REACTION OF FCCCO(3)(CO)(9) WITH 2,3-BIS(DIPHENYLPHOSPHINO)MALEIC ANHYDRIDE (BMA) - X-RAY-DIFFRACTION STRUCTURE AND REDOX PROPERTIES OF (2)ETA(1)-C(FC)C=C(PPH(2))C(O)OC(O)](MU(2)-PPH(2))

The reaction between the tricobalt cluster FcCCo(3)(CO)(9) (1) (where Fc=ferrocenyl) and the redox-active diphosphine ligand 2,3-bis (diphen ylphosphino) maleic anhydride (bma) affords the new cluster Co-3(CO)(6 )[mu(2)-eta(2):eta(1)-C(Fc)C=C(PPh(2)) C(O)OC(O)](mu(2)-PPh(2)) (3) in refluxing 1,2-dichloroethane or toluene. The cluster FcCCo(3)(CO)(7)( bma) (2), a logical precursor to 3, was observed in solution by IR spe ctroscopy when cluster 1 and bma were refluxed in the low boiling poin t solvent CH2Cl2; however, putative 2 could not be isolated due to its rapid conversion to the final product 3. Cluster 3 has been fully cha racterized in solution by IR and NMR (C-13 and P-31) spectroscopy and in the solid state by X-ray diffraction analysis. ):eta(1)-C(Fc)C=C(PP h(2))C(O)OC(O)](mu(2)-PPh(2)), as the CH2Cl2 Solvate, crystallized in the triclinic space group P (1) over bar, a=10.4704(6), b=14.6033(8), c=14.787(1) Angstrom, alpha=102.973(5), beta=94.517(8), gamma=90.197(5 )degrees, V=2195.9(2) Angstrom(3), Z=2, D-calc=1.653 g cm(-3); R=0.041 1, R(w)=0.0449 for 3602 observed reflections with I>3 sigma(I). Cyclic voltammetric investigations of 3 in CH2Cl2 reveal the presence of thr ee reversible redox responses assigned to the 0/1(+), 0/1(-), and 1(-) /2(-) redox couples. The nature of the HOMO and the two lowest unoccup ied molecular orbitals (LUMO and SUMO) in 3 has been determined by car rying out extended Huckel calculations on the model compound Co-3(Co)( 6)[mu(2) eta(2):eta(1)-C(Fc)C=C(PH2)C(O)O](mu(2)-PH2), the results of which are discussed relative to the observed electrochemistry of 3 and related cluster compounds.