Dependence of the structure and stability of cyclocumulenes and cyclopropenes on the replacement of the CH₂ group by titanocene and zirconocene: a density functional theory study

Abstract

Density functional theory (DFT) studies of the energetics of the isomers of C₅H₄-cyclocumulene (1), ethynylcyclopropene (2), diethynylmethane (3), and their organometallic analogues obtained by replacing the CH₂ groups by Cp₂Ti and Cp₂Zr (4-6)show that the relative energies of the hydrocarbons are dramatically altered in the transition-metal analogues. The metallacyclocumulenes are comparable in energy to 5 and 6. The relative energies also explain the experimental observation that the metallacyclopropene (5) is more favorable for the Ti complex. Substituents on the carbon skeleton help to fine-tune the energetics. The bonding situations in 4 and the recently characterized five-membered zirconacyclopentyne complex 9 are very similar and are in tune with their structures.