Theoretical studies on the aromaticity of η 5-cyclopentadienyl cobalt dithiolene complexes

Abstract

Some η 5-cyclopentadienyl cobalt dithiolene complexes CpCoS 2C 2R 2 have been optimized at B3LYP/6-311++G(d) level. The optimized geometries agree well with experiment. The analyses of nature bond orbital and nucleus-independent chemical shift (NICS) at B3LYP/6-311++G(d) and GIAO-B3LYP/6-311++G(d) levels reveal the aromatic character of the η 5-cyclopentadienyl cobalt dithiolene complexes. However, their aromaticity is weaker than that of the isolated CoS 2 C 2 + 1 . There are two reasons for the change of heterocyclic aromaticity of the metal dithiolene in the η 5-cyclopentadienyl cobalt dithiolene complexes with respect to that of the isolated CoS 2 C 2 + 1 . The better equalization of bond lengths in the isolated cation CoS 2 C 2 + 1 is the first reason. The other reason is that the contribution to the NICS from the metallic cobalt atom is much larger in the isolated cation CoS 2 C 2 + 1 . The planar character of cyclopentadienyl is destroyed slightly in the complexes. At the same time, the size of cyclopentadienyl (Cp) becomes bigger than the isolated Cp −1 and this is caused by the cobalt atom in the pentagon. The π-electron delocalization causes stronger aromaticity of the Cp in the complexes than that of the isolated Cp −1.