Gutierrez Osvaldo, Tellis John C, Primer David N, Molander Gary A, Kozlowski Marisa C
Department of Chemistry, Roy and Diana Vagelos Laboratories, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
J Am Chem Soc. 2015 Apr 22;137(15):4896-9. doi: 10.1021/ja513079r. Epub 2015 Apr 8.
The cross-coupling of sp(3)-hybridized organoboron reagents via photoredox/nickel dual catalysis represents a new paradigm of reactivity for engaging alkylmetallic reagents in transition-metal-catalyzed processes. Reported here is an investigation into the mechanistic details of this important transformation using density functional theory. Calculations bring to light a new reaction pathway involving an alkylnickel(I) complex generated by addition of an alkyl radical to Ni(0) that is likely to operate simultaneously with the previously proposed mechanism. Analysis of the enantioselective variant of the transformation reveals an unexpected manifold for stereoinduction involving dynamic kinetic resolution (DKR) of a Ni(III) intermediate wherein the stereodetermining step is reductive elimination. Furthermore, calculations suggest that the DKR-based stereoinduction manifold may be responsible for stereoselectivity observed in numerous other stereoconvergent Ni-catalyzed cross-couplings and reductive couplings.
通过光氧化还原/镍双催化实现的sp(3)杂化有机硼试剂的交叉偶联，代表了在过渡金属催化过程中引入烷基金属试剂的一种新的反应模式。本文报道了一项使用密度泛函理论对这一重要转化的机理细节进行的研究。计算揭示了一条新的反应途径，该途径涉及通过烷基自由基加成到Ni(0)上生成的烷基镍(I)配合物，它可能与先前提出的机理同时起作用。对该转化的对映选择性变体的分析揭示了一种意外的立体诱导方式，涉及Ni(III)中间体的动态动力学拆分（DKR），其中立体决定步骤是还原消除。此外，计算表明基于DKR的立体诱导方式可能是许多其他立体汇聚的镍催化交叉偶联和还原偶联中观察到的立体选择性的原因。
