Successful strategies have previously been developed to stabilize the σ2π0 singlet states of carbenes, relative to σ1π1 triplet states. However, little or no attention has been paid to the stabilization of the σ0π 2 singlet states. We present two simple strategies to stabilize the σ0π2 singlet states of carbenes, relative to both the σ2π0 singlet and σ1π 1 triplet states. These strategies consist of destabilization of the carbene σ orbital by two, adjacent, sp2 nitrogen lone pairs of electrons and stabilization of the carbene 2p-π orbital by incorporating it into a five-membered ring, containing two double bonds, or into a six-membered ring, containing two double bonds and a sixth atom that has a low-lying empty π orbital. B3LYP, CASPT2, and CCSD(T) calculations have been performed in order to assess the success of these strategies in creating derivatives of cyclopenta-2,4-dienylidene and cyclohexa-2,5-dienylidene with σ0π6 singlet ground states. Differences between the calculated geometries and binding energies of the Xe complexes of the σ0π6 singlet ground state of 2,5- diazacyclopentadienylidene (5) and the σ2π0 singlet states of CH2 and CF2 are discussed.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry