Tris(1-naphthyl)- and tris(2-naphthyl)methyl cations: highly crowded triarylmethyl cations1

Abstract

The highly hindered tris(1-naphthyl)methyl and tris(2-naphthyl)methyl cations 3 and 5 have been prepared under long lived stable ion conditions and characterized by ¹³C NMR spectroscopy at low temperatures. The latter can abstract hydride from cycloheptatriene to afford tris(2-naphthyl)methane 7, but the reaction of cycloheptatriene with the more crowded cation 3 failed to give the corresponding hydrocarbon. A primary kinetic isotope effect, k_H/k_D = 7.1 ± 0.5, found in the former case supports a colinear hydride abstraction mechanism. The ions 3 and 5 upon quenching rearranged to give a mixture of isomeric 13-(1-naphthyl)-1,2,7,8-dibenzofluorene 4 and 13-(2-naphthyl)-2,3,6,7-dibenzofluorene 6, respectively.