Synthesis and physical properties of α,ω-bis[Co 2(CO) 6{μ-η 2:η 2-C(R)C}]oligothiophenes

Abstract

α,ω-Bis[Co 2(CO) 6{μ-η 2:η 2-C(R)C}]oligothiophene derivatives ( 6– 10), in which two dicobalt hexacarbonyl acetylides are π-conjugated onto both terminals of the oligothiophene, were prepared by the reaction of the α,ω-bis(alkynyl)oligothiophenes ( 1– 5) with Co 2(CO) 8. The molecular structures of new compounds were identified by spectroscopic methods and elemental analysis. In cyclic voltammetry of the clusters 6– 10, two oligothiophene-based oxidation processes (one for 7) occur between −0.2 and 1.5 V, and the one reductive process of the metal cluster moieties occurs 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 reactions at ambient temperature. The clusters 6– 10 commonly exhibit three characteristic bands: a moderately intense, high-energy band, strong medium-energy band and weak-low energy band. The high-energy bands are attributed to the a π–π* localized excitation. The medium- and low-energy bands may be ascribed to the metal-to-ligand (d Co–π* ligand) charge-transfer transitions of the cluster moiety.