Acidic ionic liquid/water solution as both medium and proton source for electrocatalytic H2 evolution by [Ni(P2N2)2]2+ complexes

The electrocatalytic reduction of protons to H-2 by [Ni((P2N2C6H4-hex)-N-Ph)(2)] (BF4)(2) ( where (P2N2C6H4-hex)-N-Ph = 1,5-di(4-n-hexylphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) in the highly acidic ionic liquid dibutylformamidium bis( trifluoromethanesulfonyl)amide shows a strong dependence on added water. A turnover frequency of 43,000-53,000 s(-1) has been measured for hydrogen production at 25 degrees C when the mole fraction of water (chi(H2O)) is 0.72. The same catalyst in acetonitrile with added dimethylformamidium trifluoromethanesulfonate and water has a turnover frequency of 720 s(-1). Thus, the use of an ionic liquid/aqueous solution enhances the observed catalytic rate by more than a factor of 50, compared to a similar acid in a traditional organic solvent. Complexes [Ni((P2N2C6H4X)-N-Ph)(2)] (BF4)(2) (X = H, OMe,CH2P(O)(OEt)(2),Br) are also catalysts in the ionic liquid/water mixture, and the observed catalytic rates correlate with the hydrophobicity of X.