Calculation of thermodynamic hydricities and the design of hydride donors for CO ₂ reduction

Abstract

We have developed a correlation between experimental and density functional theory-derived results of the hydride-donating power, or “hydricity”, of various ruthenium, rhenium, and organic hydride donors. This approach utilizes the correlation between experimental hydricity values and their corresponding calculated free-energy differences between the hydride donors and their conjugate acceptors in acetonitrile, and leads to an extrapolated value of the absolute free energy of the hydride ion without the necessity to calculate it directly. We then use this correlation to predict, from density functional theory-calculated data, hydricity values of ruthenium and rhenium complexes that incorporate the pbnHH ligand—pbnHH = 1,5-dihydro-2-(2-pyridyl)-benzo[ b ]-1,5-naphthyridine—to model the function of NADPH. These visible light-generated, photocatalytic complexes produced by disproportionation of a protonated-photoreduced dimer of a metal-pbn complex may be valuable for use in reducing CO 2 to fuels such as methanol. The excited-state lifetime of photoexcited [Ru(bpy) 2 (pbnHH)] 2+ is found to be about 70 ns, and this excited state can be reductively quenched by triethylamine or 1,4-diazabicyclo[2.2.2]octane to produce the one-electron-reduced [Ru(bpy) 2 (pbnHH)] + species with half-life exceeding 50 μs, thus opening the door to new opportunities for hydride-transfer reactions leading to CO 2 reduction by producing a species with much increased hydricity.

Predicting the reactivity of hydride donors in water: thermodynamic constants for hydrogen

“…5,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] While the thermodynamic constants for H 2 in some organic solvents (such as those in dimethylsulfoxide and acetonitrile) 5 have been used with reasonable consistency, a common set of values for the analogous thermodynamic constants in water has not yet been adopted. 5,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] While the thermodynamic constants for H 2 in some organic solvents (such as those in dimethylsulfoxide and acetonitrile) 5 have been used with reasonable consistency, a common set of values for the analogous thermodynamic constants in water has not yet been adopted.…”

Hydrogenative Carbon Dioxide Reduction Catalyzed by Mononuclear Ruthenium Polypyridyl Complexes: Discerning between Electronic and Steric Effects

“…The anionic bid -ligand has a high capacity for sigma donation of electron density to the metal center, producing initial complexes that have high thermodynamic hydricity (low GºH-) [42][43][44][45] and thus react readily with CO2, so that this step is not turnover limiting. Instead, the H-H cleavage step with its associated G2°, ‡ is turnover limiting.…”

Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H]+: Experimental and Computational Studies of their Hydricities, Interaction with CO2, and Photochemistry

“…[5,6] It is of interest to measure the thermodynamic hydricities of N-trans- [6b] Therelatively weak ground-state hydricity of N-trans-[1-H] + explains its stability and lack of reactivity towards CO 2 in the ground state.E fforts were also made to determine the ground-state hydricity of C-trans-[1-H] + .W ee ncountered difficulty in measuring the heat of reaction of C-trans-[1-H] + with tris(pmethoxyphenyl)trityl or TEMPO + owing to the instability of the hydride. [5,6] It is of interest to measure the thermodynamic hydricities of N-trans- [6b] Therelatively weak ground-state hydricity of N-trans-[1-H] + explains its stability and lack of reactivity towards CO 2 in the ground state.E fforts were also made to determine the ground-state hydricity of C-trans-[1-H] + .W ee ncountered difficulty in measuring the heat of reaction of C-trans-[1-H] + with tris(pmethoxyphenyl)trityl or TEMPO + owing to the instability of the hydride.…”