Nickel-catalyzed cross-coupling of unactivated alkyl halides using bis(pinacolato)diboron as reductant
作者:Hailiang Xu、Chenglong Zhao、Qun Qian、Wei Deng、Hegui Gong
DOI:10.1039/c3sc51098k
日期:——
The use of bis(pinacolato)diboron as the terminal reductant allows the efficient Ni-catalyzed coupling of unactivated secondary and primary alkyl halides, generating the C(sp3)–C(sp3) coupling products in good yields. The mild catalytic conditions display excellent functional group tolerance, and good chemoselectivities which require only 1.5 equiv. of primary bromides for the coupling with secondary bromides. Preliminary mechanistic studies suggest that an in situ organoborane/Suzuki process is not likely. It was identified that the base and ligand have more profound impact on selecting this reductive coupling pathway. The good chemoselectivity appears to be evoked by the formation of Ni–Bpin catalytic intermediates, which demands matched sizes and reactivities of the alkyl halide coupling partners for optimal coupling efficiency.
使用双(匹卡洛酸酯)二硼作为末端还原剂,可以高效催化非活化的次级和一级卤烃进行镍催化偶联反应,生成良产率的C(sp3)–C(sp3)偶联产物。这种温和的催化条件表现出优异的官能团耐受性,以及良好的化学选择性,仅需1.5当量的一级溴化物与次级溴化物进行偶联。初步的机理研究表明,体内有机硼/铃木反应的可能性不大。研究发现,碱和配体对选择这一还原偶联路径有更深远的影响。良好的化学选择性似乎是由于Ni–Bpin催化中间体的形成,这要求卤烃偶联伙伴之间的尺寸和反应性匹配,以实现最佳偶联效率。