title: A silica gel-supported ruthenium complex of 1,4,7-trimethyl-1,4,7-triazacyclononane as recyclable catalyst for chemoselective oxidation of alcohols and alkenes by tert-butyl hydroperoxide.
abstract: A silica gel-immobilized [(Me(3)tacn)Ru(III)(CF(3)COO)(2)(H(2)O)]CF(3)CO(2) complex (1-SiO(2), Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) was prepared by simple impregnation, and the catalyst was characterized by powdered X-ray diffraction, nitrogen adsorption/desorption, Raman, and diffuse reflectance UV-vis spectroscopies. The supported Ru catalyst can effect facile oxidation of alcohols by tert-butyl hydroperoxide (TBHP). Primary and secondary benzyl, allylic, and propargylic alcohols were transformed to their corresponding aldehydes and ketones in excellent yields; no oxidation of the C=C and Ctbd1;C bonds was observed for the allylic and propargylic alcohol oxidations. Likewise alkene epoxidation by TBHP can be achieved by 1-SiO(2); cycloalkenes such as norbornene and cyclooctene were oxidized to their exo-epoxides exclusively in excellent yields (>95%). The 1-SiO(2) catalyst can be recycled and reused for consecutive alcohol and alkene oxidations without significant loss of catalytic activity and selectivity; over 9000 turnovers have been attained for the oxidation of 1-phenyl-1-propanol to 1-phenyl-1-propanone. 4-Substituted phenols were oxidized by the "1 + TBHP" protocol to give exclusively ruthenium-catecholate complexes, which were characterized by UV-vis and ESI-MS spectroscopies. No (tert-butyldioxy)cyclohexadienone and other radical coupling/overoxidation products were produced using the "1 + TBHP" protocol. The formation of ruthenium-catecholate is proposed to proceed via ortho-hydroxylation of phenol.
authors.affiliation: 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.
authors.forename: Wai-Hung
authors.initials: WH
authors.lastname: Cheung
authors.forename: Wing-Yiu
authors.initials: WY
authors.lastname: Yu
authors.forename: Wing-Ping
authors.initials: WP
authors.lastname: Yip
authors.forename: Nian-Yong
authors.initials: NY
authors.lastname: Zhu
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che