Roberts Courtney C, Camasso Nicole M, Bowes Eric G, Sanford Melanie S
Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI, 48109, USA.
Department of Chemistry, University of British Columbia, Vancouver, British, Columbia, V6T 1Z1, Canada.
Angew Chem Int Ed Engl. 2019 Jul 1;58(27):9104-9108. doi: 10.1002/anie.201903638. Epub 2019 May 24.
Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp )-C and C(sp )-O bond-forming reactions at high-valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral Ni complex ligated by tris(pyrazolyl)borate and a cationic octahedral Ni complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp )-C(sp ) bond-forming reductive elimination occurs from both centers, but the Ni complex reacts up to 300-fold faster than the Ni , depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO ), the Ni complex exclusively undergoes C(sp )-OAc bond formation, while the Ni analogue forms the C(sp )-C(sp ) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M-C(sp ) bonds, and thus their relative reactivity towards outer-sphere S 2-type bond-forming reactions.
本文描述了对高价镍上影响C(sp³)-C和C(sp³)-O键形成反应的相对速率和选择性的因素进行的系统比较，该比较是作为氧化态的函数。比较了两种镍配合物：一种由三(吡唑基)硼酸盐配位的阳离子八面体镍配合物和一种由三(吡唑基)甲烷配位的阳离子八面体镍配合物。揭示了反应性/选择性的关键特征：1) 两个中心都发生C(sp³)-C(sp³)键形成的还原消除反应，但根据反应条件，镍(III)配合物的反应速度比镍(II)快300倍。相对反应性被认为源于配体解离动力学，其随氧化态以及可见光的存在与否而变化。2) 添加乙酸根(AcO⁻)后，镍(III)配合物仅发生C(sp³)-OAc键形成，而镍(II)类似物则选择性地形成C(sp³)-C(sp³)偶联产物。这种差异基于各自M-C(sp³)键的亲电性，以及它们对外层球S₂型键形成反应的相对反应性而得到合理解释。
