Bryliakov Konstantin P, Talsi Evgenii P
G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation.
Inorg Chem. 2003 Nov 3;42(22):7258-65. doi: 10.1021/ic034578w.
Intermediates of chromium-salen catalyzed alkene epoxidations were studied in situ by EPR, (1)H and (2)H NMR, and UV-vis/NIR spectroscopy (where chromium-salens were (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (1) and racemic N,N'-bis(3,4,5,6-tetra-deuterosalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (2)). High-valence chromium complexes, intermediates of epoxidation reactions, were detected and characterized by EPR and NMR. They are the reactive mononuclear oxochromium(V) intermediate (A) Cr(V)O(salen)L (where L = Cl(-) or a solvent molecule) and an inactive chromium-salen binuclear complex (B) which acts as a reservoir of the active species. The latter complex demonstrates an EPR signal characteristic of oxochromium(V)-salen species and (1)H NMR spectra typical for chromium(III)-salen complexes, and it is identified as mixed-valence binuclear L(1)(salen)Cr(III)OCr(V)(salen)L(2) (L(1), L(2) = Cl(-) or solvent molecules). The intermediates Cr(V)O(salen)L and L(1)(salen)Cr(III)OCr(V)(salen)L(2) exist in equilibrium, and their ratio can be affected by addition of donor ligands (DMSO, DMF, H(2)O, pyridine). Addition of donor additives increases the fraction of A over that of B. The same two complexes can be obtained with m-CPBA as oxidant. Reactivities of the Cr(V)O(salen)L complexes toward E-beta-methylstyrene were measured in DMF. The L(1)(salen)Cr(III)OCr(V)(salen)L(2) intermediate has been proposed to be a reservoir of the true reactive chromium(V) species. The chromium-salen catalysts demonstrate low turnover numbers (ca. 5), probably due to ligand degradation processes.
通过电子顺磁共振（EPR）、氢核磁共振（¹H NMR）和氘核磁共振（²H NMR）以及紫外可见/近红外光谱（其中铬-萨伦配合物为（S,S）-(+)-N,N'-双（3,5-二叔丁基水杨醛）-1,2-环己二胺氯化铬（III）（1）和外消旋N,N'-双（3,4,5,6-四氘代水杨醛）-1,2-环己二胺氯化铬（III）（2））对铬-萨伦催化的烯烃环氧化反应中间体进行了原位研究。通过EPR和NMR检测并表征了作为环氧化反应中间体的高价铬配合物。它们是活性单核氧铬（V）中间体（A）Cr（V）O（萨伦）L（其中L = Cl⁻或溶剂分子）和作为活性物种储存库的无活性铬-萨伦双核配合物（B）。后一种配合物表现出氧铬（V）-萨伦物种的特征EPR信号和铬（III）-萨伦配合物典型的¹H NMR光谱，并且被鉴定为混合价双核L₁（萨伦）Cr（III）OCr（V）（萨伦）L₂（L₁、L₂ = Cl⁻或溶剂分子）。中间体Cr（V）O（萨伦）L和L₁（萨伦）Cr（III）OCr（V）（萨伦）L₂处于平衡状态，它们的比例会受到供体配体（二甲基亚砜、二甲基甲酰胺、水、吡啶）添加的影响。供体添加剂的添加会增加A相对于B的比例。以间氯过氧苯甲酸（m-CPBA）作为氧化剂时也能得到相同的两种配合物。在二甲基甲酰胺中测量了Cr（V）O（萨伦）L配合物对E-β-甲基苯乙烯的反应活性。已提出L₁（萨伦）Cr（III）OCr（V）（萨伦）L₂中间体是真正活性铬（V）物种的储存库。铬-萨伦催化剂表现出较低的周转数（约为5），这可能是由于配体降解过程所致。
