Alkenes gas-phase

Admittedly, not all polycyclic tetrasubstituted olefins can be so simply constructed or described as bicyclo[m.n.O]alkenes. Gas-phase ion-molecule experiments (combined with some judicious but non-experimentally measured numbers) allowed the derivation of80 the formal enthalpy of hydrogenation of cubene (27a), i.e. the exothermicity of reaction 19 to form the saturated cubane (27b). 

The mechanism of Ru-alkylidene-catalyzed reactions has been investigated. Note that Grubbs first- and second-generation catalysts are 16-electron species, so if the first step involves complexation of an alkene to the metal, this process could occur in an associative or dissociative manner. Evidence suggests (see Scheme 11.5) that this occurs in a dissociative manner, however, first forming a 14-electron intermediate 25 and then 26a or 26b after complexation of the alkene. Gas-phase mass spectral evidence supports the initial formation of 25. Complexes similar to 26a and b have been isolated from reaction mixtures under appropriate conditions, but ruthenacyclobutane 27 has not been directly observed until quite recently.37... 

---