Regioselective competition between the formation of seven-membered and five-membered cyclometalated platinacycles preceded by Csp2[sbnd]Csp3 reductive elimination

Abstract

A mixture of seven-membered and five-membered platinacycle complexes are eventually formed after a series of substitution, oxidative addition, and reductive elimination reactions between the platinum dimer, cis-[Pt2Me4(μ-SMe2)2] and the naphthyl-derived CˆN chelate ligands, (8-XC10H6CH = N-R), X = I, Br; R = phenyl and 4-Cl-benzyl. From the tethered ligand, either an sp2 CH bond can be activated forming a five-membered ring or an sp3 CH bond can be activated forming a seven-membered ring. All compounds have the imine included in the platinacycle. The ratio of complexes as a function of ring size varies depending on ligand architecture of the chelate ligand and the nature of other ligands in the coordination sphere. The cyclometalated platinum complexes have been characterized by NMR spectroscopy. One complex with a seven-membered ring was characterized crystallographically. Reductive elimination reactions of isolated and/or identified cyclometalated, six-membered platinum(IV) compounds [PtMe2Br{C10H6CH = NCH2(4-ClC6H4)}L] and [PtMe2Br{C10H6CH = N(C6H5)}L] (L = SMe2) to form Csp3Csp2 bonds, followed by competition between Csp2H and Csp3H bond activation are also reported.