Reactivity toward Unsaturated Small Molecules of Thiolate-Bridged Diiron Hydride Complexes

In the presence of 1 equiv of ^tBuNC, the homolytic cleavage of the Fe^III-H bond in the diiron terminal hydride complex [Cp*Fe( t-H)(μ-η²:η⁴-bdt)FeCp*][BF₄] (1[BF₄]) smoothly took place to release 1/2 H₂, followed by binding of a ^tBuNC group to the unsaturated Fe^II center. Interestingly, upon exposure of 1[BF₄] to 1 atm of acetylene, the isomerization process of the hydride ligand from the terminal to bridging coordination site was unaffected. Upon treatment of the diiron hydride bridged complex 2[BF₄] with acetylene at 30 °C, two Fe^III-H bonds were broken, and then an acetylene molecule was coordinated to the diiron centers in a novel μ-η²:η² side-on fashion. In the above reaction system, the hydride ligands whether terminal or bridging all play a role as the electron donor for the reduction of the diiron centers from Fe^IIIFe^III to Fe^IIIFe^II. These reaction patterns are reminiscent of the vital E₄ state responsible for N₂ binding and H₂ liberation in the catalytic cycle of nitrogenase, which contains two {Fe-H-Fe} motifs as electron reservoirs for the reduction of the iron centers. Differently, when treating 1[BF₄] with TMSN₃, the terminal hydride ligand was inserted into the azide group to give a diiron amide complex 4[BF₄] in moderate yield.