Novosibirsk State University, Ul. Pirogova 2, Novosibirsk 630090, Russian Federation.
Inorg Chem. 2010 Sep 20;49(18):8620-8. doi: 10.1021/ic101297x.
The catalytic properties of a series of chiral nonheme aminopyridinylmanganese(II) complexes [LMn(II)(OTf)(2)] were investigated. The above complexes were found to efficiently catalyze enantioselective olefin oxidation to the corresponding epoxides with different oxidants (peroxycarboxylic acids, alkyl hydroperoxides, iodosylarenes, etc.) with high conversions and selectivities (up to 100%) and enantiomeric excesses (up to 79%). The effect of the ligand structure on the catalytic performance was probed. Epoxidation enantioselectivities were found to be strongly dependent on the structure of the oxidants (performic, peracetic, and m-chloroperbenzoic acids; tert-butyl and cumyl hydroperoxides; iodosylbenzene and iodosylmesitylene), thus bearing evidence that the terminal oxidant molecule is incorporated in the structure of the oxygen-transferring intermediates. High-valence electron-paramagnetic-resonance-active manganese complexes LMn(IV)═O and LMn(IV)(μ-O)(2)Mn(III)L were detected upon interaction of the starting catalyst with the oxidants. The high-valence complexes did not epoxidize styrene and could themselves only contribute to minor olefin oxidation sideways. However, the oxomanganese(IV) species were found to perform the Lewis acid activation of the acyl and alkyl hydroperoxides or iodosylarenes to form the new type of oxidant [oxomanganese(IV) complex with a terminal oxidant], with the latter accounting for the predominant enantioselective epoxidation pathway in the nonheme manganese-catalyzed olefin epoxidations.
研究了一系列手性非血红素氨基吡啶基锰(II)配合物[LMn(II)(OTf)(2)]的催化特性。发现上述配合物可以有效地催化烯烃的对映选择性氧化，使用不同的氧化剂（过氧羧酸、烷基过氧化物、碘代苯等），转化率和选择性高（高达 100%），对映体过量（高达 79%）。还探究了配体结构对催化性能的影响。发现环氧化的对映选择性强烈依赖于氧化剂的结构（过氧甲酸、过氧乙酸和间氯过氧苯甲酸；叔丁基和cumyl 过氧化物；碘代苯和碘代均三甲苯），因此证明末端氧化剂分子被整合到氧转移中间体的结构中。在起始催化剂与氧化剂相互作用时，检测到高氧化态电子顺磁共振活性锰配合物LMn(IV)═O和LMn(IV)(μ-O)(2)Mn(III)L。高价配合物不能环氧化苯乙烯，只能对烯烃的次要氧化起作用。然而，发现氧化锰(IV)物种可以对酰基和烷基过氧化物或碘代苯进行路易斯酸活化，形成新型氧化剂[末端氧化剂的氧化锰(IV)配合物]，后者是手性锰催化烯烃环氧化中非血红素锰催化烯烃环氧化的主要对映选择性环氧化途径。
