A dioxoruthenium(VI) complex containing a D4-porphyrinato ligand por* H2por* = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4∶5,8-dimethanoanthracen-9-yl]porphyrin} has been prepared by oxidation of its ruthenium(II) carbonyl precursor with m-chloroperoxybenzoic acid and characterised by spectroscopic methods. The [RuVI(por*)O2] complex undergoes enantioselective epoxidation of alkenes and the highest enantiomeric excess (ee) attainable is 77%. In the presence of pyrazole the complex transforms to [RuIV(por*)(pz)2] when reacting with alkenes. The kinetics of the epoxidation of para-substituted styrenes has been studied. The experimental rate law is –d[RuVI]/dt = k2[RuVI][alkene]. The second order rate constants k2 at 25 °C fall in a narrow range, 2.1 × 10–3–9.7 × 10–3 dm3 mol–1 s–1. Comparison of the Hammett plot (log krelvs. σ˙) with those for achiral analogues [RuVI(tpp)O2] (H2tpp = 5,10,15,20-tetraphenylporphyrin) and [RuVI(oep)O2] (H2oep = 2,3,7,8,12,13,17,18-octaethylporphyrin) suggests the formation of a radical intermediate for the alkene epoxidations. Both [RuII(por*)(CO)(EtOH)] and [RuVI(por*)O2] were examined for enantioselective catalysis. Enantioselectivities of the stoichiometric and catalytic reactions showed good correlation. There is no solvent dependence on enantioselectivity when changing the solvent from dichloromethane to benzene.
一种含有
D4-
吡咯环
配体的
二氧化钌(VI)配合物 por* H2por* = 5,10,15,20-四((1S,4R,5R,8S)-1,2,3,4,5,6,7,8-八氢-1,4∶5,8-
二甲基蒽-9-基)
吡咯环} 通过用对
氯过氧
苯甲酸氧化其
钌(II)羰基前体制备,并通过光谱方法表征。复杂的[RuVI(por*)O2]在烯烃的反应中经历了选择性不对称环氧化,所能达到的最高对映体过量(ee)为77%。在
吡唑存在的情况下,该复合物在与烯烃反应时转变为[RuIV(por*)(pz)2]。对对位取代
苯乙烯的环氧化动力学进行了研究。实验速率法则为–d[RuVI]/dt = k2[RuVI][烯烃]。在25°C下的二级速率常数k2落在一个窄范围内,2.1 × 10–3–9.7 × 10–3 dm3 mol–1 s–1。将汉密尔顿图(log krel与σ˙的关系)与无手性的类似物[RuVI(tpp)O2](H2tpp = 5,10,15,20-四苯基
吡咯环)和[RuVI(oep)O2](H2oep = 2,3,7,8,12,13,17,18-八乙基
吡咯环)进行比较,提示在烯烃的环氧化过程中形成了自由基中间体。对[RuII(por*)(CO)(EtOH)]和[RuVI(por*)O2]进行了手性选择性催化的研究。计量反应和催化反应的手性选择性表现出良好的相关性。当溶剂从
二氯甲烷更换为苯时,手性选择性不受溶剂的影响。