Selective 3,3‐Rearrangement of Azobenzenes upon Complexation by a Frustrated Lewis Pair

Abstract

AbstractThe reaction of the oxygen‐bridged frustrated Lewis pairs (FLPs) tBu2P−O−Si(C2F5)3 (1) and tBu2P−O−AlBis2 (2) with azobenzene, promoted by UV irradiation, led to a selective complexation of the cis‐isomer. The addition product of 2 is stable, while the adduct of 1 isomerizes in solution in an ortho‐benzidine‐like [3,3]‐rearrangement by cleavage of the N−N bond, saturation of the nitrogen atoms with hydrogen atoms and formation of a new bond between two phenyl ortho‐carbon atoms. Similar rearrangements take place with different para‐substituted azobenzenes (R=Me, OMe, Cl) and di(2‐naphthyl)diazene, while ortho‐methylated azo compounds do not form adducts with 1. All adducts were characterized by multinuclear NMR spectroscopy and elemental analyses and the mechanism of the rearrangement was explored by quantum‐chemical calculations.