Stereoselectivity in organometallic reactions: Intramolecular oxidative addition of aryl-halogen bonds to platinum(II)

The degree of stereoselectivity in intramolecular oxidative addition of aryl-halogen bonds to platinum(II) has been determined using the following diimine ligands based on trans-or cis-1,2-diaminocyclohexane, trans-1,2-(N=CHC6H4X)(2)C6H10 (X = Br, Cl), and cis-1,2-(N=CHC6H4Br)(2)C6H10. Reaction pf trans-1,2-(N=CHC6H4X)(2)C6H10 (X = Br, Cl) with [Pt2Me4(mu-SMe2)(2)] gave the isomerically pure binuclear complexes [Pt2Me4X2(mu-SMe2){trans-1,2-(N=CHC6H4)(2)C6H10}], which on further reaction gave the complexes [Pt2Me4(mu-X)(2){trans-1,2-(N=CHC6H4)(2)C6H10}] by loss of Me2S. The products are formed by oxidative addition of both aryl-halogen bonds of the diimine, yielding a novel chiral tetradentate N2C2-donor ligand. The ligand cis-1,2-(N=CHC6H4Br)(2)C6H10 reacted with [Pt2Me4(mu-SMe2)(2)] to give mononuclear platinum(IV) products of the type [PtBrMe2{cis-l,2-(N=CHC6H4)(N=CHC6H4Br)C6H10}] With approximately 90% stereoselectivity and [PtBrMe2(SMe2){cis-1,2-(N=CHC6H4)(N=CHC6H4Br)C6H10}], and these reactions involve oxidative addition of only one of the aryl-halogen bonds. H-1 NMR spectroscopy was used to characterize the new complexes and to establish diastereomeric ratios. The structures of complexes [Pt2Me4Br2(mu-SMe2){trans-1,2-(N=CHC6H4)(2)C6H10},,] (3a), [Pt2Me4(mu-Br)(2)({trans-1,2-(N=CHC6H4)(2)C6H10}] (4a), and [PtBrMe2{cis-1,2-;(N=CHC6H4)(N=CHC6H4Br)C6H10}] (6a') have been established by X-ray structure, determinations.