Improved Synthesis of Icosahedral Carboranes Containing Exohedral B–c and C–c Bonds

We report improved methods utilizing orthogonal chemistry to achieve efficient substitution at electron-rich B-vertices and electron-poor C-vertices of carborane. Functionalization of B-vertices with alkyl and (hetero)aryl groups using corresponding Grignard reagents has been improved by the use of a Pd-based precatalyst featuring an electron-rich biaryl phosphine ligand. Using the developed catalytic conditions lead to cross-coupling transformations achieved within several hours. Importantly, this method is applicable towards alkyl-based Grignard reagents containing β-hydrogens. Additionally, transition metal-free substitution of (hetero)aryl substrates on C-vertices was developed under S_NAr conditions. The selective substitution of carboranes afforded by these methods holds potential for the rational synthesis of heterofunctionalized boron clusters with substituents on both boron and carbon-based vertices.