Structural and electrochemical study of metal carbonyl complexes with chelating bis- and tetrakis(diphenylphosphino)tetrathiafulvalenes

Several mono- and bimetallic complexes involving organometallic fragments such as M(CO)4 (M=Mo, W), Re(CO)3Cl and Fe(CO)3 coordinated to the chelating diphosphine 3,4-dimethyl-3′,4′-bis(diphenylphosphino)tetrathiafulvalene (P2) or tetraphosphine tetrakis(diphenylphosphino)tetrathiafulvalene (P4) have been synthesized and characterized. X-ray diffraction structures have been determined for P4[W(CO)4]2, P2Re(CO)3Cl, P2Fe(CO)3 and P4[Fe(CO)3]2. Octahedral geometries around the metallic center are observed for the tungsten and rhenium complexes, with a fac arrangement of the ligands for the latter, whereas slightly distorted trigonal bipyramid are found for both iron counter parts. Although the complexes are more difficult to oxidize than the corresponding free phosphines, as evidenced by cyclic voltammetry measurements, the first oxidation potentials remain in the usual range, thus offering the opportunity to generate stable radical cation salts. In the case of Fe complexes, the first oxidation wave corresponds to the formation of paramagnetic d7 Fe(I) species, whereas in the Mo, W and Re complexes the metallic center is much more difficult to oxidize than the TTF core.