Chiral osmium complexes with sterically bulky Schiff-base ligands. Crystal structures of Os(IV) derivatives and the reactivity and catalytic cyclopropanation of alkenes with EDA

The syntheses and reactivities of sterically encumbered trans-dioxoosmium(VI) complexes containing Schiff-base ligands bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamine (H2Bu-salch) and bis(3,5-dibromosalicylidene)-1,2cyclohexane-diamine (H-2-Br-salch) are described. Reactions of [Os-Vl(Bu-salch)O-2] (1a) and [Os-Vl(Br-salch)O-2] (1b) with PPh3, p-X-arylamines (X = NO2, CN), (N2H4H2O)-H-., Ph2NNH2, SOCl2, CF3CO2H, Br-2, and I-2 under reducing conditions gave [Os-II(Br-salch)(OPPh3)(2)] (2), [Os-IV(Br-salch)(p-X-C6H4NH)(2)] (3), [mu-O-(Os-IV('Bu-salch)(p-NO2C6H4 -NH)(2)] (4), [Os-II[Br-salch)(N-2)(H2O)] (5), [Os-IV(Bu-t-salch)(OH)(Cl)] (6), [Os-IV(Bu-salch)(OH)(2)] (7), [Os-IV(Bu-salch)-Cl-2 (8), [Osr(IV)(Bu-salch)(CF3CO2)(2)] (9), [Os-IV(Bu-salch)Br-2] (10), and [Os-IV(Bu-salch)l(2)] (11), respectively. X-ray crystal structure determinations of [Os-IV(Br-salch)(P-NO2C6H4NH)(2)] (3a), [Os-IV(Br-salch)(p-CNC6H4NH)(2)] (3b), 6, 8, 9, and 11 reveal the Os-N(amido) distances to be 1.965(4)-1.995(1) angstrom for the bis(amido) complexes, Os-Cl distances of 2.333(8)-2.3495(1) angstrom for 6 and 8, Os-O(CF3CO2) distances of 2.025(6)-2,041(6) angstrom for 9, and Os-I distances of 2.6884(6)-2.6970(6) angstrom for 11. Upon UV irradiation, (1S,2S)-(1a) reacted with aryl-substituted alkenes to give the corresponding epoxides in moderate yields, albeit with no enantioselectivity, The (1R,2R)-6 catalyzed cyclopropanation of a series of substituted styrenes exhibited moderate to good enantioselectivity (up to 79% ee) and moderate trans selectivity.