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

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, (t)BuNC, 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.