μ-Pyridine-bridged copper complex with robust proton-reducing ability

Abstract

The binuclear copper complex [Cu(DQPD)]₂ (where DQPD = deprotonated N²,N⁶-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH₂)) was synthesised and characterised by various spectroscopic as well as electrochemical techniques. The binuclear copper complex was converted into a mononuclear one by the addition of 2 equivalents of pTsOH into [Cu(DQPD)]₂. The interconversion between the dimer and monomer complex was studied through UV-Vis spectroscopy and cyclic voltammetry. The mononuclear copper complex showed high catalytic activity towards electrochemical proton reduction using acetic acid as the external proton source in 95 : 5 (v/v) DMF/H₂O. It showed an i_c/i_p (where i_c is the catalytic current in the presence of acetic acid and i_p is the reduction peak current in absence of acid) value of 24 and a turnover rate (TOF) of 111.70 s⁻¹ at a scan rate of 100 mV s⁻¹ at 25 °C. The [Cu(DQPD)]₂ complex evolved hydrogen under the irradiation of visible light in the presence of fluorescein (Fl) as a photosensitizer and triethylamine (TEA) as the sacrificial electron donor with an initial TOF of 0.03 s⁻¹ with respect to the catalyst.