[3+2] Cycloaddition of ruthenium azido complex with Ethyl propiolate and related reactions

The [3+2] cycloaddition reaction of ethyl propiolate with ruthenium azido complex [Ru]−N3 (1, [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) has been investigated. The metal-bound heterocyclic complex produced is N(2)-bound triazolate [Ru]N3CHCO2Et (2). A regiospecific alkylation happens by treatment of 2 with organic halides and gives a series of cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato complexes {[Ru]N3(R)C2HCO2Et}[X] (3a, R = CH3, X = I; 3b, R = CH2Ph, X = Br; 3c, R = CH2C6F5, X = Br; 3d, R = CH2CN, X = I; 3e, CH2CO2CH3, X = Br) and the following cleavage of the Ru-N bond of 3a and 3b gives ruthenium halides and N(1)-alkylated five-membered-ring organic triazoles N3(R)C2HCO2Et (4a, R = CH3; 4b, R = CH2Ph). The structures of 2 and 3c have been determined by single-crystal X-ray diffraction analysis.