Synthesis, structures and comparative electrochemical study of 2,5-bis(trimethylsilylethynyl)thiophene coordinated cobalt carbonyl units

The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co2(CO)8 or Co2(CO)6(X), (X=dppa, dppm), gave rise to the formation of substituted ethynylcobalt complexes containing one or two Co2(CO)6 or Co2(CO)4(X) units, 2-[Co2(CO)4(X){μ2-η2-(SiMe3)C2}]-5-(Me3SiCC)C4H2S (X=2CO (1), dppa (3) or dppm (4)) and 2,5-[Co2(CO)4(X){μ2-η2-SiMe3C2}]2C4H2S (X=2CO (2), dppa (5) or dppm (6)). Desilylation of the non-metallated and metallated alkynes in 3, 4 and 6 occurred on treatment with KOH and tetrabutylammonium fluoride to give 2-[Co2(CO)4(μ-X){μ2-η2-SiMe3C2}]-5-(CCH)C4H2S (X=dppa (7), dppm (8)) and 2,5-[Co2(CO)4(μ-dppm){μ2-η2-HC2}]2C4H2S (9), respectively. Crystals of 6 suitable for single-crystal X-ray diffraction were grown and the molecular structure of this compound is discussed. A comparative electrochemical study of all these complexes is presented by means of the cyclic and square-wave voltammetry techniques.