Synthesis, protonation and electrochemical properties of trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, Ph) with an internal pendant nitrogen base as a proton relay

Two trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1; Ph, 2) containing an internal base were prepared as biomimetic models for the active sites of FeFe and NiFe hydrogenases. Treatment of complex Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2N(n-Bu)] (1) with HOTf gave an N-protonated complex [Fe2(CO)6(μ3-S)2{Ni(Ph2PCH2)2NH(n-Bu)}][OTf] ([1H][OTf]). The structures of complexes 1, 2 and [1H][OTf] were determined by X-ray crystallography, which shows that the proton held by the N atom of [1H][OTf] lies in an equatorial position. Cyclic voltammograms of complexes 1 and [1H][OTf] were studied and compared with that of Fe2(CO)6(μ3-S)2[Ni(dppe)].