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

Evan N Keyzer; Alexandru Sava; Tanya K Ronson; Jonathan R Nitschke; Anna J McConnell

doi:10.1002/chem.201802790

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

Chemistry. 2018 Aug 14;24(46):12000-12005. doi: 10.1002/chem.201802790. Epub 2018 Jul 25.

Authors

Evan N Keyzer¹, Alexandru Sava¹, Tanya K Ronson¹, Jonathan R Nitschke¹, Anna J McConnell^{1

2}

Affiliations

¹ Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge, CB2 1EW, UK.
² Otto Diels Institute of Organic Chemistry, University of Kiel, 24118, Kiel, Germany.

Abstract

Post-assembly reaction of a dynamic covalent iminoboronate system following addition of Cp₂ Co 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 meso_5, with coupled five-membered rings, and enantiomeric rac_6, 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 ¹ H 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 Ph₃ C⁺ .

Keywords: dynamic covalent chemistry; iminoboronate; post-assembly; radical coupling; supramolecular chemistry.