Quantum-Chemical Study of the Structure of Amidinyltetramethoxycarbonylcyclopentadiene and Its Hg(II) and Tl(I) Complexes

It has been shown by DFT CAM-B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p)/SDD calculations that the polydentate amidinyltetramethoxycarbonylcyclopentadienyl ligand and its Hg(II) and Tl(I) complexes are most stable in the form of ylide isomers, in which the hydrogen or metal atom is bonded to the terminal nitrogen atom of the amidinium fragment and, in the case of metal complexes, is additionally coordinated by the π-system of the cyclopentadiene ring. Alternative isomers with hydrogen or metal atoms bonded to carbon atoms of the cyclopentadiene ring or to carbonyl oxygen atoms of methoxycarbonyl substituents are energetically less stable by Δ E ZPE = 4.1–15.1 kcal/mol.