Pd-II and Pt-II Complexes of 2-(2 '-Pyridyl)-4,6-diphenylphosphinine: Synthesis, Structure, and Reactivity

The coordination chemistry of the bidentate P,N hybrid ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (1) towards Pd-II and PtII has been investigated. The molecular structures of the complexes [PdCl2(1)] and [PtCl2(1)] were determined by X-ray diffraction, representing the first crystallographically characterized lambda(3)-phosphinine-Pd-II and -Pt-II complexes. Both complexes reacted with methanol at the P=C double bond at an elevated temperature, leading to the corresponding products [MCl2(1H center dot OCH3)]. The molecular structure of [PdCl2(1H center dot OCH3)] was determined crystallographically and revealed that the reaction with methanol proceeds selectively by syn addition and exclusively to one of the P=C double bonds. Strikingly, the reaction of [PdCl2(1H center dot OCH3)] with the chelating diphosphine DPEphos at room temperature in CH2Cl2 led quantitatively to [PdCl2(DPEphos)] and phosphinine 1 by elimination of CH3OH and rearomatization of the phosphorus heterocycle.