Keywords: Density functional calculations / Homogeneous catalysis / P ligands / Ruthenium / Palladium / S ligands 1,3,2-Diazaphosphinine (1) reacts successively with diphenylacetylene and diphenyl(1-propynyl)phosphane sulfide to afford the P,S-bidentate phosphinine 3. Reaction of nBuLi with 3 followed by complexation with [RuCl 2 (C 10 H 14 )] 2 gave two diastereoisomers 5a,b. Variable-temperature NMR spectroscopy and ONIOM DFT calculations were carried out to rationalize their formation. Complexes 5a,b were used as catalysts in hydrogen-transfer hydrogenation (TON up to