Triplet carbenes pathway determination

The rather short lifetime (a few nanoseconds) of the triplet excited carbene makes extensive studies of intermolecular processes difficult. However, the excited-state lifetime (60 ns) of triplet dimesitylcarbene (19c) is exceptionally large, probably because of decreased efficiency of both intermolecular and intramolecular deactivation pathways. Intermolecular rate constants for the reaction with CCI4, O2 and 1,4-cyclohexadiene have been determined. 

Fig. 25 Potential energy surfaces for the most feasible two-state reaction pathways for ethylene dimerization catalyzed by Cr(II)OH (If), via either a Cr-carbene mechanism or a metallacycle mechanism determined at the M06 level of theory. Also shown are the crossing points optimized at CASSCF level. The triplet metallacycle reaction pathway is depicted in blue, and the triplet Cr-carbene reaction pathway is shown in dark red. The quintet parts are in black. Energies are in kcal moP and relative to il. Bond lengths are in angstroms. Angles are in degrees...

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