Protonation of Cp(CO)(PPh 3) RuCCPh: Formation of cationnic phenylacetylene and phenylvinylidene complexes and subsequent reaction with ethylene oxide to form the net [2 + 3] cycloadduct [Cp(CO)(PPH 3)Ru=CCH(Ph)CH 2CH 2O] +

Abstract

Protonation of the alkynyl complex Cp(CO)(PPh 3)RuCCPh ( 1) at low temperature affords quantitatively the vinylidened complex [Cp(CO)(PPh 3)RuCCH(Ph)] + ( 3), which upon warming to room temperature forms an equilibrium with the η 2- phenylacetylene complex [Cp(CO)(PPh 3)Ru( η 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)CH 2CH 2O] + ( 5), which can be regarded as the result of a net [3+2] cycloaddition reaction between 3 and ethylene oxide. Depronation of 5 affords teh corresponding neutral cyclic vinyl complex [Cp(CO)(PPH 3)RuC=C(Ph)CH 2CH 2O] + ( 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.