(Pyridyl)-Aminotriazoles as Versatile Synthetic Synthons: Amido Complexes, “Normal” Triazole-Based Imines and Metallo Mesoionic Imines

Mesoionic compounds are currently hugely popular in several fields such as organic chemistry, organometallic chemistry and homogeneous catalysis. A new class of mesoionic compounds are the mesoionic imines (MIIs). For MIIs based on a 1,2,3-triazole core, the synthetic strategy involves alkylation/arylation of the triazole-N3 atom and subsequent deprotonation to de-liver MIIs. We present here 5-amino-4-pyridyl-1,2,3-triazole as an alternative and versatile synthon for generating metallo-MIIs. In this approach, we make use of metallation at the N-pyridyl/N3-traizole chelating pocket (instead of quarternisation of N3-triazole) and subsequent deprotonation to generate highly versatile and tunable metallo-MIIs. These unprecedented metallo-MIIs contain a highly nucleophilic N-donor site, and a tunable electrophilic metal site within the same platform. Apart from displaying strong and directed H-bonding interactions like their “classical” MII analogues, the metallo-MIIs engage in aromatic C-F activation as well as meta-C-H activation reactions. Facile synthesis of homo and heterodincuelar complexes which contain a mixed coordinative saturation/unsaturation with these metallo-MICs is presented. Apart from the metallo-MICs we have also used 5-amino-4-pyridyl-1,2,3-triazole as a viable precursor to generate the first examples of amido-1,2,3-triazole complexes and the first example of a “normal” (and not mesoionic) 1,2,3-triazole based imine. Apart from a combination of synthetic chemistry, multinuclear NMR spectroscopy and single crystal X-ray diffraction, (TD)DFT calculations were also used to shed light on the electronic structure and the frontier orbital situation of these compounds. Our results thus establish metallo-MIIs as a versatile new class of mesoionic compounds that combine the modularity of click reactions, with the functionality of metal fragments to generate electronically ambivalent compounds with a huge potential in synthetic chemistry, catalysis and beyond.