Heteropolymetallic [FeFe]-hydrogenase mimics: synthesis and electrochemical properties

Abstract

The synthesis and electrochemical properties of tetranuclear[Fe2S2]-hydrogenase mimic species containing Pt(II), Ni(II), and Ru(II)complexes have been studied. To this end, a new tetranuclear [Fe2S2] complexcontaining a 5,5′- diisocyanide-2,2′-bipyridine bridging ligand has been designedand coordinated to the metal complexes through the bipyridine moiety. Thus, thetetranuclear [Fe2S2] complex (6) coordinates to Pt(II), Ni(II) and Ru(II) yieldingthe corresponding metal complexes. The new metal center in the bipyridine linkermodulates the electronic communication between the redox-active [Fe2S2] units. Thus, electrochemical studies and DFT calculations have shown that the presenceof metal complexes in the structure strongly affect the electronic communicationbetween the [Fe2S2] centers. In the case of diphosphine platinum compounds 10,the structure of the phosphine ligand plays a crucial role to facilitate or to hinderthe electronic communication between [Fe2S2] moieties. Compound 10a, bearing a dppe ligand, shows weak electroniccommunication (ΔE = 170 mV), whereas the interaction is much weaker in the Pt-dppp derivative 10b (ΔE = 80 mV) and virtuallynegligible in the Pt-dppf complex 10c. The electronic communication is facilitated by incorporation of a Ru-bis(bipyridine) complex,as observed in the BF4 salt 12 (ΔE = 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 theredox-active centers, which, in turn, can be modulated by a transition metal.