We report a new design strategy for enhancing the temperature sensitivity of molecular redox potentials that is based on a redox-induced change in the metal coordination number facilitated by an external ligand. The Cu complex bis(2,9-dimethyl-1,10-phenanthroline)copper(II) binds coordinating ligands, including MeCN, whereas the CuI analog remains tetracoordinate. Upon introduction of a stronger donor, 4-tert-butylpyridine (tBu-py), the MeCN ligand is displaced while retaining penta- and tetracoordination at the CuII and CuI centers, respectively. Variable-temperature electrochemical analysis reveals the temperature sensitivity of the apparent half-wave potential (E1/2) of the CuII/CuI couple to increase from α = 1.70(6) mV °C-1 to α = 2.3(2) mV °C-1 upon addition of 15.0 equiv of tBu-py to the MeCN-bound CuII complex in MeCN solution. Similar analysis starting with the CuI complex affords α = 2.6(2) mV °C-1 in the presence of tBu-py, providing a record-high temperature sensitivity of E1/2 of the CuII/CuI couple in MeCN solution.
Carmona-Pérez et al. (Tue,) studied this question.