Chiral ligand induced distortions: the origin of pyramidal three-coordinated lithium ions in the X-ray crystal structure of Lithium (1R,2R,4S)-exo- 2-[o-(dimethylaminomethyl)phenyl]-1,3,3-trimethylbicyclo[2.2.1]heptan-endo-2-olate

Abstract

The X-ray crystal structure of dimeric lithium (1R,2R,4S)-exo-2-[o-(dimethylaminomethyl)phenyl]-1,3,3-trimethylbicyclo[2.2.1]heptan-endo-2-olate (2-Li)₂ exhibits lithium ions with pyramidal environments of oxygen and nitrogen atoms. Ab initio (RHF/6-31+G*) computations of dimeric trimethylamine-coordinated lithium methoxide show that electrostatics disfavour the pyramidal distortions at lithiums in (2-Li)₂ by 5.0 kJ/mol. ONIOM(B3LYP/6-31+G*:UFF) computations of (2-Li)₂ as well as of (2-Li-b)₂ and (2-Li-c)₂, with one or two planar constrained lithium ion environments, reveal destabilizations of 32.2 and 97.5 kJ/mol, respectively, upon planarization at lithium. The destabilizations of planar coordinated lithiums in (2-Li-b)₂ and (2-Li-c)₂ arise from repulsions between methylamino groups and bicycloheptane moieties and give rise to the observed pyramidal environments at the lithiums in the X-ray crystal structure of (2-Li)₂.