Expanding the Scope of Palladium-Catalyzed B–N Cross-Coupling Chemistry in Carboranes

Abstract

Over the past several years, a number of strategies for the functionalization of dicarba-closo-dodecaboranes (carboranes) have emerged. Despite these developments, B-N bond formation on the carborane scaffold remains a challenge due to the propensity of strong nucleophiles to partially deboronate the parent closo-carborane cluster into the corresponding nido form. Here we show that azide, sulfonamide, cyanate, and phosphoramidate nucleophiles can be straightforwardly cross-coupled onto the B(9) vertices of the o-and m-carborane core from readily accessible precursors without significant deboronation by-products, laying the groundwork for further study into the utility and properties of these new B-aminated carborane species. We further showcase select reactivity of the installed functional groups highlighting some unique features stemming from the combination of the electron-donating B(9) position and the large steric profile of the B-connected carborane substituent.

Facile Attachment of Halides and Pseudohalides to Dodecaborate(2-) via Pd-catalyzed Cross-Coupling

“…The azide obtained here for the first time invites one to perform click chemistry. While this has been described for carboranyl azides [ 30 ], such reactions have not yet been described for the dodecaborate cluster. As a prototype reaction, we used acetylene dimethylcarboxylate.…”

“…The bromide and the chloride did not react; we had already observed this for cross-coupling reactions with amides and anilines [ 16 ]. This is in contrast to carboranes, where the bromide can undergo reactions to the isocyanate and azide, and to the amides [ 30 ].…”

Synthesis of {CB11} Monocarborane Sulfonamides by B2‐Selective Rhodium‐Catalyzed B−H Activation

“…[47][48][49][50][51][52][53][54][55][56][57] When it comes to the formation of BÀ N bonds specifically, early work comprised direct cage amination under strongly reducing conditions, the use of an electrophilic nitrogen source or cross coupling of halogenated clusters. [40,41,[58][59][60][61][62][63][64][65][66][67] The first BÀ H activation approach was published in 2016 by the Xie group and involved Ir(III)-catalyzed {C 2 B 10 } amination and sulfonamidation (Figure 2,a -i). [68] Similar sulfonamidation results were reported in 2017 by Bregadze, Lu and Yan.…”

Synthesis and Crystal Structure of 9,12-Dibromo-ortho-Carborane

“…Despite the fact that the bromination of carboranes was first described as early as the mid-1960s [44], the chemistry of bromo derivatives of carboranes has been studied to a much lesser extent compared to the iodo derivatives. Nevertheless, recently there has been an increase in interest in bromo derivatives of carboranes due to their use in cross-coupling reactions [45][46][47][48] and the study of intermolecular interactions with the formation of hydrogen and halogen bonds [49].…”