MIND0/3 Study of Cyclopentadienylidene and Its Insertion into Molecular Hydrogen

The lowest singlet and triplet states of cyclopentadienylidene (1) have been studied with the MIND0/3 method. It is found that · the ground state of 1 is a spin triplet, which is supported by experimental finding and some previous calculations. The relationship between the geometrical and electronic structures for these states is also discussed. In studying the least-motion and non-least-motion paths of the hydrogen •insertion of 1, it is found that the latter is preferred energetically. In addHion, as in the cases of other similar carbenehydrogen reactions, the concerted non-least-motion path consists of, in order, electrophilic and nucleophilic steps. However, for the present reaction, in order to distinguish the two steps, the charges on the hydrogens, rather than that on the carbenic center, should be monitored