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 Fe^IIIFe^III 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 Fe^IIFe^III 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.