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

Abstract

The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co 2(CO) 8 or Co 2(CO) 6(X), (X = dppa, dppm), gave rise to the formation of substituted ethynylcobalt complexes containing one or two Co 2(CO) 6 or Co 2(CO) 4(X) units, 2-[Co 2(CO) 4(X){μ 2-η 2-(SiMe 3)C 2}]-5-(Me 3SiC C)C 4H 2S (X = 2CO ( 1), dppa ( 3) or dppm ( 4)) and 2,5-[Co 2(CO) 4(X){μ 2-η 2-SiMe 3C 2}] 2C 4H 2S (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-[Co 2(CO) 4(μ-X){μ 2-η 2-SiMe 3C 2}]-5-(C CH)C 4H 2S (X = dppa ( 7), dppm ( 8)) and 2,5-[Co 2(CO) 4(μ-dppm){μ 2-η 2-HC 2}] 2C 4H 2S ( 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.