Hydride transfer between transition metal hydride complexes and carbon dioxide is a known reaction, where the thermodynamically favored direction of hydride transfer determines whether CO₂ reduction or formate oxidation occurs. Analysis of a growing database of thermodynamic parameters for transition metal hydride complexes now provides clear demarcation between metal hydrides which will function as oxidases and as reductases. The turning point is set at the hydricity of formate (44 kcal/mol in acetonitrile). Here, we utilize hydricity as a framework to reevaluate the catalytic activity and proposed mechanisms for formate oxidation and CO₂ reduction with several Ni and Rh P₂N₂ (P₂N₂ = 1,5-diaza-3,7-diphosphacyclooctane) complexes, respectively. The series of Ni P₂N₂ complexes have hydricities between 55–64 kcal/mol and are active catalysts for the electrochemical oxidation of formate. A surprising correlation of increased rate of electrochemical oxidation with decreased overpotential, η, is observed. The Rh P₂N₂ complexes have hydricities between 28–34 kcal/mol and function as hydrogenation catalysts for the reduction of CO₂ to formate. Learning from the reactivity of these catalysts, design principles for future metal hydride complexes are presented that focus on the ultimate goal of catalyst optimization for improved energy efficiency (overpotential) with high selectivity (Faradaic efficiency) for both formate oxidation and CO₂ reduction to formate.

中文翻译：

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过渡金属氢化物催化剂可实现CO ₂和甲酸酯的可持续相互转化：热力学和机理考虑

过渡金属氢化物络合物与二氧化碳之间的氢化物转移是已知的反应，其中热力学上有利于氢化物转移的方向决定了是否发生CO ₂还原或甲酸氧化。对过渡金属氢化物配合物不断增长的热力学参数数据库的分析现在提供了金属氢化物之间的明确分界，这些金属氢化物将起氧化酶和还原酶的作用。拐点设定为甲酸的水度（乙腈中为44 kcal / mol）。在这里，我们利用hydricity作为框架重新评估催化剂的活性和提出的机制为甲酸氧化和CO ₂还原与几个镍和Rh P ₂ Ñ ₂（P ₂ Ñ ₂＝ 1，5-二氮杂3，7-二磷环辛烷）配合物。Ni P ₂ N ₂系列配合物的水合度在55-64 kcal / mol之间，是甲酸的电化学氧化的活性催化剂。观察到电化学氧化速率增加与过电势η降低的惊人关联。Rh P ₂ N ₂络合物的水合度在28–34 kcal / mol之间，并充当氢化催化剂以还原CO ₂结成队。从这些催化剂的反应性中吸取教训，提出了未来金属氢化物配合物的设计原理，重点关注优化催化剂的最终目标，以提高甲酸甲酯氧化和将CO ₂还原成甲酸的能源（高电位）和高选择性（法拉第效率）。。