Stepwise cyclopalladation of 2-phenacylthiopyridine to give C,C,N-pincer complexes

Abstract

Orthopalladation of the phenyl ring in the cyclopalladated complex [Pd{C,N-pyl-SCHC(O)Ph}(μ-X)]₂ (pyl = 2-pyridyl, X = Cl; 1·Cl) occurs upon reacting it with AgOAc (1 : 2) in MeCN to give the pincer complex [Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(NCMe)] (2). The nature of the base and X plays a key role because palladation neither occurs with other bases nor when AgOAc is the base and X is Br, in which case 1·OAc is obtained. In addition, complex 2 is not obtained upon refluxing 1·OAc in MeCN. Complex 2 affords complexes [Pd{C,C,N,S-pyl-SCHC(O)C₆H₄-2}]_n, [Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}L] (L = PPh₃, ^tBuNC, XyNC) or Me₄N[Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}Cl] upon acetonitrile loss, or its replacement by neutral or anionic ligands, respectively. Some such complexes act as metallaligands towards AgClO₄ or [PdCl₂(NCPh)₂] giving rise to heterodinuclear [{Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(PPh₃)}{Ag(PPh₃)}]ClO₄ or homodinuclear [{Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(Cl)}{Pd(μ-Cl)}]₂, [{Pd{C,C,N-pyl-SCHC(O)C₆H₄-2}(Cl)}{Pd(Cl)(PPh₃}] complexes. Some derivatives of complexes 1 were also obtained.