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

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 degreesC were found to be in excellent agreement and allowed for the determination of the Gibbs standard activation energy DeltaG(odouble dagger) for the diastereoisomerization of 1 as 70.4 kJ/mol. The rotational activation enthalpy DeltaH(double dagger) and the rotational activation entropy DeltaS(double dagger) 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 degreesC allowed the first separation of a stereolabile perisubstituted diarylnaphthalene into its syn- and anti-diastereoisomers, which interconvert at room temperature.