The reaction of 2-pyridylamino-N,N-bis(2-methylene-4,6-difluorophenol) (H2L') and MoCl5 affords a molybdenum(VI) complex [MoL'(O)(2)] 1, a new molecular electrocatalyst, which has been determined by X-ray crystallography. Electrochemical studies show that a molybdenum(IV) intermediate is responsible for the reductive proton to generate H-2, and 1 can catalyze hydrogen evolution from acetic acid or aqueous buffer. Turnover frequency (TOF) reaches a maximum of 50.6 (in DMF) and 756 (in buffer, pH 6.0) moles of hydrogen per mole of catalyst per hour, respectively. Sustained proton reduction catalysis occurs at glassy carbon (GC) electrode to give H-2 over a 72 h electrolysis period and no observable decomposition of the catalyst. (C) 2014 Elsevier B.V. All rights reserved.