Reduction of Systematic Uncertainty in DFT Redox Potentials of Transition-Metal Complexes

Reliable calculations of redox potentials could provide valuable insight into catalytic mechanisms of electrochemically active transition-metal complexes as well as guidelines for the design of new electrocatalysts. However, the correlation between theoretical and experimental data is often uncertain, since redox properties depend strongly on experimental conditions of electrochemical measurements, including the nature of the solvent, electrolyte, and working electrode. Here, we show that the use of internal references allows for quantitative theoretical predictions of redox potentials with standard deviations σ comparable to typical experimental errors of cyclic voltammetry measurements. Agreement for first-, second-, and third-row transition-metal complexes is demonstrated even at a rather modest level of density functional theory (σ = 64 mV for the UB3LYP/6-311G* level). This is shown for a series of benchmark redox couples, including ([MCp₂]^0/+ (Cp = η⁵-cyclopentadienyl), [MCp*₂]^0/+ (Cp* = η⁵-1,2,3,4,5-pentamethylcyclopentadienyl), [M­(bpy)₃]^2+/3+ (bpy =2,2′-bipyridine), and [Ir­(acac)₃]^0/+ (acac = acetylacetonate), with M = Fe, Co, Ni, Ru, Os, or Ir) in various nonaqueous solvents [acetonitrile (MeCN), dimethyl sulfoxide (DMSO), and dichloromethane (DCM)]

Organometallic Ni Pincer Complexes for the Electrocatalytic Production of Hydrogen

Nonplatinum metals are needed to perform cost-effective water reduction electrocatalysis to enable technological implementation of a proposed hydrogen economy. We describe electrocatalytic proton reduction and H₂ production by two organometallic nickel complexes with tridentate pincer ligands. The kinetics of H₂ production from voltammetry is consistent with an overall third order rate law: the reaction is second order in acid and first order in catalyst. Hydrogen production with 90–95% Faradaic yields was confirmed by gas analysis, and UV–vis spectroscopy suggests that the ligand remains bound to the catalyst over the course of the reaction. A computational study provides mechanistic insights into the proposed catalytic cycle. Furthermore, two proposed intermediates in the proton reduction cycle were isolated in a representative system and show a catalytic response akin to the parent compound

Organometallic Ni Pincer Complexes for the Electrocatalytic Production of Hydrogen

Nonplatinum metals are needed to perform cost-effective water reduction electrocatalysis to enable technological implementation of a proposed hydrogen economy. We describe electrocatalytic proton reduction and H₂ production by two organometallic nickel complexes with tridentate pincer ligands. The kinetics of H₂ production from voltammetry is consistent with an overall third order rate law: the reaction is second order in acid and first order in catalyst. Hydrogen production with 90–95% Faradaic yields was confirmed by gas analysis, and UV–vis spectroscopy suggests that the ligand remains bound to the catalyst over the course of the reaction. A computational study provides mechanistic insights into the proposed catalytic cycle. Furthermore, two proposed intermediates in the proton reduction cycle were isolated in a representative system and show a catalytic response akin to the parent compound