1H NMR and EPR spectroscopic monitoring of the reactive intermediates of (Salen) MnIII catalyzed olefin epoxidation
1H NMR and EPR spectroscopic monitoring of the reactive intermediates of (Salen) MnIII catalyzed olefin epoxidation
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DOI：
10.1016/s1381-1169(00)00040-6
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发表时间：
2000-09-08
影响因子：
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通讯作者：
Talsi, EP
中科院分区：
文献类型：
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作者：
Bryliakov, KP;Babushkin, DE;Talsi, EP
利用H-1核磁共振和EPR光谱，研究了1 +碘索苯（PhIQ）及其间氯过氧苯甲酸（m-CPBA）催化体系中形成的锰种，其中1为（R，R）-(-)-N， N'-双（3,5-二叔丁基水杨基）-1,2环己二胺-氯化锰（[(Salen)Mn-III]）。在1 + PhIO催化体系中表征了三种类型的锰配合物（4-6）。配合物4非常不稳定，在- 20℃时与苯乙烯反应生成苯乙烯氧化物。它在1.68、1.64和1.42 ppm处显示出三个tBu基团的信号。这种模式与模型复合体[(Salen)Mn-V = N]的模式非常相似。根据这些数据，4被鉴定为d(2)低自旋氧锰(V)配合物[(Salen)Mn-V = O]（+）。配合物5和6在-20℃时相对稳定，在此温度下对苯乙烯反应性差。它们具有反铁磁偶联mu-氧-双核Mn-IV的H-1核磁共振谱特征，被鉴定为双核配合物[(Salen)LMnIV-O-Mn-IV(Salen)L']， L' = Cl-和PhIO。EPR发现，在CH2Cl2中，1与m-CPBA相互作用的第一阶段形成了酰基过氧配合物（Salen）Mn-III(OOCOAr)(7)。配合物7不稳定，可转化为锰（IV）氧配合物[(Salen)Mn-IV(O)](8)。在-70℃下，该反应的一级速率常数为0.25 +/- 0.08 min（-1）。在-70℃下，配合物7与苯乙烯反应的速率常数为1.1 +/- 0.4 M-1 min(-1)，生成环氧化物并还原1。配合物8在低温下对苯乙烯是惰性的。研究了给体n -甲基- n -氧化物（NMO）对苯乙烯在1 + m-CPBA体系中的环氧化反应的影响。在与m-CPBA相互作用之前，在CH2Cl2中的1溶液中加入NMO（2-5等量），可以显著提高反应性酰基过氧配合物7-NMO向相对惰性氧配合物-8-NMO的不良转化速率。然而，在苯乙烯存在的情况下，8-NMO与苯乙烯的快速反应产生苯乙烯氧化物并恢复1-NMO，完全抑制了这种不良转化。(C) 2000 Elsevier Science B.V.版权所有
Using H-1 NMR and EPR spectroscopy, manganese species formed in the catalytic systems 1 + iodosobenzene (PhIQ) and it meta-chloroperoxybenzoic acid (m-CPBA), where 1 is (R,R)-(-)-N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2 cyclohexanediamino-manganese(III) chloride ([(Salen)Mn-III]) were studied. Three types of manganese complexes were characterized in the catalytic system 1 + PhIO (4-6). Complex 4 is very unstable and reacts with styrene at - 20 degrees C to afford styrene oxide. It exhibits three signals of tBu groups at 1.68, 1.64 and 1.42 ppm. This pattern closely resembles that for a model complex [(Salen)Mn-V = N]. Based on these data, 4 was identified as d(2) low-spin oxomanganese(V) complex [(Salen)Mn-V = O](+). Complexes 5 and 6 are relatively stable at -20 degrees C and poorly reactive towards styrene at this temperature. They display H-1 NMR spectra characteristic for antiferromagnetically coupled mu-oxo-dinuclear Mn-IV species and are identified as dinuclear complexes [(Salen)LMnIV-O-Mn-IV(Salen)L'] with L, L' = Cl- and PhIO. It was found by EPR that the acylperoxo complex (Salen)Mn-III(OOCOAr) (7) was formed at the first stage of the interaction of 1 with m-CPBA in CH2Cl2. Complex 7 is unstable and converts into manganese(IV) oxo complex [(Salen)Mn-IV(O)] (8). The evaluated first order rate constant of this conversion is 0.25 +/- 0.08 min(-1) at -70 degrees C. Complex 7 reacts with styrene with the rate constant 1.1 +/- 0.4 M-1 min(-1) at -70 degrees C to give epoxide and restore 1. Complex 8 is inert towards styrene at low temperature. The effect of donor ligand N-methylmorpholine-N-oxide (NMO) on the epoxidation of styrene by the system 1 + m-CPBA was studied. Addition of NMO (2-5 equiv.) to the solution of 1 in CH2Cl2 before interaction with m-CPBA was found to dramatically increase the rate of undesirable transformation of the reactive acylperoxo complex 7-NMO into relatively inert oxo complex-8-NMO. However, in the presence of styrene, such undesirable conversion is entirely suppressed by very rapid reaction of 8-NMO with styrene to afford styrene oxide and restore 1-NMO. (C) 2000 Elsevier Science B.V. All rights reserved.