<i>N</i>,<i>N</i>-Addition of Frustrated Lewis Pairs to Nitric Oxide: An Easy Entry to a Unique Family of Aminoxyl Radicals

The intramolecular cyclohexylene-bridged P/B frustrated Lewis pair [Mes₂PC₆H₁₀B­(C₆F₅)₂] <b>1b</b> reacts rapidly with NO to give the persistent FLP-NO aminoxyl radical <b>2b</b> formed by P/B addition to the nitrogen atom of NO. This species was fully characterized by X-ray diffraction, EPR and UV/vis spectroscopies, C,H,N elemental analysis, and DFT calculations. The reactive oxygen-centered radical <b>2b</b> undergoes a H-atom abstraction (HAA) reaction with 1,4-cyclohexadiene to give the diamagnetic FLP-NOH product <b>3b</b>. FLP-NO <b>2b</b> reacts with toluene at 70 °C in an HAA/radical capture sequence to give a 1:1 mixture of FLP-NOH <b>3b</b> and FLP-NOCH₂Ph <b>4b</b>, both characterized by X-ray diffraction. Structurally related FLPs [Mes₂PCHR¹CHR²B­(C₆F₅)₂] <b>1c</b>, <b>1d</b>, and <b>1e</b> react analogously with NO to give the respective persistent FLP-NO radicals <b>2c</b>, <b>2d</b>, and <b>2e</b>, respectively, which show similar HAA and O-functionalization reactions. The FLP-NOCHMePh <b>6b</b> derived from 1-bromoethylbenzene undergoes NOC bond cleavage at 120 °C with an activation energy of <i>E</i>_a = 35(2) kcal/mol. Species <b>6b</b> induces the controlled nitroxide-mediated radical polymerization (NMP) of styrene at 130 °C to give polystyrene with a polydispersity index of 1.3. The FLP-NO systems represent a new family of aminoxyl radicals that are easily available by <i>N</i>,<i>N</i>-cycloaddition of C₂-bridged intramolecular P/B frustrated Lewis pairs to nitric oxide