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首页> 外文期刊>Catalysis science & technology >DFT study of CO2 hydrogenation catalyzed by a cobalt-based system: an unexpected formate anion-assisted deprotonation mechanism
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DFT study of CO2 hydrogenation catalyzed by a cobalt-based system: an unexpected formate anion-assisted deprotonation mechanism

机译：DFT二氧化碳加氢催化的研究钴基系统:一个意想不到的甲酸anion-assisted去质子化机制

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Catalyzed hydrogenation of CO2 by earth-abundant metal complexes is a promising strategy to utilize hydrogen as a kind of sustainable energy and to reduce greenhouse gases. A systematic density functional theory (DFT) study is presented for CO2 hydrogenation catalyzed by the Co.dmpe)(2)H (dmpe: 1,2-bis.dimethylphosphino)-ethane) complex with Verkade's base as an additive. An unexpected formate anion-assisted deprotonation mechanism is unfolded, which is different from the generally accepted additive base-catalyzed deprotonation mechanism. The complete catalytic cycle involves three main steps: (i) oxidative addition, (ii) deprotonation of the dihydride complex, and (iii) hydrogenation of CO2. The cobalt monohydride complex Co(dmpe)(2)H is found to be the catalytically active species and the rate-determining step is the hydrogenation of CO2 (Delta G double dagger = 20.9 kcal mol(-1)). Furthermore, the hydride transfer process prefers the reductive elimination mechanism (Delta G double dagger = 20.9 kcal mol(-1)) to the direct transfer mechanism (Delta G double dagger = 23.3 kcal mol(-1)). In contrast, the cobalt dihydride complex [Co(dmpe)(2)H-2](+) is less likely to be the active species, which should be deprotonated to the cobalt monohydride species for further hydrogenation. The deprotonation of cobalt dihydride to cobalt monohydride is found to be promoted by the formate anion (Delta G double dagger = 10.5 kcal mol(-1)) instead of Verkade's base (Delta G double dagger = 36.9 kcal mol(-1)). On the other hand, a direct heterolytic cleavage of H-2 assisted by the base to cobalt monohydride is less feasible compared with the oxidative addition of H-2. These results can well explain the necessity for oxidative addition and the appearance of formic acid after Verkade's base has run out in the experiments, and are in good agreement with the experimental observation that the hydrogenation of CO2 instead of the deprotonation is the rate-determining step. The present results provide sharp insights and helpful guidelines for designing novel hydrogenation systems with transition metal complexes and bases.
机译：地球上充足的催化加氢的二氧化碳金属配合物是一种很有前途的战略利用氢作为一种可持续的能源和减少温室气体排放。密度泛函理论(DFT)的研究提出了二氧化碳加氢催化的Co.dmpe) (2) H(并给出:1, 2-bis.dimethylphosphino)乙烷)复杂Verkade作为添加剂的基础。甲酸anion-assisted去质子化机制展开,这是不同于一般接受添加剂base-catalyzed去质子化机制。三个主要步骤:(i)氧化,(2)去质子化的二氢化物复杂,(3)二氧化碳加氢。复杂的公司(并)(2)H是发现的物种和催化地活跃的加氢速率决定步骤是二氧化碳(δG双匕首= 20.9千卡摩尔(1))。此外,更喜欢氢化物转移过程还原消除机制(δG双匕首= 20.9千卡摩尔(1))来的直接传输机制(δG双匕首= 23.3千卡摩尔(1))。复杂的(有限公司(并)(2)2)(+)不太可能活跃的物种,这应该deprotonated为进一步monohydride钴物种加氢。二氢化物钴monohydride发现甲酸盐阴离子(δG双提升匕首= 10.5千卡摩尔(1))而不是Verkade基地(δG双匕首= 36.9千卡摩尔(1))。另一方面,一个直接的异种溶解的乳沟2协助的钴monohydride基地与氧化相比不太可行吗添加2。氧化的必要性和甲酸在Verkade基地实验已经耗尽了,,好吗协议的实验观察加氢的二氧化碳而不是去质子化速率决定步骤。目前提供敏锐的洞察力和结果有用的指导方针,设计新颖与过渡金属氢化系统设施和基地。

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