Heteropolymetallic [FeFe]-Hydrogenase Mimics: Synthesis and Electrochemical Properties.

The synthesis and electrochemical properties of tetranuclear [Fe 2 S 2 ]-hydrogenase mimic species containing Pt(II), Ni(II), and Ru(II) complexes have been studied. To this end, a new tetranuclear [Fe 2 S 2 ] complex containing a 5,5'-diisocyanide-2,2'-bipyridine bridging ligand has been designed and coordinated to the metal complexes through the bipyridine moiety. Thus, the tetranuclear [Fe 2 S 2 ] complex ( 6 ) coordinates to Pt(II), Ni(II) and Ru(II) yielding the corresponding metal complexes. The new metal center in the bipyridine linker modulates the electronic communication between the redox-active [Fe 2 S 2 ] units. Thus, electrochemical studies and DFT calculations have shown that the presence of metal complexes in the structure strongly affect the electronic communication between the [Fe 2 S 2 ] centers. In the case of diphosphine platinum compounds 10 , the structure of the phosphine ligand plays a crucial role to facilitate or to hinder the electronic communication between [Fe 2 S 2 ] moieties. Compound 10a , bearing a dppe ligand, shows weak electronic communication (Δ E = 170 mV), whereas the interaction is much weaker in the Pt-dppp derivative 10b (Δ E = 80 mV) and virtually negligible in the Pt-dppf complex 10c . The electronic communication is facilitated by incorporation of a Ru-bis(bipyridine) complex, as observed in the BF 4 salt 12 (Δ E = 210 mV) although the reduction of the [FeFe] centers occurs at more negative potentials. Overall, the experimental-computational procedure used in this work allows us to study the electronic interaction between the redox-active centers, which, in turn, can be modulated by a transition metal.