Synthesis and characterization of new Pd(II) non-symmetrical Pincer complexes derived from thioether functionalized iminophosphoranes. Evaluation of their catalytic activity in the Suzuki-Miyaura couplings

The iminophosphorane ligands (Ph3P=NC6H4SR) [R = CH3 (1) and C6H5 (2)] were easily synthesized from triphenylphosphine and 2-(methylthio)aniline or 2-(phenylthio) aniline respectively by the Horner and Oediger variation of the Kirsanov reaction. The reactivity of both ligands was explored with [Na2PdCl4] to afford the corresponding non-symmetric iminophosphorane pincer derivatives [PdCl{C6H4(Ph2P=NC6H4SR-kappa(3)-C,N,S)}] [R = CH3 (3) and C6H5 (4)]. A careful monitoring of the reaction by P-31 {H-1} NMR experiments revealed the N, S chelated species [PdCl2{C6H4(Ph2P=NC6H4SR-kappa(2)-N,S)}] [R = CH3 (5) and C6H5 (6)] to be stable intermediates through the formation of the pincer compounds. Thus, carrying out the reaction for the attaining of (4) at room temperature allowed the isolation and full characterization of the chelated complex [PdCl2{C6H4(Ph2P=NC6H4SPh-kappa-N,S)}] (6). All above mentioned species were unequivocally characterized by single crystal X-ray diffraction experiments. In addition, the newly synthesized pincer complexes [PdCl{C6H4(Ph2P=NC6H4SR-kappa(3)-C,N,S)}] [R = CH3 (3) and C6H5 (4)] were tested as catalyst, proven to be efficient in the Suzuki-Miyaura C-C cross coupling reactions of a series of para-substituted bromobenzenes. (C) 2013 Elsevier B. V. All rights reserved.