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 Fe(4)S(4) cubane type cluster, [PPh(4)](2)[Fe(4)S(4)(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 H(2) gas from p-toluene sulfonic acid (TsOH) in a mixture of H(2)O and CH(3)CN under ambient conditions with a significant turnover number of 3200. 1@graphene electro-catalyzes H(2) evolution at E(p), −1.2 V with remarkable throughput, catalytic efficiency and stability in only H(2)O or in only CH(3)CN. The Fe(4)S(4) cluster (1) alone electro-catalyzes hydrogen evolution at E(p), −0.75 V from TsOH in CH(3)CN. The X-ray crystal structure of the Fe(4)S(4) cluster (1) (λ(max), CH(2)Cl(2), 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.