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

In the presence of 1 equiv of BuNC, the homolytic cleavage of the Fe-H bond in the diiron terminal hydride complex [CpFe( t-H)(μ-η:η-bdt)FeCp][BF] (1[BF]) smoothly took place to release 1/2 H, followed by binding of a BuNC group to the unsaturated Fe center. Interestingly, upon exposure of 1[BF] 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[BF] with acetylene at 30 °C, two Fe-H bonds were broken, and then an acetylene molecule was coordinated to the diiron centers in a novel μ-η:η 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 FeFe to FeFe. These reaction patterns are reminiscent of the vital E state responsible for N binding and H 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[BF] with TMSN, the terminal hydride ligand was inserted into the azide group to give a diiron amide complex 4[BF] in moderate yield.