Thermolysis of the tetrahedrane cluster PhCCo3(CO)(3)(mu-CO)Cp-2 with the unsaturated diphosphine ligands (Z)-Ph2PCH=CHPPh2 and 4,5-Bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): Redox properties and molecular structure of PhCCo3(CO)(mu-CO)[(

摘要

Thermolysis of the tricobalt cluster PhCCo3(CO)(3)(mu-CO) Cp-2 ( 1) with the diphosphine ligands ( Z)-Ph2PCH=CHPPh2 and 4,5-bis(diphenylphosphino)-4-cyclopenten- 1,3-dione (bpcd) has been examined and found to give the diphosphine-substituted clusters PhCCo3(CO)[(Z)-Ph2PCH=CHPPh2](mu-CO) Cp-2 ( 2) and PhCCo3(CO)(bpcd)(mu-CO) Cp-2 ( 3) in moderate yield. The new compounds 2 and 3 have been isolated and characterized in solution by IR and NMR (H-1 and P-31) spectroscopies. VT P-31 NMR data reveal that the chelating diphosphine ligand is fluxional in solution and exhibits a rocking motion between the axial and equatorial sites that renders both phosphorus moieties identical at ambient temperature. The molecular structure of PhCCo3(CO)[( Z)-Ph2PCH=CHPPh2](mu-CO) Cp-2 ( 2) has been determined by X-ray crystallography. PhCCo3(CO)[(Z)-Ph2PCH=CHPPh2](mu-CO) Cp-2 crystallizes, as the CH2Cl2 solvate, in the monoclinic space P2(1)/ n, a = 16.822( 2) angstrom, b = 10.554( 1) angstrom, c = 23.135( 3) angstrom, = 100.944( 2)degrees, V = 4032.4( 8) angstrom(3), Z = 4, and d(calc) = 1.537 Mg/m(3); R = 0.0488, R-w = 0.0725 for 9431 reflections with I > 2 sigma(I). The solid-state structure of cluster 2 establishes the chelating nature of the ancillary ( Z)Ph2PCH=CHPPh2 ligand at the unique Co(CO) P-2 center via coordination at an equatorial and an axial site. The redox behavior of clusters 2 and 3 has been explored by cyclic voltammetry and chronocoulometry. Each cluster reveals the presence of two one-electron oxidations of common origin due to the oxidation of a Co Co bonding orbital. Whereas cluster 2 does not exhibit an accessible reduction process in CH2Cl2, a ligand-based one-electron reduction was found for cluster 3 given its low-lying pi* LUMO associated with the bpcd ligand. The electrochemical data for clusters 2 and 3 are discussed with respect to the reported redox chemistry for this genre of tricobalt cluster and the bpcd ligand.