PROTONATION OF CP(CO)(PPH(3))RUC-CPH - FORMATION OF CATIONIC PHENYLACETYLENE AND PHENYLVINYLIDENE COMPLEXES AND SUBSEQUENT REACTION WITH ETHYLENE-OXIDE TO FORM THE NET-[2+3]-CYCLOADDUCT [CP(CO)(PPH(3))RU=(CCH(PH)CH2CH2O)-OVER-BAR](+)

Protonation of the alkynyl complex Cp(CO)(PPh(3))RuC=CPh (1) at low temperature affords quantitatively the vinylidene complex [Cp(CO)(PPh(3))Ru=C=CH(Ph)](+) (3), which upon warming to room temperature forms an equilibrium with the eta(2)-phenylacetylene complex [Cp(CO)(PPh(3))Ru(eta(2)-HC=CPh)](+) (4), with the latter predominating. Subsequent reaction with ethylene oxide yields the cyclic oxacarbene complex [Cp(CO)(PPh(3))Ru=CCH(Ph)CH2CH2O](+) (5), which can be regarded as the result of a net [3+2] cycloaddition reaction between 3 and ethylene oxide. Deprotonation of 5 affords the corresponding neutral cyclic vinyl complex Cp(Co)(PPh(3))RuC=C(Ph)CH2CH2O (6), which can in turn be protonated to regenerate 5 in a diastereoselective manner. The structures of complexes 5 and 6 were determined by X-ray crystallography.