Stereoselectivity in Organometallic Reactions: Intramolecular Oxidative Addition of Aryl−Halogen Bonds to Platinum(II)

Abstract

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-(NCHC6H4X)2C6H10 (X = Br, Cl), and cis-1,2-(NCHC6H4Br)2C6H10. Reaction of trans-1,2-(NCHC6H4X)2C6H10 (X = Br, Cl) with [Pt2Me4(μ-SMe2)2] gave the isomerically pure binuclear complexes [Pt2Me4X2(μ-SMe2){trans-1,2-(NCHC6H4)2C6H10}], which on further reaction gave the complexes [Pt2Me4(μ-X)2{trans-1,2-(NCHC6H4)2C6H10}] 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-(NCHC6H4Br)2C6H10 reacted with [Pt2Me4(μ-SMe2)2] to give mononuclear platinum(IV) products of the type [PtBrMe2{cis-1,2-(NCHC6H4)(NCHC6H4Br)C6H10}] with approximately 90% stereoselectivity and [PtBrMe2(SMe2){cis-1,2-(NCHC6H4)(NCHC6H4Br)C6H10}], and these reactions involve oxidative addition of only one of the aryl−halogen bonds. 1H NMR spectroscopy was used to characterize the new complexes and to establish diastereomeric ratios. The structures of complexes [Pt2Me4Br2(μ-SMe2){trans-1,2-(NCHC6H4)2C6H10}] (3a), [Pt2Me4(μ-Br)2{trans-1,2-(NCHC6H4)2C6H10}] (4a), and [PtBrMe2{cis-1,2-(NCHC6H4)(NCHC6H4Br)C6H10}] (6a‘) have been established by X-ray structure determinations.