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 pr epared and characterized by their IR v(CO) and H-1- and C-13-NMR spect ra. The C-13-NMR chemical shifts of the coordinated sp carbon atoms we re correlated with those of the corresponding free acetylenes. This in dicated 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 c haracter of R(1) and R(2) but also to the orbital symmetry of the atom s 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 the se terms. It is concluded that although the dinuclear mu(2)-coordinati on of the acetylene results in a high degree of excitation the stabili ty 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 s ingle crystal X-ray diffraction. This compound crystallizes in the ort horhombic 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.