Palladium Catalyzed Selective B(3)–H Activation/Oxidative Dehydrogenative Coupling for the Synthesis of Bis(o-carborane)s

Abstract

A palladium catalyzed selective B(3)–H activation/oxidative dehydrogenative coupling for the synthesis of bis­(o-carborane)­s connected with B(3)–B(3′) and B(3)–B(6′) bonds has been developed for the first time. A plausible mechanism involving stepwise activation of B(3)–H and B­(3′/6′)–H bonds by PdII and PdIV was proposed. This work is the first example and the most efficient protocol for synthesis of bis­(o-carborane)­s connected with B(3)–B(3′) and B(3)–B(6′) bonds, which has important reference for design, synthesis, and application of bis­(o-carborane)­s in related fields.

Iridium Catalyzed Selective Arylation of B(3)‐H Bond of o‐Carborane via B−H/C−H Activation

“…Recently, with pyridyl as a directing group, the palladium catalyzed selective B(3)‐H activation/oxidative dehydrogenative coupling for the synthesis of bis( o ‐carborane)s have been developed in our group [8] . This result demonstrates the selective activation of B(3,6)‐H bonds and following dehydrogenative coupling with C(sp 2 )−H bond would be a feasible strategy for arylation of o ‐carboranes.…”

Advances in the Synthesis of Biscarboranes

“…Recently, this strategy was further extend to construction of bis(o-carborane)s linked with B3À B3' and B3À B6' bonds in Cao's group. [22] With pyridyl as directing group, the B(3)À H with electron deficient characteristic could be activated by Pd- halogen, aryl, furan and thiophene were all compatible with this coupling well and generated the bis(o-carborane)s linked with B3-B3' and B3-B6' bonds with moderate to good yields. Likewise, both isomers could be separated by column chromatography, and a plausible mechanism involving pyridine directed Pd II /Pd IV -catalyzed dual B(3)À H activation was proposed (Scheme 11).…”

Electrochemical Cage Activation of Carboranes

“…[30] However, most of the established oxidation reactions require noble transition metal catalysts and an excess amount of chemical oxidants, which compromises the resource economy. [13,14] In sharp contrast, the combination of base-metal catalysis and electrochemistry for the BÀ H functionalization of carboranes represents an attractive and environmentally friendly alternative to traditional methods, and avoids the use of harsh oxidizing agents and noble transition metal catalysts (Scheme 7).…”

“…Despite indisputable advances in the cage activation of carboranes, [6,10,11] oxidative carborane cage functionalizations [12] unfortunately often suffer from the need for stoichiometric amounts of toxic and/or expensive chemical oxidants, such as copper(II) [13] or silver(I) salts, [14] thus limiting the inherently sustainable nature and generality of the cage activation approach. The direct exploitation of electric current for the development of new redox strategies in synthetic organic transformations is on the verge of a renaissance by virtue of its sustainability, resource economy, and inherent safety.…”