Coinage Metal Complexes of the Carbenic Tautomer of a Conjugated Mesomeric Betaine Akin to Nitron

• Published in: Molecules (Basel, Switzerland) Switzerland), 2017-07, Vol.22 (7), p.1133
• Main Authors: Thie, Charlotte, Bruhn, Clemens, Leibold, Michael, Siemeling, Ulrich
• Format: Article
• Language: English
• Subjects: 1,2,4-triazol-5-ylidene; Betaine; Betaine - chemistry; Chemistry; coinage metals; conjugated mesomeric betaine; Coordination Complexes - chemical synthesis; Coordination Complexes - chemistry; Copper; Copper - chemistry; Copper chloride; crystal structure; Crystallography, X-Ray - methods; gold; Homology; Magnetic Resonance Spectroscopy - methods; Materials science; Metal complexes; Methane - analogs & derivatives; Methane - chemistry; Models, Molecular; Molecular Structure; N-heterocyclic carbene; NMR; Nuclear magnetic resonance; Reagents; Salts; silver; Spectroscopy; Structure-Activity Relationship; Triazoles - chemical synthesis; Triazoles - chemistry
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules22071133

This study was motivated by our recent observation that the analytical reagent Nitron ( ) is an "instant carbene", whose reaction with coinage metal salts MX afforded complexes of its carbenic tautomer 1,4-diphenyl-3-phenylamino-1,2,4-triazol-5-ylidene ( '). Our aim was to establish an alkyl homologue of in order to achieve a carbenic tautomer of higher donicity. For this purpose 1- -butyl-4-methyl-1,2,4-triazol-4-ium-3- -butylaminide ( ) was synthesized. Its reactions with MX afforded complexes of the carbenic tautomer 1- -butyl-3- -butylamino-4-methyl-1,2,4-triazol-5-ylidene ( '). With a stoichiometric ratio of 1:1 complexes of the type [MX( ')] were obtained. A ratio of 2:1 furnished complexes of the type [MX( ')₂] or [M( ')₂]X. ' is a better σ-donor and less electrophilic than ' according to NMR spectroscopic data of H[BF₄] and ' = Se, respectively, and IR spectroscopic data of [RhCl( ')(CO)₂] confirm that its net electron donor capacity is superior to that of '. A comparison of the complexes of ' and ' reveals two pronounced structural differences. [CuX( ')₂] (X = Cl, Br) exhibit more acute C‒Cu‒C bond angles than [CuX( ')₂]. In contrast to [CuCl( ')], [CuCl( ')] aggregates through Cu···Cu contacts of ca. 2.87 Å, compatible with cuprophilic interactions. These differences may be explained by the complementary steric requirements of the -Bu and the Me substituent of '.