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

Abstract

Synthesis of PdII and PtII complexes based on the triazolyl-pyridyl phosphine ligand o-Ph2P(C6H4)C(CH)-1,2,3-N3(CH2)(Py) (1) (hereafter referred to as “PՈN3ՈN”) is presented. Reaction of ligand 1 with Pd(COD)Cl2 and Pd(OAc)2 afforded di-coordinated complexes [PdX2{κ2-P,N-(PՈN3ՈN)}] (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-(PՈN3ՈN)}] (4, X = Cl; 5, X = OAc). Treatment of ligand 1 with Pt(COD)Cl2 yielded a P,N-coordinated complex [PtCl2{κ2-P,N- (PՈN3ՈN)}] (6), whereas the same reaction in the presence of a base resulted in the formation of [PtCl{κ3-P,C,N-(PՈN3ՈN)}] (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.