Highly selective palladium-catalyzed one-pot, five-fold B–H/C–H cross coupling of monocarboranes with alkenes

Abstract

Palladium-catalyzed five-fold B–H/C–H cross coupling of monocarboranes with alkenes enables the synthesis of selectively penta-functionalized boron clusters.

Variable Metal Chelation Modes and Activation Sequence in Pd-Catalyzed B–H Poly-arylation of Carboranes

“…This indicates that the Pd­(II) center prefers to activate the BH vertex with less steric hindrance caused by the aryl substitution in the previous stage. Here, our observation is distinct from the previously reported examples describing the consecutive activation of the neighboring B–H bonds when using mono-dentate acylamino or carboxylic acid DGs for the B–H arylation of o -carborane and mono-carborane anion. ,, We deduce that the steric bulk caused by the combination of bidentate DG and newly installed phenyl group(s) is responsible for this new activation sequence. In addition, the catalytic performance of the bicyclic model intermediate 3 has been examined (Scheme , eq 7).…”

“…Notable progresses in this direction include (i) electrophilic fluorination, acetoxylation, or sequential iodination/arylation of the electron-rich B­(8,9,10,12)–H bonds of o -carboranes and (ii) acylamino-directed B­(4,7,8)- and B­(5,8,9)-tri-arylation of o -carboranes (Scheme b). Related examples on the poly-substitution of monocarborane anion [CB 11 H 12 ] − including halogenation, alkylation, arylation, and alkenylation have also been reported (Scheme c) . Despite these advances on monocarborane anion and o -carborane, regioselective poly-substitution of m - and p -carboranes is yet to be explored.…”

Selective B(5,8,9)-Triarylation Reaction of o-Carboranes through Determination of the Order of Introduction of Aryl Groups into B(4)-Acylamino-o-carboranes

“…Thus, we wondered about the possibility of iterative B–H functionalization in a single operation on a mechanistic platform. Although iterative B–H alkylation, arylation, alkenylation, acetoxylation, and fluorination have been reported, these reactions are often nonselective and/or uncontrollable. Therefore, selective and controllable iterative B–H functionalization based on determination of the order of introduction of substituents into the BH vertices of carborane clusters continues to be a major challenge.…”

Highly selective electrophilic B(9)-amination of o-carborane driven by HOTf and HFIP

“…9 In the past decade, the main work for the selective functionalization of o -carborane focused on the transition-metal catalyzed B–H bond activation. 10–12 However, in most cases, it required introducing a directing group to realize reactivity and selectivity. 12 From the aspects of economic and environmental considerations, metal-free B–H functionalization without a directing group is more attractive.…”