Unraveling origin of chemoselectivity and regioselectivity of iridium‐catalyzed B(4)–H functionalization of o‐carborane by alkyne

• Published in: Journal of physical organic chemistry Vol. 36; no. 2
• Main Authors: Chen, Zitong, Liu, Jiying, Liu, Jiabin, Bao, Panpan, He, Hailing, Xia, Hui, Zhang, Wenjing
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.02.2023
• Subjects: alkenylation; Alkynes; Carborane; Chemical reactions; Decarboxylation; density functional theory; formal [4 + 2] annulation; functionalization of o‐carborane; Iridium; Protonation; Regioselectivity
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.4430

Functionalization at target site is an extremely challenging subject for surface modification of o‐carborane. It is a common tactic to introduce a directing group onto the C(2)–H vertex to induce exclusive B(4,5)–H functionalizations. In this study, was investigated. The computational results indicate that the formal [4 + 2] annulation going via the reductive elimination mechanism has kinetic priority than alkenylation via the decarboxylation mechanism. This is in excellent agreement with the experimental results of carborano‐isocoumarin as the major product. Given the alkyne insertion product, the protonation of alkene is likely to occur before decarboxylation followed by protonation of carborane. The reductive elimination of HOPiv is the regioselectivity determining step, and the non‐covalent interaction analysis discloses that it is the steric repulsion of the methyl on C(1) atom of carborane towards the iridacycle and the Cp* group that causes the higher barrier for the B(3)–H activation, which finally leads to the specific B(4)–H functionalization. Chemoselectivity and regioselectivity of Ir‐catalyzed functionalization of B(4)–H in o‐carborane have been unraveled through DFT calculations. The results are of significant theoretical guidance to developing new strategies for selective surface modification of carboranes.