Mono‐ and Di‐Mesoionic Carbene‐Boranes: Synthesis, Structures and Utility as Reducing Agents

Abstract

Mesoionic carbenes (MIC) of the 1,2,3-triazol-5-ylidene type are currently popular ligands in organometallic chemistry. Their use in main group chemistry has been rather limited. In this contribution we present mono-and di-MIC-boranes with MICs based on triazolylidenes. The synthesis involves in-situ deprotonation of the corresponding triazolium salts and their reaction with boranes to form the desired compounds. Whereas this reaction route worked well for all triazolium salts derived from the 1,4-regioisomer of the triazoles, for the methlyene-bridged bi-triazolium salt derived from a 1,5-substiuted triazole, we observed the unexpected decomposition of the bi-triazolium and the formation of a triazole-borane with a new NÀ B bond. All compounds were characterized via multinuclear NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction. Furthermore, the MIC-boranes were used as reducing agents for the reduction of the C=O of aldehydes to the corresponding alcohols.

Azide‐Substituted 1,2,3‐Triazolium Salts as Useful Synthetic Synthons: Access to Triazenyl Radicals and Staudinger Type Reactivity

“…After the reaction of L3 with 2 equivalents of PPh 3 , no distinct product could be observed. A possible explanation for the observation can be the unstable nature of the methylene bridge under the reaction conditions, which was also noted previously by us [29] …”

“…A possible explanation for the observation can be the unstable nature of the methylene bridge under the reaction conditions, which was also noted previously by us. [29] After having achieved the selective and successful reaction of L1 with PPh 3 , we were interested in further exploring the potential of this cationic azido-triazolium unit with a particular…”

Chemistry of Compounds Based on 1,2,3-Triazolylidene-Type Mesoionic Carbenes

“…Suprisingly, in the case of a methylene-bridged ditriazolium salt 129 , the ligand was seen to decompose, leading to the formation of a new type of triazole borane 148 containing a N–B bond ( Scheme 30 ). 126 …”

Cu-catalyzed cycloaddition of aryl azides to 1-iodobuta-1,3-diynes: an experimental and quantum chemical study of unusual regiochemistry

“…24 Additionally, several examples of the formation of 1,5-disubstituted triazoles from terminal alkynes using basic conditions have been reported. 25,26…”

“…24 Additionally, several examples of the formation of 1,5-disubstituted triazoles from terminal alkynes using basic conditions have been reported. 25,26 Reactions of various internal alkynes with azides using different catalytic systems have been comprehensively studied and reviewed recently. 27 1-Haloalkynes also react with azides under Cu(I) catalysis affording 5-halogen-1,4-disubstituted triazoles (Fig.…”