Isolable Monocyclic <i>N</i> ‐Heterocyclic Radicals Supported by Rare‐Earth Organometallics

ABSTRACT Monocyclic N ‐heterocyclic radicals are the elementary reactive intermediates in synthetic chemistry and biochemical processes, but their isolation remains a central challenge due to extremely high reactivity. Here we report the first structurally characterized example of monocyclic pyridine radical supported by metal ions, [K(crypt‐222)][Cp* 2 RE(PyS 2‐• )] ( 2‐RE , PyS 2‐• = radical anion of pyridine‐2‐thiolate), and the first stable monocyclic triazine radical for any species, [K(crypt‐222)][(Cp* 2 RE) 3 (TrizS 4‐• )] ( 4‐RE , TrizS 4‐• = radical anion of 1,3,5‐triazine‐2,4,6‐tris(thiolate)), based on rare earth thiolate systems. Detailed structural, computational, UV–vis, and EPR data support the presence of heterocyclic radicals, which show a complicated, uneven spin density distribution at both pyridine and triazine rings. Remarkably, the unusual bonding characters between the lanthanide centers and the SOMO π*‐orbital of the radical promote strong ferromagnetic coupling from radical to lanthanide ions and achieve the largest gadolinium‐radical ferromagnetic coupling observed to date, J Gd–rad = +28.55(57) cm −1 ( Ĥ = ‐2 J Gd‐Rad Ŝ Gd · Ŝ Rad ) in 2‐Gd , while compound 4‐Dy exhibits slow magnetic relaxation. Furthermore, the initial exploration on reactivity revealed the potential ability of the pyridine radical to activate inert bonds. Those results contribute to a better understanding of highly reactive species involving monocyclic heterocyclic radicals.