Rhenabenzenes and Unexpected Coupling Products from the Reactions of Rhenacyclobutadienes with Ethoxyethyne

Treatment of Na­[Re­(CO)5] with methyl 3-(naphthalen-1-yl)­propiolate
(NpCCCO2Me) followed by acetyl chloride and alcohols
ROH (R = Me, nPr) afforded the rhenacyclobutadiene
complexes Re­{-C­(Np)C­(CO2Me)­C­(OR)}­(CO)4. Reactions of these rhenacyclobutadiene complexes with HCCOEt
produced the rhenabenzene complexes Re­{-C­(Np)C­(CO2Me)­C­(OR)CHC­(OEt)}­(CO)4 and new rhenacyclobutadienes with a pendant vinyl substituent Re­{-C­(Np)C­(C­(OR)CH­(CO2Et))­C­(OMe)}­(CO)4. In the vinyl-substituted
rhenacyclobutadiene products, the ethyl of the ester group is from
the alkyne HCCOEt, the alkyl of the ReC­(OR) group is from
the ester group of the starting rhenacyclobutadienes, and the alkyl
group of the OR of the vinyl substituent is from the ReC­(OR) group
of the starting rhenacyclobutadienes. A plausible mechanism for the
formation of the vinyl-substituted rhenacyclobutadienes is discussed.