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 (rac(5), meso(5) and rac(6)) from the reductive coupling of N-aryl iminoboronates with either cobaltocene or decamethylcobaltocene in acetonitrile. The interconversion of rac(5) and rac(6) 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 rac(5)/rac(6) ratio; the rac(6) 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 rac(5) isomers of amidoboronates based on tetrachlorocatechol. Furthermore, the rac(5)/rac(6) distribution was altered by catechol exchange of pyrocatechol for tetrachlorocatechol exploiting the dynamic covalent B-O bonds and the rac(5) isomer was the major isomer following exchange.

Automated summary

Amidoboronates were synthesized as a mixture of up to three isomers through reductive coupling of N-aryl iminoboronates with cobaltocene or decamethylcobaltocene in acetonitrile. The interconversion between rac(5) and rac(6) isomers was studied, with the rac(6) isomer predominating when based on pyrocatechol. Catechol exchange altered the rac(5)/rac(6) distribution, with the rac(5) isomer becoming the major isomer following exchange.