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

In the presence of 1 equiv of tBuNC, the homolytic cleavage of the FeIII-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 FeII 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 FeIII-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 FeIIIFeIII to FeIIIFeII. 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.