Coinage Metal Effect on the Reduction of Carbon Dioxide with Monomeric Metal-Hydride Complexes

The role of the coinage metal in monomeric hydride complexes for the reduction of carbon dioxide to formate has been computationally addressed in this work. The common reaction mechanism, i. e. a concerted M-H (M=Cu, Ag, Au) bond attack to the CO2 carbon atom with one oxygen atom coordinating to the metal center, has been analyzed, revealing a kinetically less favorable reactivity for the gold-hydride complex. A thorough computational investigation discloses that, while all complexes feature covalent electron-sharing M-H bonds, copper- and silver-hydride complexes display a relevant M(delta+)-H(delta-) bond polarization, which enables an enhanced basicity of the hydride and, thereby, a more kinetically favorable CO2 reduction process. This study provides useful guidelines for the design of monomeric metal hydride complexes as promising candidates for the CO2 reduction.The reactivity of copper-, silver-, and gold-hydride complexes with carbon dioxide is significantly affected by the M-H bond polarity. The weak polarity of the Au-H bond decreases the basicity of the hydride, resulting in a less kinetically favorable CO2 reduction. image