Facile synthesis of 1,5-disubstituted 1,2,3-triazoles by the regiospecific alkylation of a ruthenium triazolato complex

Abstract

The alkylation of the N(2)-bound ruthenium triazolate [Ru]N₃C₂HCO₂Et (2, [Ru] = (η⁵-C₅H₅)(dppe)Ru, dppe = Ph₂PCH₂CH₂PPh₂) with benzylbromides is reported. The regiospecific alkylation of 2, which results from the [3 + 2] cycloaddition of ethyl propiolate with [Ru]-N₃ (1), gives a series of cationic N(1)-bound N(3)-alkylated-4-ethoxycarbonyl triazolato complexes {[Ru]N₃(CH₂R)C₂HCO₂Et}[Br] (3a, R = 4-CH₂Br-C₆H₄; 3b, R = 3,5-(CH₂Br)₂-C₆H₃; 3c, R = 2,6-F₂-C₆H₃; 3d, R = 4-CN-C₆H₄) and the subsequent cleavage of the Ru–N bond of 3a–3d gives N(1)-alkylated-5-ethoxycarbonyl triazoles N₃(CH₂R)C₂HCO₂Et (4a–4d) and [Ru]-Br, which, on reacting with sodium azide, would afford [Ru]-N₃ (1) thus forming a reaction cycle. The treatment of {[Ru]N₃(CH₂C₆F₅)C₂HCO₂Et}[Br] (3e) with sodium azide in refluxing ethanol gives the free triazole N₃(CH₂C₆F₅)C₂HCO₂Et (4e) and 1. The treatment of 2 with an equivalent of 3a affords a dinuclear bis(triazolato) complex {α,α′-bis([Ru]N₃C₂HCO₂Et)-p-xylene}[Br]₂ (5) and an organic bis(triazole) complex α,α′-bis(N₃C₂HCO₂Et)-p-xylene (6). The treatment of 2 with CF₃COOH in CHCl₃ at room temperature affords a mixture of N(2)-bound 1H- and 3H-4-ethoxycarbonyl triazolato complexes {[Ru]N₃HC₂HCO₂Et}[CF₃COO] (1H-7) and (3H-7) in a ratio of 5 : 2. The structures of 4e, 5 and 1H-7 were confirmed by single-crystal X-ray diffraction analysis.