The Reactivity of Isomeric Nitrenium Lewis Acids with Phosphines, Carbenes, and Phosphide

Alkylation of spiro[fluorene‐9,3’‐indazole] at N(1) and N(2) with tBuCl affords the nitrenium cations [C(6)H(4)N(2)(tBu)C(C(12)H(8))][BF(4)], 1 and 2, respectively. Compound 1 converts to 2 over the temperature range 303–323 K with a free energy barrier of 28±5 kcal mol(−1). Reaction of 1 with PMe(3) afforded the N‐bound phosphine adduct [C(6)H(4)N(tBu)N(PMe(3))C(C(12)H(8))]BF(4)] 3. However, phosphines attack 2 at the para‐carbon atom of the aryl group with concurrent cleavage of N(2)−C(1) bond and proton migration to C(1) affording [(R(3)P)C(6)H(3)NN(tBu)CH(C(12)H(8))][BF(4)] (R=Me 4, nBu 5). Analogous reactions of 1 and 2 with the carbene SIMes prompt attack at the para‐carbon with concurrent loss of H(.) affording the radical cation salts [(SIMes)C(6)H(3)N(tBu)NC(C(12)H(8))(.)][BF(4)] 6 and [(SIMes)C(6)H(3)NN(tBu)C(C(12)H(8))(.)][BF(4)] 7, whereas reaction of 2 with BAC gives the Lewis acid‐base adduct, [C(6)H(4)N(BAC)N(tBu)C(C(12)H(8))][BF(4)] 8. Finally, reactions of 1 and 2 with KPPh(2) result in electron transfer affording (PPh(2))(2) and the persistent radicals C(6)H(4)N(tBu)NC(C(12)H(8))(.) and C(6)H(4)NN(tBu)C(C(12)H(8))(.). The detailed reaction mechanisms are also explored by extensive DFT calculations.