Post-Assembly Reactivity of N-Aryl Iminoboronates: Reversible Radical Coupling and Unusual B−N Dynamic Covalent Chemistry

Abstract

Post-assembly reaction of a dynamic covalent iminoboronate system following addition of Cp2Co resulted in the formation of a series of new reductively coupled dianionic dimers via C−C bond formation. The dimers formed as a mixture of BN-containing isomeric products: diastereomers rac5 and meso5, with coupled five-membered rings, and enantiomeric rac6, with a fused six-membered ring bicyclic system from C−C bond formation and rearrangement of the B−N bonds. Each isomer was identified using 1H NMR spectroscopy in combination with single crystal X-ray structure determination. Interestingly, interconversion between the coupled five-membered rings (rac5) and fused bicyclic systems (rac6) was found to occur through an unprecedented breaking and reforming of the B−N covalent bond. Further, the coupled products could be converted quantitatively back to their iminoboronate precursors with addition of the electron abstractor Ph3C+.