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Mechanism of Asymmetric Hydrogenation of Ketones

酮的不对称氢化机理

基本信息

批准号：
15350079
负责人：
OHKUMA Takeshi
金额：
$ 8.77万
依托单位：
HOKKAIDO UNIVERSITY (2004)Nagoya University (2003)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

Chiral diphosphine/1,2-diamine Ru(II) complexes catalyze the rapid, productive, and enantioselective hydrogenation of simple ketones. The reaction proceeds smoothly even at an atmospheric pressure of H_2 at room temperature and is further accelerated by addition of an alkaline base or a strong organic base. Most importantly, the hydrogenation rate is initially increased to a great extent with an increase in base molarity, but subsequently decreases. Without a base, the rate is independent on H_2 pressure in the range of 1-16 atm, while in the presence of a base, the reaction is accelerated with increasing H_2 pressure. The extent of enantioselection is unaffected by hydrogen pressure, the presence or absence of base, the kind of base and coexisting metallic or organic cations, the nature of the solvent, or the substrate concentrations. The reaction with H_2/(CH_3)_2CHOH proceeds 50-times faster than that with D_2/(CD_3)_2CDOD in the absence of base, but the rate differs only by a facto … More r of 2 in the presence of KO-t-C_4H_9. These findings indicate that dual mechanisms are in operation, both of which are dependent on reaction conditions and involve heterolytic cleavage of H_2 to form a common reactive intermediate. The key [RuH(diphosphine)(diamine)]^+ and its solvate complex have been detected by ESI-TOFMS and NMR spectroscopy. The hydrogenation of ketones is proposed to occur via a nonclassical metal-ligand bifunctional mechanism involving a chiral RuH_2(diphosphine)(diamine), where a hydride on Ru and a proton of the NH_2 ligand are simultaneously transferred to the C=O function via a six-membered pericyclic transition state. The NH_2 unit in the diamine ligand plays a pivotal role in the catalysis. The reaction occurs in the outer coordination sphere of the 18e RuH_2 complex without C=O/metal interaction. The enantiofaces of prochiral aromatic ketones are kinetically differentiated on the molecular surface of the coordinatively saturated chiral RuH_2 intermediate rather than in a coordinatively unsaturated Ru template. Less

手性双膦/1，2-二胺Ru(II)络合物催化单酮的快速、高效和不对称氢化反应。在常温下，反应在常压下仍能顺利进行，加入碱性碱或强有机碱可进一步加速反应。最重要的是，随着碱摩尔比的增加，加氢速率最初有很大程度的提高，但随后又降低了。在无碱条件下，反应速率在1-16atm范围内与H_2压力无关，有碱存在时，随着H_2压力的增加，反应速度加快。对映体选择的程度不受氢气压力、碱的存在或不存在、碱的种类以及共存的金属或有机阳离子、溶剂的性质或底物浓度的影响。在无碱条件下，与H_2/(CH_3)_2CHOH的反应速度比与D_2/(CD_3)_2CDOD的反应速度快50倍，但仅相差…在KO-t-C_4H_9存在的情况下，r值大于2。这些结果表明存在双重反应机制，这两种机制都依赖于反应条件，都涉及H_2的异解裂解，形成共同的反应中间体。用ESI-TOFMS和核磁共振波谱鉴定了关键的[RuH(双膦)(二胺)]~+及其溶剂络合物。酮的氢化反应是通过一个手性RuH_2(双膦)(二胺)的非经典金属-配体双功能机理进行的，其中Ru上的氢化物和NH_2配体上的一个质子通过六元周环过渡态同时转移到C=O基团。二胺配体中的NH_2单元在催化反应中起着关键作用。反应发生在18E RuH_2络合物的外配位球内，没有C=O/金属相互作用。前手性芳香酮的对映体表面是在配位饱和的手性RuH_2中间体的分子表面上进行动力学区分的，而不是在配位不饱和的Ru模板上。较少