Abstract
Free nitrenes of R–N are short-lived intermediates in a variety of nitrogen-involved transformations. They feature either a singlet ground state or a triplet ground state, depending on the electronic properties of the substituents R. Triplet arylnitrenes typically undergo facile ring expansion to azacycloheptatetraenes, making their isolation in the condensed phase highly challenging. Herein, we present the synthesis, isolation and characterization of an isolable triplet arylnitrene supported by a bulky hydrindacene ligand. The high stability is largely attributed to the sufficient steric hindrance and effective electron delocalization imparted by the supporting ligand. Electron paramagnetic resonance spectroscopy in conjunction with highly correlated wavefunction based ab initio calculations unambiguously demonstrated its triplet ground state with axial zero-field splitting D = 0.92 cm–1 and vanishing rhombicity E/D = 0.002. This work not only presents a long-sought reaction intermediate, but also provides in-depth insights into the reaction mechanisms involving nitrenes.