STEREOSELECTIVITY IN ORGANOMETALLIC REACTIONS - INTRAMOLECULAR OXIDATIVE ADDITION OF ARYL-HALOGEN BONDS TO PLATINUM(II)

The degree of stereoselectivity in intramolecular oxidative addition o f aryl-halogen bonds to platinum(II) has been determined using the fol lowing diimine ligands based on trans-or cis-1,2-diaminocyclohexane, t rans-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 [Pt 2Me4(mu-SMe2)(2)] gave the isomerically pure binuclear complexes [Pt2M e4X2(mu-SMe2){trans-1,2-(N=CHC6H4)(2)C6H10}], which on further reactio n gave the complexes [Pt2Me4(mu-X)(2){trans-1,2-(N=CHC6H4)(2)C6H10}] b y loss of Me2S. The products are formed by oxidative addition of both aryl-halogen bonds of the diimine, yielding a novel chiral tetradentat e N2C2-donor ligand. The ligand cis-1,2-(N=CHC6H4Br)(2)C6H10 reacted w ith [Pt2Me4(mu-SMe2)(2)] to give mononuclear platinum(IV) products of the type [PtBrMe2{cis-l,2-(N=CHC6H4)(N=CHC6H4Br)C6H10}] With approxima tely 90% stereoselectivity and BrMe2(SMe2){cis-1,2-(N=CHC6H4)(N=CHC6H4 Br)C6H10}], and these reactions involve oxidative addition of only one of the aryl-halogen bonds. H-1 NMR spectroscopy was used to character ize the new complexes and to establish diastereomeric ratios. The stru ctures of complexes t2Me4Br2(mu-SMe2){trans-1,2-(N=CHC6H4)(2)C6H10},,] (3a), [Pt2Me4(mu-Br)(2)({trans-1,2-(N=CHC6H4)(2)C6H10}] (4a), and [Pt BrMe2{cis-1,2-;(N=CHC6H4)(N=CHC6H4Br)C6H10}] (6a') have been establish ed by X-ray structure, determinations.