We investigate the mechanism of primary alkane CH bond activation with dioxo-dicopper ([Cu₂O₂]²⁺) complexes, which serve as model catalysts for enzymes capable of activating CH bonds under mild conditions. As large H/D kinetic isotope effects (KIEs) are observed in enzymes and their synthetic mimics, we employ density functional theory along with variational transition-state theory with multidimensional tunneling to estimate reaction rate coefficients. By systematically varying ligand electrophilicity and substrate chain length, we examine trends in rate coefficients and kinetic isotope effects for the two proposed CH activation pathways – one-step oxo-insertion and two-step radical recombination. Although larger tunneling transmission coefficients are obtained for the radical pathway, the oxo-insertion mechanism yields higher rate coefficients on account of lower activation barriers. The question of the preferred CH activation mechanism, however, remains open: excellent agreement is observed between the predicted and known experimental KIE results for the radical pathway, while calculated Hammett slopes for the oxo-insertion pathway closely mirror experiments.

中文翻译：

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[Cu2O2]2+ 复合物活化 CH 中的量子效应


我们研究了二氧代-二铜 （[Cu₂O₂] ²⁺） 配合物激活伯烷 CH 键的机制，二氧代-二铜配合物作为能够在温和条件下激活 CH 键的酶的模型催化剂。由于在酶及其合成模拟物中观察到较大的 H/D 动力学同位素效应 （KIEs），我们采用密度泛函理论以及具有多维隧穿的变分过渡态理论来估计反应速率系数。通过系统地改变配体亲电性和底物链长度，我们检查了两种拟议的 CH 激活途径（一步氧基插入和两步自由基复合）的速率系数和动力学同位素效应的趋势。尽管自由基途径获得了更大的隧穿传输系数，但由于激活屏障较低，羰基插入机制产生了更高的速率系数。然而，首选 CH 激活机制的问题仍然悬而未决：在自由基途径的预测和已知实验 KIE 结果之间观察到极好的一致性，而羰基插入途径的计算 Hammett 斜率与实验非常相似。