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)C ₂SiMe₃ (1), Me₃SiC₂(C₁₃H₆O)C ₂SiMe₃ (2), Me₃SiC₂(C₄H₂S)₂C ₂SiMe₃ (3), Me₃SiC₂(C₁₄H₇Fc)C ₂SiMe₃ (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 Me₃SiCCRCCSiMe₃ and HCCRCCH, 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.