BIDENTATE LIGAND SUBSTITUTION IN PHCCO3(CO)9 - SYNTHESIS, MOLECULAR-STRUCTURE, AND REDOX REACTIVITY OF PHCCO3(CO)7(CIS-PH2PCH=CHPPH2)

The synthesis of PhCCo3(CO)7(cis-Ph2PCH=CHPPh2) (2) from PhCCo3(CO)9 (1) and the bidentate phosphine cis-Ph2PCH=CHPPh2 is described. Cluster 2 is readily prepared in moderate to high yield using a variety of procedures. The diphosphine ligand in 2 bridges adjacent cobalt atoms as shown by C-13 and P-31 NMR spectroscopic measurements and X-ray diffraction analysis. PhCCo3(CO)7(Cis-Ph2PCH--CHPPh2) crystallizes in the monoclinic space group P2(1)/c with a = 12.7065 (9), b = 18.385 (2), c = 15.943 (1) angstrom, beta = 98.025 (6)-degrees, V = 3688.0 (5) angstrom3, and Z = 4. Full-matrix least-squares refinement yielded R = 0.0445 for 2021 (I > 3sigma(I)) reflections. The redox properties of 2 have been examined by using cyclic and rotating disk electrode voltammetric techniques. In CH2Cl2 solvent, 2 exhibits reversible 0/-1 and 0/+1 redox couples. The reversibility of the 0/+1 redox couple is highly dependent on the temperature and the nature of the solvent. Use of MeCN or THF as solvent leads to an irreversible, multi-electron oxidation. The electrochemistry of 2 is compared to the known cluster PhCCo3(CO)7(dppe).