Fe 4 S 4 Cubane Type Cluster Immobilized on a Graphene Support: A High Performance H 2 Evolution Catalysis in Acidic Water.

The development of alternate catalysts that utilize non-precious metal based electrode materials such as the first row transition metal complexes is an important goal for economic fuel cell design. In this direction, a new Fe4 S4 cubane type cluster, [PPh4 ]2 [Fe4 S4 (DMET)4 ] (1) (DMET = cis-1,2-dicarbomethoxyethylene dithiolate) and its composite with functionalized graphene, (1@graphene) have been synthesized and characterized. The presence of nanocrystalline structures on graphene matrix in TEM and SEM images of 1@graphene indicate that the cluster (1) has been immobilized. The composite, 1@graphene evolves H2 gas from p-toluene sulfonic acid (TsOH) in a mixture of H2 O and CH3 CN under ambient conditions with a significant turnover number of 3200. 1@graphene electro-catalyzes H2 evolution at Ep , -1.2 V with remarkable throughput, catalytic efficiency and stability in only H2 O or in only CH3 CN. The Fe4 S4 cluster (1) alone electro-catalyzes hydrogen evolution at Ep , -0.75 V from TsOH in CH3 CN. The X-ray crystal structure of the Fe4 S4 cluster (1) (λmax , CH2 Cl2 , 823 nm; ε, 2200 mol-1 cm-1 ) shows that it is dianionic with a cumulative oxidation state of +2.5 for the iron centers and short C-S bond distances (ca., 1.712 Å & 1.727 Å) indicating the presence of sulfur based radicals.