The Dynamic Covalent Chemistry of Amidoboronates: Tuning the rac5/rac6 Ratio via the B-N and B-O Dynamic Covalent Bonds

Amidoboronates were prepared as a mixture of up to three isomers (rac5, meso5 and rac6) from the reductive coupling of N-aryl iminoboronates with either cobaltocene or decamethylcobaltocene in acetonitrile. The interconversion of rac5 and rac6 isomers via rearrangement of their dynamic covalent B N bonds was investigated in solution by redissolving isolated crystals. The aniline para substituent and catechol within the amidoboronates tuned the distribution between the rac5 and rac6 isomers; the rac6 isomer predominated for amidoboronates based on pyrocatechol with electron-withdrawing substituents and no interconversion was observed for the rac5 isomers of amidoboronates based on tetrachlorocatechol. Furthermore, the rac5/rac6 distribution was altered by catechol exchange of pyrocatechol for tetrachlorocatechol exploiting the dynamic covalent B O bonds.