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*] (<b>1</b>) (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] (<b>3­[BF</b>_<b>4</b><b>]</b>). According to <i>in situ</i> variable temperature ¹H NMR studies, the formation of <b>3­[BF</b>_<b>4</b><b>]</b> was evidenced to occur through a stepwise pathway: protonation occurring at an iron center to produce terminal hydride [Cp*Fe­(μ-bdt)­(<i>t</i>-H)­FeCp*]­[BF₄] (<b>2</b>) and subsequent intramolecular isomerization to bridging hydride <b>3­[BF</b>_<b>4</b><b>]</b>. A one-electron reduction of <b>3­[BF</b>_<b>4</b><b>]</b> by CoCp₂ affords a paramagnetic mixed-valent Fe^IIFe^III hydride complex, [Cp*Fe­(μ-η²:η²-bdt)­(μ-H)­FeCp*] (<b>4</b>). Further, studies on protonation processes of diruthenium and iron–ruthenium analogues of <b>1</b>, [Cp*M1­(μ-bdt)­M2Cp*] (M1 = M2 = Ru, <b>5</b>; M1 = Fe, M2 = Ru, <b>8</b>), provide experimental evidence for terminal hydride species at these bdt systems. Importantly, diiron or diruthenium hydride bridged complexes <b>3­[BF</b>_<b>4</b><b>]</b>, <b>7­[BF</b>_<b>4</b><b>]</b> and iron–ruthenium heterodinuclear complex <b>8­[PF</b>_<b>6</b><b>]</b> can realize electrocatalytic hydrogen evolution