New insights into solvolysis and reorganization energy from gas-phase, electrochemical, and theoretical studies of Oxo-Tp Mo^v molecules

Molecules of the general form Tp^*MoO(OR)₂ [where Tp^* = hydrotris(3,5-dimethyl-1 -pyrazolyl)borate and (OR)₂ = (OMe)₂, (OEt)₂, and (O ⁿPr)₂ for alkoxide ligands and (OR)₂ = O(CH₂)₃O, O(CH₂)₄O, and O[CH(CH ₃)CH₂CH(CH₃)P for diolato ligands] were studied using gas-phase photoelectron spectroscopy, cyclic voltammetry, and density functional theory (DFT) calculations to examine the effect of increasing ligand size and structure on the oxomolybdenum core. Oxidation potentials and first ionization energies are shown to be sensitive to the character of the diolato and alkoxide ligands. A linear correlation between the solution-phase oxidation potentials and the gas-phase ionization energies resulted in an unexpected slope of greater than unity. DFT calculations indicated that this unique example of a system in which oxidation potentials are more sensitive to substitution than vertical ionization energies is due to the large differences in the cation reorganization energies, which range from 0.2 eV or less for the molecules with diolato ligands to around 0.5 eV for the molecules with alkoxide ligands.