Synthesis and physical properties of alpha,omega-bis[Co-2(CO)(6){mu-eta(2):eta(2)-C(R) C}]oligothiophenes

alpha.omega-Bis[Co-2(CO)(6){mu-eta(2):eta(2)-C(R)=C}]oligothiophene derivat ives (6-10), in which two dicobalt hexacarbonyl acetylides are pi-conjugate d onto both terminals of the oligothiophene, were prepared by the reaction of the alpha,omega-bis(alkynyl)oligothiophenes (1-5) with Co-2(CO)(8). The molecular structures of new compounds were identified by spectroscopic meth ods and elemental analysis. In cyclic voltammetry of the clusters 6-10, two oligothiophene-based oxidation processes (one for 7) occur between - 0.2 a nd 1.5 V, and the one reductive process of the metal cluster moieties occur s between 0.0 and - 1.6 V, which is not present for the oligothiophenes (1- 5). The silence of the expected electronic communication of the clusters 6- 10 may be attributed to the reduction process followed by fast chemical rea ctions at ambient temperature. The clusters 6-10 commonly exhibit three cha racteristic bands: a moderately intense, high-energy band, strong medium-en ergy band and weak-low energy band. The high-energy bands are attributed to the a pi-pi* localized excitation. The medium- and low-energy bands may be ascribed to the metal-to-ligand (d(Co)-pi(ligand)(*)) charge-transfer tran sitions of the cluster moiety. (C) 2000 Elsevier Science S.A. All rights re served.