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

In the presence of 1 equiv of (BuNC)-Bu-t, the homolytic cleavage of the Fe-III-H bond in the diiron terminal hydride complex [Cp*Fe(t-H)(mu-eta(2):eta(4)-bdt)FeCp*] [BF4] (1[BF4]) smoothly took place to release 1/2 H-2, followed by binding of a (BuNC)-Bu-t 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 degrees C, two Fe-III-H bonds were broken, and then an acetylene molecule was coordinated to the diiron centers in a novel mu-eta(2):eta 2 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 (FeFeIII)-Fe-III to (FeFeII)-Fe-III. These reaction patterns are reminiscent of the vital E-4 state responsible for N-2 binding and H-2 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.