Experimental and Theoretical Study of CO2 Insertion into Ruthenium Hydride Complexes

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• 作者：Srinivasan Ramakrishnan ; Kate M. Waldie ; Ingolf Warnke ; Antonio G. De Crisci ; Victor S. Batista ; Robert M. Waymouth ; Christopher E. D. Chidsey
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：February 15, 2016
• 年：2016
• 卷：55
• 期：4
• 页码：1623-1632
• 全文大小：551K
• ISSN：1520-510X

文摘

The ruthenium hydride [RuH(CNN)(dppb)] (1; CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1,4-bis(diphenylphosphino)butane) reacts rapidly and irreversibly with CO₂ under ambient conditions to yield the corresponding Ru formate complex 2. In contrast, the Ru hydride 1 reacts with acetone reversibly to generate the Ru isopropoxide, with the reaction free energy ΔG°_298 K = −3.1 kcal/mol measured by ¹H NMR in tetrahydrofuran-d₈. Density functional theory (DFT), calibrated to the experimentally measured free energies of ketone insertion, was used to evaluate and compare the mechanism and energetics of insertion of acetone and CO₂ into the Ru–hydride bond of 1. The calculated reaction coordinate for acetone insertion involves a stepwise outer-sphere dihydrogen transfer to acetone via hydride transfer from the metal and proton transfer from the N–H group on the CNN ligand. In contrast, the lowest energy pathway calculated for CO₂ insertion proceeds by an initial Ru–H hydride transfer to CO₂ followed by rotation of the resulting N–H-stabilized formate to a Ru–O-bound formate. DFT calculations were used to evaluate the influence of the ancillary ligands on the thermodynamics of CO₂ insertion, revealing that increasing the π acidity of the ligand cis to the hydride ligand and increasing the σ basicity of the ligand trans to it decreases the free energy of CO₂ insertion, providing a strategy for the design of metal hydride systems capable of reversible, ergoneutral interconversion of CO₂ and formate.