Ambident reactivity of aryloxide ions towards 1,3,5-trinitrobenzene, low-temperature characterization of the elusive oxygen-bonded σ-complexes by 1H and 13C NMR spectroscopy

The ambident reactivity of phenoxide ion towards 1,3,5-trinitrobenzene (TNB) was re-examined by means of a novel reaction system(CD3CN–glyme-d10) which allows the investigation of species formed at low temperatures (−40°C), contrasting with previous studies in dimethyl sulfoxide (DMSO) at ambient temperature. The new method coupled with 400 MHz NMR spectroscopy has allowed the definitive observation of both O- and C-bonded phenoxide σ-complex adducts for the first time, confirming the formation of the former through kinetic control and of the latter through thermodynamic control. The corresponding O-bonded σ-adduct in the TNB–mesitoxide system (whereC-bonded σ-adduct formation is not possible but where there is competing nitro group displacement) has also been characterized by 1H and 13C NBR. Another O-bonded aryloxide adduct characterized is that from the reaction of TNB with3,5-di-tert-butylphenoxide; in this system there is also competing NO2 displacement. Stereoelectronic factors in the O-bonded σ-adducts and aryl ethers are discussed.