Triimidazo[1,2-a:1’,2’-c:1’’,5’’-e]triazine: a new Scaffold for Catalytically Active NHC-Protected Gold Nanoparticles

N-heterocyclic carbenes (NHC) are a new trend in the stabilization of metal nanoparticles. In this work, we studied a cyclic triimidazole obtained by thermal decomposition in high vacuum of a copper-diimidazolate polymer[1]. The [1,2-a:1’,2’-c:1’’,2’’-e] isomer is the most studied while the [1,2-a:1’,2’-c:1’’,5’’-e] one (1) did not collect any interest. Recently, we pointed our attention on the reactivity of 1 due to the presence of an imidazole ring suitable for the generation of Arduengo carbenes[2]. Treating 1 with benzylbromide led to the isolation of single crystals of an imidazolium salt (2) with bromine as counterion, characterized by SCXRD. Further ionic exchange with tetrachloroaurate anions and the subsequential reduction of the obtained salts led to the formation of stable NHC protected gold nanoparticles (NHC@AuNPs). NHC@AuNPs have been characterized via different techniques such as XRPD, FT-IR, TEM, and UV-Vis absorption, revealing the presence of spheric nanoparticles with a mean diameter below 10 nm. As synthesized nanoparticles have been deposited on different supports and tested as recoverable catalysts in nitro-group reduction with sodium borohydride on simple aromatic molecules such as nitrobenzene, showing high conversion and yield. [1] D. Schubert et al., Crystal Growth and Design 2011, 11, 843-850 [2] D. Buck, D. Kunz, Organometallics 2015, 34, 5335-5340