Enhancing Temperature Sensitivity of Redox Potential via Redox-Induced Change in Copper Coordination Number by an...

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 Cu^I 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 Cu^II and Cu^I centers, respectively. Variable-temperature electrochemical analysis reveals the temperature sensitivity of the apparent half-wave potential (E_1/2) of the Cu^II/Cu^I 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 Cu^II complex in MeCN solution. Similar analysis starting with the Cu^I complex affords α = 2.6(2) mV °C^-1 in the presence of ^tBu-py, providing a record-high temperature sensitivity of E_1/2 of the Cu^II/Cu^I couple in MeCN solution.