Haynes M Taylor, Liu Peng, Baxter Ryan D, Nett Alex J, Houk K N, Montgomery John
Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109-1055, United States.
J Am Chem Soc. 2014 Dec 17;136(50):17495-504. doi: 10.1021/ja508909u. Epub 2014 Dec 3.
The mechanism of nickel(0)-catalyzed reductive coupling of aldehydes and alkynes has been studied. Extensive double-labeling crossover studies have been conducted. While previous studies illustrated that phosphine- and N-heterocyclic carbene-derived catalysts exhibited differing behavior, the origin of these effects has now been evaluated in detail. Many variables, including ligand class, sterics of the ligand and alkyne, temperature, and ring size being formed in intramolecular versions, all influence the extent of crossover observed. A computational evaluation of these effects suggests that dimerization of a key metallacyclic intermediate provides the origin of crossover. Protocols that proceed with crossover are typically less efficient than those without crossover given the thermodynamic stability and low reactivity of the dimeric metallacycles involved in crossover pathways.
对零价镍催化的醛与炔烃的还原偶联机理进行了研究。开展了广泛的双标记交叉实验。虽然之前的研究表明，膦和氮杂环卡宾衍生的催化剂表现出不同的行为，但现在已对这些效应的起源进行了详细评估。许多变量，包括配体种类、配体和炔烃的空间位阻、温度以及分子内反应中形成的环大小，都会影响观察到的交叉程度。对这些效应的计算评估表明，关键金属环中间体的二聚作用是交叉现象的起源。考虑到交叉途径中涉及的二聚金属环的热力学稳定性和低反应活性，有交叉现象的反应方案通常不如无交叉现象的方案高效。
