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

Jing Zhang; Jiang-Lin Liang; Xian-Ru Sun; Hai-Bing Zhou; Nian-Yong Zhu; Zhong-Yuan Zhou; Philip Wai Hong Chan; Chi-Ming Che

doi:10.1021/ic0481935

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

Inorg Chem. 2005 May 30;44(11):3942-54. doi: 10.1021/ic0481935.

Authors

Jing Zhang¹, Jiang-Lin Liang, Xian-Ru Sun, Hai-Bing Zhou, Nian-Yong Zhu, Zhong-Yuan Zhou, Philip Wai Hong Chan, Chi-Ming Che

Affiliation

¹ Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China.

PMID: 15907122
DOI: 10.1021/ic0481935

Abstract

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 (H2tBu-salch) and bis(3,5-dibromosalicylidene)-1,2-cyclohexane-diamine (H2Br-salch) are described. Reactions of [Os(VI)tBu-salch)O2] (1a) and [Os(VI)(Br-salch)O2] (1b) with PPh(3), p-X-arylamines (X = NO2, CN), N2H4 x H2O, Ph2NNH2, SOCl2, CF3CO2H, Br2, and I2 under reducing conditions gave [Os(II)(Br-salch)(OPPh3)2] (2), [Os(IV)(Br-salch)(p-X-C6H4NH)2] (3), [mu-O-{Os(IV)(tBu-salch)(p-NO2C6H4NH)}2] (4), [Os(II)(Br-salch)(N2)(H2O)] (5), [Os(IV)(tBu-salch)(OH)(Cl)] (6), [Os(IV)(tBu-salch)(OH)2] (7), [Os(IV)(tBu-salch)Cl2] (8), [Os(IV)(tBu-salch)(CF3CO2)2] (9), [Os(IV)(tBu-salch)Br2] (10), and [Os(IV)(tBu-salch)I2] (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) A for the bis(amido) complexes, Os-Cl distances of 2.333(8)-2.3495(1) A for 6 and 8, Os-O(CF3CO2) distances of 2.025(6)-2.041(6) A for 9, and Os-I distances of 2.6884(6)-2.6970(6) A 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.