Pd(II) and Pt(II) complexes of cyclic bidentate (S)PNP(S) ligands: Synthesis, structure and catalytic activity in the Suzuki reaction

The synthetic approach to the novel cyclic (S)PNP(S) ligands (5a–c, R = EtO, Me, Ph), i.e. 1-thiophosphoryl-2-thioxo-1,2-azaphospholanes having different surrounding at the exocyclic phosphorus atom, has been developed. Compounds bearing two asymmetric phosphorus atoms were obtained as individual (R∗,R∗)- and (R∗,S∗)-diastereomers. Reacting with (PhCN)2MCl2 (M = Pd, Pt) in MeCN under ambient conditions the ligands readily form complexes MLCl2 [6a–c (M = Pd), 7b (M = Pt)] via bidentate chelating coordination mode. The structures and stereochemistry both of the ligands and their complexes were confirmed by IR, multinuclear NMR and X-ray diffraction study. The palladium complexes demonstrated high activity as precatalysts for the Suzuki cross-coupling reaction, which was found to increase in the series 6a < 6b < 6c.