ON THE REACTIVITY OF ACETYLENES COORDINATED TO COBALT .9. EFFECTS OF SUBSTITUTION AND COORDINATION ON THE C-13-NMR CHEMICAL-SHIFTS OF THE SP CARBONS OF (MU(2)-R(1)C(2)R(2))CO-2(CO)(6) COMPLEXES - MOLECULAR-STRUCTURE OF (MU(2)-PHC(2)SIPH(3))CO-2(CO)(6)

Thirty-four (mu(2)-R(1)C(2)R(2))Co-2(CO)(6) complexes (14 new) were prepared and characterized by their IR v(CO) and H-1- and C-13-NMR spectra. The C-13-NMR chemical shifts of the coordinated sp carbon atoms were correlated with those of the corresponding free acetylenes. This indicated that the interaction between the R(1) and R(2) groups and the C2Co2(CO)(6) moiety is very sensitive not only to the donor/acceptor character of R(1) and R(2) but also to the orbital symmetry of the atoms attached directly to the C(sp) atoms. The changes of the delta(C-13) values of the C(sp) atoms upon coordination were also analyzed in these terms. It is concluded that although the dinuclear mu(2)-coordination of the acetylene results in a high degree of excitation the stability of the C2Co2(CO)(6) moiety diminished the reactivity of the organic ligand. Differences in the reactivity of the (mu(2)-R(1)C(2)R(2))Co-2(CO)(6) complexes in carbonylation are also discussed. The crystal and molecular structure of (PhC(2)SiPh(3))Co-2(CO)(6) was determined by single crystal X-ray diffraction. This compound crystallizes in the orthorhombic Pbca space group with a = 28.790(2) Angstrom, b = 11.577(1) Angstrom, c = 17.833(2) Angstrom, Z = 8. The structure was determined with R = 0.039, R(w) = 0.036.