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

Abstract

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 rac5/rac6 ratio; the rac6 isomer predominated for amidoboronates based on pyrocatechol, ranging from a ratio of 0 : 1 with electron-withdrawing Cl substituents to 0.5 : 0.5 for electron-donating NMe2 substituents. 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 and the rac5 isomer was the major isomer following exchange.