Investigation of the Stereodynamics of Axially Chiral 1,8-Bis(2,2‘-diphenyl-4,4‘-dipyridyl)naphthalene and Cryogenic Separation of Its syn/anti-Isomers

Abstract

The kinetics of the syn/anti-isomerization of 1,8-bis(2,2‘-diphenyl-4,4‘-dipyridyl)naphthalene, 1, was investigated over a wide temperature range using variable-temperature NMR spectroscopy in conjunction with dynamic HPLC and computer simulation. Rate constants obtained utilizing both methods between −65.0 and 40.3 °C were found to be in excellent agreement and allowed for the determination of the Gibbs standard activation energy ΔG°⧧ for the diastereoisomerization of 1 as 70.4 kJ/mol. The rotational activation enthalpy ΔH⧧ and the rotational activation entropy ΔS⧧ were calculated from the Eyring plot as 57.5 kJ/mol and −43.4 J/K mol, respectively. Cryogenic chromatography using an achiral HPLC column at −70 °C allowed the first separation of a stereolabile perisubstituted diarylnaphthalene into its syn- and anti-diastereoisomers, which interconvert at room temperature.