Ligand Effects On The Electrochemical Behavior Of [Fe-2(Co)(5)(L){Mu-(Sch2)(2)(Ph)P=O}] (L = Pph3, P(Oet)(3)) Hydrogenase Model Complexes

In this paper we study the influence of substituting one CO ligand in [Fe-2(CO)(6){mu-(SCH2)(2)(Ph)P=O}] (1) by better s-donor L ligands affording [Fe-2(CO)(5)(L){mu-(SCH2)(2)(Ph)P=O}] {L = PPh3 (2) and P(OEt)(3) (3)} in relation to the steric interactions and the voltammetric behavior. Cyclic voltammetric investigations under N-2 and CO showed remarkable differences in the electrochemical behaviour of complexes 2 and 3: (i) Complex 2 tends to expel PPh3 upon reduction whereas complex 3 exhibits chemical reversibility and (ii) Under CO, complex 3 reacts with CO affording a new compound P, which shows a reversible wave at E-1/2 similar to-0.9 V (vs. ferrocenium/ferrocene couple). The presence of CO assists the formation of 1 after electrochemically induced loss of PPh3 during the voltammetric experiment of 2. Using DFT calculations we provide an explanation for the difference in stabilities between the Fe-PPh3 and Fe-P(OEt)(3) bonds.