Dative and Electron-Sharing Bonding in C2 F4.

The reaction pathway for the rupture of the carbon-carbon double bond of C2 F4 has been calculated with ab initio methods at the CASSCF(8,8)+NEVPT2/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels and with density functional theory using M06-L and M06-2X functionals in conjunction with aug-cc-pVTZ basis sets. The calculations suggest that the bond dissociation pathway proceeds by a nonlinear reaction course without an activation barrier yielding the CF2 fragments in the (1 A1 ) ground state. A bonding analysis indicates that there is a continuous change in the electronic structure of the CF2 fragments during the elongation of the C-C distance from a (3 B1 ) excited state at the equilibrium geometry of C2 F4 to the (1 A1 ) ground state. EDA-NOCV calculations suggest that the carbon-carbon interactions in C2 F4 at equilibrium distance and longer C-C values up to ≈1.60 Å are best described in terms of electron-sharing bonding between the CF2 fragments in the (3 B1 ) excited state. At longer distances, the situation changes toward dative bonding between CF2 fragments in the (1 A1 ) ground state.