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

New dimeric η2-diyne complexes of cobalt [{Co2(CO)6}2(diyne)] (diyne=Me3SiC2(C13H8)C2SiMe3 (1), Me3SiC2(C13H6O)C2SiMe3 (2), Me3SiC2(C4H2S)2C2SiMe3 (3), Me3SiC2(C14H7Fc)C2SiMe3 (Fc=ferrocenyl) (4), HC2(C13H8)C2H (5), HC2(C13H6O)C2H (6), HC2(C4H2S)2C2H (7) and HC2(C14H7Fc)C2H (8)) have been prepared in good yields from the reaction of [Co2(CO)8] with half an equivalent of the appropriate diyne ligands Me3SiCCRCCSiMe3 and HCCRC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 1H-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.