Boron and Hemilability
In 2011, we came across a class of boron-containing aldehydes that defied the fundamental teachings of organic chemistry: boron preferred to reside on carbon despite the well-recognized thermodynamic stability of the boron-oxygen bond. Since then, we have been searching for a mechanistic rationale behind this finding and developed a range of other boron-containing molecules that followed the logic of kinetic stabilization against decomposition pathways that normally plague compounds that contain C–B bonds.
This research avenue was started by Dr. Zhi He, who was a Ph.D. student in our lab in 2011. Concurrently, Prof. M. Burke of the UIUC developed a diastereoselective access to α-boryl aldehydes. Zhi unexpectedly passed away in 2017, which was a hard blow for all of us who knew him for his penetrating insights that led us to appreciate boron chemistry from a new perspective. There was no better tribute to Zhi than to dedicate our Nature Chemistry manuscript to his legacy. In this contribution, we report that boron can act as a chameleon, displaying high migratory aptitude in its tetracoordinate form in one setting, yet migrate as an electrophile under other conditions. Our main conclusion is that hemilability of the B–N bond plays the key role during migration. Encouraged by this discovery, we are currently seeking new reactions for the synthesis of hitherto inaccessible boron-based intermediates and endpoints of synthesis.