Triazolyl–phosphine with pyridyl functionality: PdII/PtII complexes and selective transfer semi-hydrogenation of alkynes using ethanol as a hydrogen source

Abstract

Synthesis of Pd^II and Pt^II complexes based on the triazolyl-pyridyl phosphine ligand o-Ph₂P(C₆H₄)C(CH)-1,2,3-N₃(CH₂)(Py) (1) (hereafter referred to as “P^∩N₃^∩N”) is presented. The reaction of ligand 1 with Pd(COD)Cl₂ and Pd(OAc)₂ afforded di-coordinated complexes [PdX₂{κ²-P,N-(P^∩N₃^∩N)}] (2, X = Cl; 3, X = OAc). Upon heating, complexes 2 and 3 underwent C–H activation to yield pincer complexes [PdX{κ³-P,C,N-(P^∩N₃^∩N)}] (4, X = Cl; 5, X = OAc). Treatment of ligand 1 with Pt(COD)Cl₂ yielded a P,N-coordinated complex [PtCl₂{κ²-P,N-(P^∩N₃^∩N)}] (6), whereas the same reaction in the presence of a base resulted in the formation of [PtCl{κ³-P,C,N-(P^∩N₃^∩N)}] (7). DFT calculations were carried out to gain mechanistic insights into the transformation of complex 2 to 4, aiming to identify and characterize the key intermediate involved in the C–H activation process. In situ-generated Pd nanoparticles stabilized by ligand 1 catalysed the selective semi-hydrogenation of alkynes to Z-alkenes using ethanol as the hydrogen source.