Hydroboration of carbonyl compounds is an important transformation in organic chemistry, and a growing interest in catalysis has focused on abundant and nontoxic base metals. Herein we describe an efficient salen manganese catalyst for the hydroboration of a broad range of carbonyl compounds with pinacolborane. The catalytic reactions proceeded rapidly (>99% conversion in <5 min) at room temperature with very low catalyst loadings. High turnover frequency (up to 5700 h^–1) was observed under these conditions. Several synthetically important functional groups were tolerated, and chemoselective hydroboration of aldehydes over ketones was achieved. The H/D kinetic isotopic effect of borane was determined to be 2.3. The Hammett correlation plot of a series of para-substituted acetophenone substrates, p-X-C₆H₆COCH₃ (X = H, Me, OMe, NO₂, Cl, Br, and CF₃) yielded a positive slope of ρ = +0.99. The crossover products were detected in the competition reaction of catecholborane and deuterated pinacolborane with acetophenone. The findings indicated a potential borane-mediated pathway that could account for the observation of the crossover products.

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锰催化剂对羰基的高选择性硼氢化反应：对反应机理的认识

羰基化合物的硼氢化反应是有机化学中的重要转变，对催化的兴趣日益浓厚，已集中在大量无毒的贱金属上。在本文中，我们描述了一种有效的塞伦锰催化剂，用于与频哪醇硼烷加氢硼化各种羰基化合物。在非常低的催化剂载量下，室温下催化反应迅速进行（在<5分钟内转化率> 99％）。在这些条件下，观察到高周转频率（长达5700 h ^–1）。耐受几个合成上重要的官能团，并且实现了醛在酮上的化学选择性氢硼化。硼烷的H / D动力学同位素效应确定为2.3。一系列的哈米特相关情节对取代的苯乙酮底物p -XC ₆ H ₆ COCH ₃（X = H，Me，OMe，NO ₂，Cl，Br和CF ₃）产生正斜率ρ= +0.99。在儿茶酚硼烷和氘代频哪硼烷与苯乙酮的竞争反应中检测到了交叉产物。研究结果表明潜在的硼烷介导的途径可能解释了交叉产物的观察。