[GRAPHICS]
Benzocyclopropene and cyclopropa[b]naphthalene react with dichloro-bis(tric
yclohexylphosphine)methylideneruthenium, incorporating the metallacarbene t
o form unstable 3-ruthenacyclopentenes, which decompose to give o-xylylenes
that can be trapped as Diels-Alder adducts by dimethyl acetylenedicarboxyl
ate. In contrast, bis(eta (5)-cyclopentadienyl)methylidenetitanium forms mo
derately stable 2- and 3-titanacyclopentene complexes.