Synthesis, characterisation and electrochemical properties of Cr(0) aminocarbene complexes containing condensed heteroaromatic moiety

The series of new aminocarbene complexes of chromium(0) containing condensed benzo-heteroaromatic substituents (N-methylindol-2-yl (1), N-methylindol-3-yl (1a), benzofuran-2-yl (2) and benzothien-2-yl (3)) were synthesised and fully characterised. The crystal structure of 3 was elucidated from single-crystal x-ray diffraction. Cyclic voltammetry was used to determine oxidation and the reduction properties of the synthesised compounds. The experimental results were compared with quantum chemical calculations performed with the density functional theory. The results show similar trends as other five-membered heterocyclic carbenes published previously. The first oxidation potentials are, in decreasing order, 2, 3 and 1. The oxidation potential of 1a is approximately 100 mV lower than that of 1. The reduction proceeds easily for 2 and 3 with close reduction potential values (−1.62 V and −1.63 V). On the other hand, the reduction of 1 and 1a is more difficult (−1.92 V and −2.07 V).