Cyclopalladation of meta-(Diphenylthiophosphoryloxy)benzaldimines: NCS and Unexpected NCO 5,6-Membered Pincer Palladium Complexes

Unsymmetrical NCS -pincer ligands of a new type, namely, m -(diphenylthiophosphoryloxy)benzaldimines 3 (1-[Ph 2 P(S)O]-3-[CH═NR]-C 6 H 4, R = OMe ( 3a ), Ph ( 3b ), t Bu ( 3c )), were obtained in two steps starting from commercially available 3-hydroxybenzaldehyde. These ligands easily underwent cyclopalladation at the C-2 position of the central benzene ring in the reaction with PdCl 2 (PhCN) 2 in benzene or benzene−methanol solutions to afford the corresponding hybrid pincer complexes 4a − c with five- and six-membered fused metallacycles in moderate to good yields. The same reaction in dichloromethane followed by treatment with alcohol resulted in unexpected formation of the related NCO -palladacycles 5a, b, along with the above NCS -complexes. Complexes 5 present the products of formal oxidation of the P═S group in the starting ligand, which apparently proceeds in the metal ion coordination sphere. Realization of κ 3 - NCS and κ 3 - NCO coordination in 4a − c and 5a, b, respectively, was unambiguously confirmed by X-ray diffraction analysis as well as multinuclear ( 1 H, 13 C, 31 P) NMR, IR, and Raman spectroscopy. The NCS -pincer complexes 4a − c demonstrated excellent catalytic activity for the Suzuki cross-coupling reactions of aryl halides with phenylboronic acid.