Interaction of a diiron thiolate-bridged complex, [Cp*Fe(μ-η(2):η(4)-bdt)FeCp*] (1) (Cp* = η(5)-C5Me5; bdt = benzene-1,2-dithiolate) with a proton gives an Fe(III)Fe(III) hydride bridged complex, [Cp*Fe(μ-bdt)(μ-H)FeCp*][BF4] (3[BF4]). According to in situ variable temperature (1)H NMR studies, the formation of 3[BF4] was evidenced to occur through a stepwise pathway: protonation occurring at an iron center to produce terminal hydride [Cp*Fe(μ-bdt)(t-H)FeCp*][BF4] (2) and subsequent intramolecular isomerization to bridging hydride 3[BF4]. A one-electron reduction of 3[BF4] by CoCp2 affords a paramagnetic mixed-valent Fe(II)Fe(III) hydride complex, [Cp*Fe(μ-η(2):η(2)-bdt)(μ-H)FeCp*] (4). Further, studies on protonation processes of diruthenium and iron-ruthenium analogues of 1, [Cp*M1(μ-bdt)M2Cp*] (M1 = M2 = Ru, 5; M1 = Fe, M2 = Ru, 8), provide experimental evidence for terminal hydride species at these bdt systems. Importantly, diiron or diruthenium hydride bridged complexes 3[BF4], 7[BF4] and iron-ruthenium heterodinuclear complex 8[PF6] can realize electrocatalytic hydrogen evolution.

By using 3,7‐dithianonane‐1,9‐dithiol (S4) and N,N′‐dimethyl‐N,N′‐bis(2‐mercaptoethyl)ethylenediamine (N2S2) as ligands, two CH3CN‐coordinated nickel‐iron heterodimetallic complexes, [NiS4Fe(CH3CN)Cp*][PF6] (1a) and [NiN2S2Fe(CH3CN)Cp*][PF6] (1b) (Cp* = η5‐C5Me5), were synthesized and characterized spectroscopically and crystallographically. Reactivities of 1a and 1b towards CO, CH2Cl2, HBF4, and NOPF6 have also been investigated. A series of complexes coordinated with small molecules [NiS4Fe(L)Cp*][PF6]n [n = 1, L = Cl (2a), CO (3a); n = 2, L = NO (4a)], [NiN2S2Fe(L)Cp*][PF6] [L = Cl (2b), CO (3b)] were obtained. We also studied the redox properties of 2a, 2b, 3a, and 3b by cyclic voltammetry in CH2Cl2 and in CH3CN solution. Complex 3a was found to be an excellent electrocatalyst for proton reduction from HBF4.

By employing S(CH 2 CH 2 S − ) 2 (tpdt) and O-(CH 2 CH 2 S − ) 2 (opdt) as bridging ligands, two nickel−iron and two nickel−ruthenium heterodimetallic complexes, [Cp*M(μ-1κ 3 SSS′:2κ 2 SS-tpdt)Ni(dppe)][PF 6 ] (1, M = Fe; 3, M = Ru) and [Cp*M(μ-1κ 3 SSO:2κ 2 SS-opdt)Ni(dppe)][PF 6 ] (2, M = Fe; 4, M = Ru) (Cp* = η 5 -C 5 Me 5 ; dppe = Ph 2 P(CH 2 ) 2 PPh 2), were obtained by a one-pot synthetic method and were identified by spectroscopy and X-ray crystallography. At 1 atm of CO, the pendant oxygen atom dissociated from the iron or ruthenium center and rapidly transferred to the nickel center when a CO molecule attacked the iron or ruthenium center in 2 and 4. However, there was no similar reaction occurring in 1 and 3 with the pendant sulfur atom. We confirmed the solid-state structure of the CO complex [Cp*Fe(t-CO)(μ-1κ 2 SS:2κ 3 SSO-opdt)Ni(dppe)][PF 6 ] (5), which represents a possible configuration in the CO-inhibited state of [NiFe]hydrogenase and exhibits no catalytic activity in electrochemical proton reduction.