Synthesis, structure and electronic properties of N-dialkylamino- and N-alkoxy-1,2,4-triazol-3-ylidene ligands

4-Amino- and 4-alkoxy-1,2,4-triazoles 4a–d and 6 were readily obtained from the reaction of N,N-dimethylformamidazin dihydrochloride 3 with hydrazines 2 and hydroxylamine 5. Alkylation of compounds 4a–d and 6 by MeOTf or MeI afforded azolium salts 9–11, which in turn were transformed into Rh(I) carbene complexes 13–15, Ag carbenes 16, and cationic Rh(I) bis-carbenes 17. Additionally, complexes 13 and 15 were transformed into dicarbonyl derivatives 18 and 19, and the carbonyl stretching frequencies of these compounds were used to evaluate the effect of the amino and alkoxy groups in the σ-donor ability of these 1,2,4-triazol-3-ylidenes.

Graphical abstractA synthesis of 4-amino- or alkoxy-1,2,4-triazolium salts I has been key for the obtention of 1,2,4-triazol-3-ylidene derivatives such as neutral RhCl(carbene)(COD) II and cationic Rh(carbene)2(COD) III complexes. The effect of the amino- and alkoxy groups in the σ-donor ability of these carbenes has been comparatively evaluated from the ν(CO) stretching frequencies of RhCl(carbene)(CO)2 complexes IV.Figure optionsDownload full-size imageDownload as PowerPoint slide