The in Situ NHC-Palladium Catalyzed Selective Activation of B(3)–H or B(6)–H Bonds of o-Carboranes for Hydroboration of Alkynes: An Efficient Approach to Alkenyl-o-carboranes

Abstract

An in situ Pd-NHC catalyzed selective B­(3,6)-H activation for hydroboration of internal alkynes has been accomplished under mild conditions. This work offers a facile approach for the synthesis of alkenyl-o-carboranes and has important reference for selective functionalization of B­(3,6)–H bonds.

Facile Construction of New Hybrid Conjugation via Boron Cage Extension

“…Since the discovery of carboranes in the last century, their functionalization has been the central study in boron chemistry. In particular, the 3D cage structure of carboranes containing multiple B–H vertexes allows them to be substituted by various functional groups to construct B–C or B–X (X = heteroatoms) bonds. − In recent years, the fast development of B–H functionalization has offered an alternative and efficient pathway to synthesize the functionalized carborane derivatives. ,− However, it remains challenging to use these known synthetic schemes to readily access the aforementioned 2D–3D fused molecular systems as the following issues have to be addressed: (I) site-selective functionalization among the multiple B–H/C–H bonds; (II) realization of stepwise reactions in a one-pot manner; (III) the steric hindrance effect of 3D carborane; (IV) the side reactions associated with the B–H functionalization.…”

The transition metal-catalysed hydroboration reaction

“…11 Subsequent work improved activity for catalytic hydroborations of alkynes and alkenes involving polyhedral boranes and carboranes. 12–25 Hydroborations of alkynes and alkenes with borazine and related compounds have been studied in detail. 26–30 Due to prohibitive costs, reactions involving these boranes are generally not synthetically useful and thus will not be comprehensively covered in this review.…”

Pd-NHC catalysed regioselective activation of B(3,6)–H ofo-carborane – a synergy between experiment and theory

“…1 Therein, the palladium N-heterocyclic carbene (Pd-NHC) catalysed regioselective activation of o -carboranes is a promising approach for the preparation of electron-deficient B(3,6)-functionalized o -carboranes with high-efficacy. 2 As NHC ligands have strong σ-donating ability, high tunability, and are electron-rich, they effect the transfer of electrons to a bound transition metal atom, facilitating related coupling reactions. 3 Unlike the electrophilic Pd(OAc) 2 catalyst, the strong σ-donating ability of the NHC ligand weakens the electrophilicity of a bound Pd atom, inhibiting the electrophilic palladation of B(8,9,10,12)–H 4 and preferentially driving the electron-deficient B(3,6)–H activation of o -carboranes.…”