Promeet Saha

Flat, tri-coordinate boron rears its had, becomes tetra-coordinate and chiral! When treated in an appropriate manner, it forms enantiomers that are configurationally stable. Only since recently, boron-stereogenic complexes are accessible by catalytic enantioselective syntheses. What makes this particularly exciting is that tetra-coordinate boron compounds are considered promising light-emitting materials.

Abstract

Boron-based enantiomerism is fragile due to the inherent tendency of a dissociation of a ligand from tetra-coordinate chiral boron complexes under formation of the achiral tri-coordinate species. This review will present the different approaches in overcoming the inherent tendency of racemization in boron-stereogenic compounds. When embedded in an environment of chiral ligands or substituents, configurationally stable boron stereogenic centers can form in a diastereoselective manner. Compounds incorporating boron as the exclusive stereogenic center are obtained by resolution of the racemic mixtures. The recently developed – much more efficient – methods of a catalytic, enantioselective creation of boron stereogenic compounds are highlighted in this review. Finally the chiroptical properties of enantiomerically pure boron complexes that makes them promising materials or devices are addressed.

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Nature Chemistry, Published online: 16 March 2020; doi:10.1038/s41557-020-0430-7

Understanding the photophysical properties of transition-metal complexes is paramount to advances in photocatalysis, solar energy conversion and light-emitting diodes. Now, long-lived emission via thermally activated delayed fluorescence has been demonstrated from an air- and water-stable zirconium complex featuring excited states with significant ligand-to-metal charge transfer character.