Preparation, Structure, and Reactivity of 1,3,4‐Triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene, a New Stable Carbene

Abstract

Stable to 150 °C, the heterocyclic carbene 1 is characterized by the typical reactivity of a nucleophilic carbene. Dihydrotriazole 1 can be prepared by simple thermal decomposition of its methanol adduct. X‐ray crystal structure analysis, ab initio calculations, and reactivity studies confirm the nucleophilic carbene character of 1.

Synthesis and properties of heteroaromatic carbenes of the imidazole and triazole series and their fused analogues

“…[276][277][278] Several of the studies showed that some heterocyclic carbenes become unstable upon heating. 103,168,279 Interestingly, reactions of this type have not been studied until recently. 4.1.1.…”

“…Rearrangement of N-phosphanylazolylidenes. 168 However, the processes that take place at elevated temperatures in the absence of other reactants have not been studied.…”

“…7,9,168,198 As such, these reagents can act as alcohols, thiols or amines. However, such insertion products are generally labile and upon heating transform back into the original carbenes.…”

“…As an example, 5-methoxy-1,3,4-triphenyl-5Н-1,2,4-triazoline 36B is relatively stable, and decomposes to a carbene and methanol only when heated at 80 C for 24 hours (Scheme 36). 168 On the other hand, 1,3-dimethyl-2-(N-morpholinyl)-2H-benzimidazoline sublimes when heated, which may be due to its reversible cleavage into the carbene and the amine. 198 The reactions with alcohols have been used to protect carbenic centers and to produce high quality carbenes.…”

“…168 The reaction of carbene 93A with CO2 was carried out by Kuhn et al, forming the adduct 93B (Scheme 93). 358 In both cases, zwitterionic compounds were obtained.…”