Novel heteroarene complexes of chromium (O)

Abstract

Novel π-heteroarene complexes of the type (T16-arene)Cr(CO)3 were synthesized. The reactivity of thio- and nitro-heteroarene rings towards TI-coordination to a Cr(CO)3-moiety were investigated. Two different synthetic routes were implemented to synthesize'the TI-coordinated products. It was found that the thio-heteroarene complexes were obtained in a high yield on treatment with trisamrnine(tricarbonyl)chromium, while higher yields were obtained for the nitroheteroarene complexes on treatment with hexacarbonylchromium. The arene ligands under investigation were 3,6-dimethylthieno[3,2-b ]thiophene, quinoline and phenazine. The synthesis of the (116-quinoline)Cr(CO)3 complex has proved to be more arduous than was expected and several methods were implemented to synthesize the desired product. In the end two products were isolated, both TI-coordinated to a Cr(CO)3-moiety, but neither resembling the target complex. Instead, nucleophilic addition occurred at the 2-position of both products and the lone pair of the nitrogen atom was blocked by a substituent. These complexes were fully characterized and the proposed structure formulations were confirmed by single crystal X-ray determinations. Known (T16-arene)Cr(CO)3 complexes were investigated with regard to activation and stabilization of the bridging arene ligand. The ligands benzo[ b ]thiophene and dibenzothiophene were monolithiated and treated with group IV (Ti), group VII (Mn, Re) and group X (Pt) transition metals at low temperatures to yield a,1t-bimetallic heteroarene complexes. The first o, π-bimetallic dibenzothiophene complexes were synthesized by this method. The yields of these complexes were, however, very low. From the spectroscopic data it was clear that the activation of the dibenzothiopheneCr(CO)3 complex towards coordination to the second metal, i.e. the a-bonded species, occurred on the same ring fragment as where the TI-coordination took place. In an attempt to improve the yield, another synthetic route was investigated and this led to the preparation of the a-dibenzothiophene complex, 111-dibenzothienyl-Re(CO)5. The synthetic method using this a-complex as precursor was unfortunately unsuccessful. All the new bimetallic compounds were fully characterized by means of NMR spectroscopy, infrared spectroscopy as well as mass spectrometry.