Synthesis and Electrocatalytic Property of Diiron Hydride Complexes Derived from a Thiolate-Bridged Diiron Complex

Interaction of a diiron thiolate-bridged complex, [Cp*Fe­(μ-η2:η4-bdt)­FeCp*] (1) (Cp* = η5-C5Me5; bdt = benzene-1,2-dithiolate) with a proton gives an FeIIIFeIII hydride bridged complex, [Cp*Fe­(μ-bdt)­(μ-H)­FeCp*]­[BF4] (3­[BF4]). According to in situ variable temperature 1H 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 FeIIFeIII hydride complex, [Cp*Fe­(μ-η2:η2-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.