating pyridylpyridylidene ligand are reported. The phosphorus-based ligand P is either 2,4,6-triphenylphosphinine or triphenylphosphine. These mononuclear complexes have been fully characterised in solution and by single-crystal X-ray diffraction analysis. UV/Vis absorption and photoluminescence spectroscopy studies reveal strong phosphorescence from the phosphinine compound at 77 K but no emission from its triphenylphosphine analogue. This contrasting behaviour can be traced to the pi -acceptor ability of the phosphabenzene ring, as corroborated by electrochemical and time-dependent DFT (TD-DFT) calculations. Two cycloplatinated complexes with a rare bidentate pyridylpyridylidene NC ligand and triphenylphosphine or 2,4,6-triphenylphosphinine coligands are synthesised and characterised. The phosphinine compound is strongly phosphorescent at 77 K, in contrast to the triphenylphosphine counterpart; this behaviour is probably the result of the exceptional pi -acceptor ability of the phosphabenzene ring.