A rhodium(II)/rhodium(III) redox couple for C-H bond amination with alkylazides: a rhodium(III)-nitrenoid intermediate with a tetradentate [14]-macrocyclic ligand.

The catalytic activity of a rhodium(II) dimer complex, [Rh II (TMAA)] 2 (TMAA = tetramethyltetraaza[14]annulene), in C-H amination reactions with organic azides is explored. Organic azides (N 3 -R) with an electron-withdrawing group such as a sulfonyl group (trisylazide; R = S(O) 2 iPr3 C 6 H 2 (Trs)) and a simple alkyl group (R = (CH 2 ) 4 Ph, (CH 2 ) 2 OCH 2 Ph, CH 2 Ph, or C 6 H 4 NO 2 ) are employed in intra- and intermolecular C-H bond amination reactions. The spectroscopic analysis using ESI-mass and EPR spectroscopy techniques on the reaction intermediate generated from [Rh II (TMAA)] 2 and N 3 -R reveals that a rhodium(III)-nitrenoid species is an active oxidant in the C-H bond amination reaction. DFT calculations suggest that the species can feature a radical localised nitrogen atom. The DFT calculation studies also indicate that the amination reaction involves hydrogen atom abstraction from the organic substrate R'-H by the NR moiety of 2 N˙R and successive rebound of the generated organic radical intermediate R'˙ to [Rh III (NH-R)(TMAA)], giving [Rh II (TMAA)] and R'-NH-R (amination product).