Mechanism of catalytic cyclohydroamination by zirconium salicyloxazoline complexes.
Mechanism of catalytic cyclohydroamination by zirconium salicyloxazoline complexes.
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DOI：
10.1021/ja106588m
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发表时间：
2010-11
影响因子：
15
通讯作者：
Laura E. N. Allan;G. Clarkson;D. Fox;A. Gott;P. Scott
中科院分区：
文献类型：
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作者：
Laura E. N. Allan;G. Clarkson;D. Fox;A. Gott;P. Scott
通过动力学、化学计量和结构研究，探讨了Cp*LZr（NMe（2））（2）（L = κ（2）-水杨基恶唑啉）催化伯氨基烯烃氢胺化/环化反应的机理.对所研究的所有催化剂和氨基烯烃，发现速率定律为d[底物]/dt = k[催化剂]（1）[底物]（0）。五元环和六元环的生成速率基本相同，并有明显的KIE（k（H）/k（D）），表明N-H键断裂参与了一个非闭环的速率决定步骤（RDS）。值得注意的是，反应在THF中以与在甲苯中相同的速率进行，但是添加的不可环化的胺减慢了反应，表明虽然金属在RDS中不作为刘易斯酸，但涉及活化的底物。与其他催化剂相比，增加空间体积提高了速率，并通过X射线晶体学研究了其起源。从8个独立的动力学研究中提取的热力学参数表明，在决定速率的过渡态中，适度有序（ΔS（双匕首）= -13到23 cal/K·mol）和大量的整体键断裂（ΔH（双匕首）= 17到21 kcal/mol）。仲胺是非反应性的，因为是具有单个可胺解位点的催化剂，因此排除了酰胺基机理。提出了一种催化循环，包括反应性亚氨基物种的形成速率决定。化学计量步骤的过程中被证明是可行的，并通过合成和原位NMR光谱研究具有适当的速率。在不存在过量胺的情况下（在催化反应结束时）催化剂的命运是转化成由CH活化外围取代基产生的金属环物质。
The mechanism of hydroamination/cyclization of primary aminoalkenes by catalysts based on Cp*LZr(NMe(2))(2) (L = κ(2)-salicyloxazoline) is investigated in a range of kinetic, stoichiometric, and structural studies. The rate law is found to be d[substrate]/dt = k[catalyst](1)[substrate](0) for all catalysts and aminoalkenes studied. The overall rate is similar for formation of five- and six-membered rings, and a substantial KIE (k(H)/k(D)) is observed, indicating the involvement of N-H bond-breaking in a rate-determining step (RDS) which is not ring-closure. Remarkably, the reaction proceeds at the same rate in THF as it does in toluene, but added non-cyclizable amine slows the reaction, indicating that while the metal is not acting as a Lewis acid in the RDS, the activated substrate is involved. Also in contrast to other catalysts, increasing steric bulk improves the rate, and the origins of this are investigated by X-ray crystallography. Thermodynamic parameters extracted from eight independent kinetic studies indicate moderate ordering (ΔS(double dagger) = -13 to -23 cal/K·mol) and substantial overall bond disruption (ΔH(double dagger) = 17 to 21 kcal/mol) in the rate-determining transition state. Secondary amines are unreactive, as is a catalyst with a single aminolyzable site, thus excluding an amido mechanism. A catalytic cycle involving rate-determining formation of a reactive imido species is proposed. Stoichiometric steps in the process are shown to be feasible and have appropriate rates by synthetic and in situ NMR spectroscopic studies. The fate of the catalyst in the absence of excess amine (at the end of the catalytic reaction) is conversion to a metallacyclic species arising from CH activation of a peripheral substituent.