CARBENE-TYPE AMIDOOSMIUM COMPLEXES WITH AN OS-N DOUBLE-BOND - SYNTHESIS, STRUCTURE AND REACTIVITY OF [(MES)OS(=NHR)(PIPR3)]PF6

The reaction of [(Mes)Os(PiPr3)Cl2] (1) (Mes = 1,3,5-C6H3Me3) with primary amines RNH2 (R = Ph, Me, Et) in acetone/water (1:1) gives, after addition of KPF6, the amidoosmium(II) complexes [(Mes)Os(=NHR)(PiPr3)]PF6 (2-4) in 60-80% yield. From 1 and Et2NH, the chloro(hydrido)compound [(Mes)OsH(PiPr3)Cl] (5) is formed. The X-ray structural analysis of 2 reveals that the geometry around the osmium atom is trigonal-planar (with the midpoint of the mesitylene ring as one coordination site) and that the Os-N distance of 1.923(4) angstrom is in agreement with an Os-N double bond. Thermolysis of 4 (R = Et) at 165-degrees-C leads to the formation of the aldimino(hydrido)osmium complex [(Mes)OsH(NH=CHMe)(PiPr3)]PF6 (6) by beta-hydride migration from the NCH2 carbon atom to the metal atom. Protonation of 3 (R = Me) with HCl gives the amine complex [(Mes)Os(NH2Me)(PiPr3)Cl]PF6 (7), whereas on treatment of 3 and 4 with CD3NO2 the deuterated derivatives [(Mes)Os(=NDR)(PiPr3)]PF6 ([D1]-3, [D1]-4) are almost quantitatively formed. Compound 2 (R = Ph) reacts with KOtBu by proton abstraction and phosphane elimination to give the dinuclear imidoosmium complex [(MeS)2Os2(mu-NPh)2] (8).