Synthesis, electrochemistry and structural characterization of new dimeric cobalt η2-alkyne carbonyl complexes

New dimeric eta(2)-diyne complexes of cobalt [{Co-2(CO)(6)}(2)(diyne)] (diyne = Me3SiC2(C13H8)C2SiMe3 (1), Me3SiC2(C13H6O)C2SiMe3 (2), Me3SiC2(C4H2S)(2)C2SiMe3 (3), Me3SiC2(C(14)H(7)Fc)C2SiMe3 (Fc = ferrocenyl) (4), HC2(C13H8)C2H (5), HC2(C13H6O)C2H (6), HC2(C4H2S)(2)C2H (7) and HC2(C(14)H(7)Fc)C2H (8)) have been prepared in good yields from the reaction of [Co-2(CO)(8)] with half an equivalent of the appropriate diyne ligands Me3SiC drop CRC drop CSiMe3 and HC drop CRC drop CH respectively (R = 2,7-fluorenediyl, 2,7-fluoren-9-onediyl, 2,2'-bithiophene-5,5'-diyl, 9-ferrocenylmethylenefluorene-2,7-diyl). All the compounds 1-8 have been characterized by IR and H-1-NMR spectroscopies and mass spectrometry. The redox chemistry of these cobalt-alkyne molecules has been studied by cyclic voltammetry. The molecular structures of 2, 5, 6, 7 and 8 have been determined by single-crystal X-ray diffraction methods. Structurally, each of these displays two 'Co2C2' cores adopting the usual pseudo-tetrahedral geometry with the alkyne bond lying essentially perpendicular to the Co-Co vector. The original linearity of the diyne ligand is lost. (C) 2000 Elsevier Science S.A. All rights reserved.