Highly chemoselective palladium-catalyzed conjugate reduction of .alpha.,.beta.-unsaturated carbonyl compounds with silicon hydrides and zinc chloride cocatalyst
作者:Ehud. Keinan、Noam. Greenspoon
DOI:10.1021/ja00283a029
日期:1986.11
experiments and 'H NMR studies, a catalytic cycle is postulated in which the first step involves reversible coordination of the palladium complex to the electron-deficient olefin and oxidative addition of silicon hydride to form a hydridopalladium olefin complex. Migratory insertion of hydride into the coordinated olefin produces an intermediate palladium enolate which, via reductive elimination, collapses back
由可溶性钯催化剂、氢化硅烷和氯化锌组成的三组分体系能够有效地共轭还原α、不饱和酮和醛。最佳条件组包括二苯基硅烷作为最有效的氢化物供体,任何可溶于 0 或 I1 氧化态的钯配合物,当它被膦配体稳定时,以及作为最佳路易斯酸助催化剂的 ZnCl。该反应对于范围广泛的不饱和酮和醛非常普遍,并且对于这些迈克尔受体具有高度选择性,因为在这些条件下α,-不饱和羧酸衍生物的还原非常缓慢。当双氘代二苯基硅烷用于还原不饱和酮时,氘在底物的受阻较少的面上立体选择性地引入,并在 8 位上以区域选择性的方式引入。相反,当在痕量 D2O 存在下进行还原时,氘掺入发生在 a 位。在掺入氘的实验和 1 H NMR 研究的基础上,假定催化循环,其中第一步涉及钯配合物与缺电子烯烃的可逆配位和氢化硅的氧化加成以形成氢化钯烯烃配合物。氢化物迁移插入配位的烯烃产生中间体烯醇钯,通过还原消除,它塌缩回 Pd(0) 络合物和甲硅烷基烯
Highly Efficient Redox Isomerization of Allylic Alcohols and Transfer Hydrogenation of Ketones and Aldehydes Catalyzed by Ruthenium Complexes
作者:Pei Nian Liu、Kun Dong Ju、Chak Po Lau
DOI:10.1002/adsc.201000667
日期:2011.2.11
A dicationic dichloro-bipyridine-ruthenium complex shows very high catalytic activity in redox isomerization of allylic alcohols but a relatively low one in transferhydrogenation of ketones; surprisingly, the analogous dimethyl-bipyridine-ruthenium complex shows reverse catalytic activities in the two reactions.
Secondary phosphine oxides O=PHR2 (SPOs) were identified as multitalented preligands for the chemoselective Pd‐catalyzedoxidation of alcohols by a hydrogen‐abstracting methodology. SPOs were found to promote the hydrogen‐abstraction step as well as hydrogen transfer to a Michael acceptor by generating a putative active H−Pd species. The catalytic system operates under neutral conditions and was proven