Electronic Effect-Guided, Palladium-Catalyzed Regioselective B–H Activation and Multistep Diarylation of o-Carboranes with Aryl Iodides

Abstract

Density functional theory calculations at IDSCRF-B3LYP/DZVP computational level were conducted on palladium-catalyzed regioselective B–H activation and diarylation of o -carboranes with aryl iodides in solution. Computational results indicate that this reaction follows a multistep mechanism and needs to get over several transition states before the final B(4,5)-diarylated o -carborane derivatives are formed. B–H activation, oxidation addition, and successive reduction of the Pd(II) catalyst involving a Pd(II)–Pd(IV)–Pd(II) catalytic cycle has been confirmed, in which AgOAc plays a crucial role. Electron-donating group on the cage carbon of o -carboranes is verified to be beneficial for its B–H activation and diarylation, while steric hindrance between the aryl and o -carboranyl groups retards it. Natural population analysis and Gibbs free energetic results predict consistent regioselectivities with experiments and manifest the pivotal role of electronic effect in controlling regioselective B–H activation of o -carboranes. These results are expected to shed some light on further improvement of experimental conditions and better controlling of regioselectivities.

Regioselectivity of Pd-catalyzedo-carborane arylation: a theoretical view

“…[49][50][51][52][53][54][55][56] Usually, introducing a directing group (DG) on o-carborane is a powerful way to manipulate the regioselectivities of these B-H bonds. 27,47,[57][58][59][60][61] In 2014, Xie reported a catalytic B(4)-H alkylation of carboxylic o-carboranes using Cp*IrCl 2 as catalyst. 62 Later, Yan and Lu developed a B(3)-H acetoxylation of pyridyl-modified o-carborane using Cp*RhCl 2 (Scheme 1(b)).…”

Computational Investigation of Nickel-Mediated B–H Activation and Regioselective Cage B–C(sp2) Coupling of o-Carborane

“…On the other hand, affected by many factors such as large size of o-carboranyl group, many electrons involved in transition metals, and diverse regioselectivities of o-carborane's B-H activation, it is really challenging in computational cost to conduct theoretical studies on transition metal catalyzed regioselective B-H activation of o-carborane. Our group has recently conducted a computational study on palladium-catalyzed regioselective B-H activation and diarylation of o-carboranes with aryl iodides in solution, and found that the substituents on o-carborane have a significant effect on the regioselectivity of B-H activation [27]. In contrast to this, the presence of a fused five-membered ring in intermediates M2 and M3 (Scheme 1) here would Catalysts 2019, 9,548 3 of 16 affect the regioselectivity of B-H activation significantly, and lead to different diastereoselectivities in the following cage B-C(sp 2 ) coupling through direct B-H activation of o-carborane.…”