Synthesis and crystal structure of an iron triazole complex resulting from the unexpected ligand cleavage of a triazolium carbene precursor

Abstract

Typically reactions of N-heterocyclic carbenes with transition metals are straightforward and require a carbene salt, a base strong enough to deprotonate such a salt and a metal. Yet when carbene precursors are in the form of triazolium salts, reaction may not proceed as easily as expected. In our work, we intended to obtain a triazolylidene complex of iron(II) chloride, but due to the presence of small amounts of water in the tetrahydrofuran solvent used, bis(acetonitrile)tetrakis(1-benzyl-1H-1,2,4-triazole-κN 4)iron(II) μ-oxido-bis[trichloridoferrate(III)] acetonitrile disolvate, [Fe(C9H9N3)4(CH3CN)2][Fe2Cl6O]·2CH3CN – an interesting anion with a linear geometry of the O atom – was formed instead of the iron carbene complex. Reaction proceeded via cleavage of the alkyl N-substituent of the triazolium salt. The formation of the product was confirmed by X-ray crystallography. The crystal structure and possible reaction pathways are discussed.