Chiral bis(mandelato)borate salts for resolution via metathesis crystallization.

Abstract

Spiroborate anions have potential for crystallization or resolution and chiral bis(mandelato)borate anions can be used for the efficient resolution of a diverse range of racemic cations via diastereomeric salt formation. The syntheses, X-ray crystal structures and solubilities of three chiral bis(mandelato)borate salts, namely poly[[aqua-μ3-bis[(R)-mandelato]borato-lithium(I)] monohydrate], [Li(C16H12BO6)(H2O)]n or Li[B(R-Man)2]·H2O, (1), ammonium bis[(R)-mandelato]borate, NH4+·C16H12BO6- or NH4[B(R-Man)2], (2), and tetra-n-butylammonium bis[(R)-mandelato]borate, C16H36N+·C16H12BO6- or NBu4[B(R-Man)2], (3), are reported. They all have a BS configuration and show a reasonably well-conserved anion geometry. The main conformational variation is the orientation of the two phenyl groups, supporting the idea that [B(Man)2]- is a semi-rigid anion. The salts are differentially soluble in a range of solvents, meaning they could be useful as reagents for resolution via a metathesis crystallization approach.