Synthesis, Characterization, Structures and Comparative Electrochemical Study of 2,4‐Bis(trimethylsilylethynyl)thiophene Coordinated Carbonylcobalt Units

Abstract

The reaction between 2,4-dibromothiophene and trimethylsilylacetylene (TMSA) in the presence of Pd(PPh 3 ) 4 , CuI and triethylamine gave rise to the formation of 2,4-bis(trimethylsilylethynyl)thiophene (2,4T) and 4-bromo-2-(trimethylsilylethynyl)thiophene (2,4TЈ). Complexes 1, 2, 3 or 1Ј were obtained by direct reaction between Co 2 (CO) 8 and 2,4T or 2,4TЈ, respectively. (Diphenylphosphanyl)methane-substituted alkyne carbonyl complexes 4, 5, 6 and 2Ј were prepared by substitution reaction of carbonyl ligands in the presence of Me 3 NO at the Co 2 (CO) 6 units of 1, 2, 3 and 1Ј, respectively. Desilylation of the non-metallated and metallated al-

The effect of thiophene ring substitution position on the properties and electrochemical behaviour of alkyne–dicobaltcarbonylthiophene complexes

“…2-4) and with the proposed structures (Schemes A-D) and comparable to those of the known cobalt-substituted 2,5-[10b] and 2,4-bis(trimethylsilylethynyl)thiophene [11] complexes. The 1 H and 13 C{ 1 H} NMR data of all the complexes are summarized in Tables 1-4.…”

“…This preference is also observed in the synthesis of the analogous complexes 2-[Co 2 (CO) 6 {l 2 -g 2 -(SiMe 3 C 2 )}]-4-(Me 3 SiC"C)C 4 H 2 S and 2-(Me 3 SiC"C)-4-[Co 2 (CO) 6 {l 2 -g 2 -(SiMe 3 C 2 )}]C 4 H 2 S [11]. This result can be explained by electronic factors, as judged by the 13 C NMR shifts for the alkyne C-atoms in C (Table 4).…”

“…1). It can be observed that these molecules have k max at 331 [22], 311 and 277 nm [11], respectively. However, k max for 3,4-bis(trimethylsilylethynyl)thiophene (258 nm) is significantly blue-shifted, thus indicating a lesser overall conjugation in this molecule.…”

“…As alkynyl or polyynediyl bridging ligands have been shown to be efficient in allowing the passage of electronic effects between redox-active centres [8e,f,9,10], and therefore the electronic properties and the use of a thiophene-based diethynyl ligand should lower the energy barriers and facilitate electron transfer, we have recently reported the reactivity and the electrochemical behaviour of 2,5-[10b] and 2,4-bis(trimethylsilylethynyl)thiophene [11] derivatives, comparing the effects of the substitution position of the -C"C-SiMe 3 groups on the thiophene ring. These results encouraged us to study the analogous 2, 3-and 3,4-bis(trimethylsilylethynyl)thiophene ligands that in contrast with the well-studied 2,5-bis(trimethylsilylethynyl)thiophene have received little attention [12].…”

Synthesis, Structure and Electrochemical Properties of Triarylamine Bridged Dicobaltdicarbon Tetrahedrane Clusters

“…Interpolation of other -conjugated moieties between the cluster centres gives rise to less strongly coupled to decoupled systems [48][49][50], with results from electrochemical studies being consistent with a significant contributions from both through-space and through-bond effects to the stabilisation of the one-electron redox products in some cases [51].…”