C–H Borylation by Platinum Catalysis

Abstract

Herein, we describe the platinum-catalyzed borylation of aromatic CH bonds. N-Heterocyclic carbene-ligated platinum catalysts are found to be efficient catalysts for the borylation of aromatic C(sp 2 )H bonds when bis(pinacolato)diboron is used as the boron source. The most remarkable feature of these Pt catalysts is their lack of sensitivity towards the degree of steric hindrance around the CH bonds undergoing the borylation reaction. These Pt catalysts allow for the synthesis of sterically congested 2,6-disubstituted phenylboronic esters, which are otherwise difficult to synthesize using existing CH borylation methods. Furthermore, platinum catalysis allows for the siteselective borylation of the CH bonds ortho to fluorine substituents in fluoroarene systems. Preliminary mechanistic studies and work towards the synthetic application of this platinum catalyzed CH borylation process are described.

N-Heterocyclic Carbene Complexes in C–H Activation Reactions

“…Mechanistically, the authors demonstrated that dvtms dissociates from the metal center (Scheme 88). 198 It was proposed that the coordinatively unsaturated Pt−NHC complex reacts with B 2 pin 2 to give [Pt(NHC)(Bpin) 2 ], followed by C(sp 2 )−H activation via σ-bond metathesis or oxidative addition to give Pt(IV).…”

Reversible carbon–boron bond formation at platinum centers through σ-BH complexes

“…Although most of this type of C–H borylation processes have been carried out using rhodium and iridium systems, 4 there have been a few reports on the utilization of platinum complexes for the formation of C–B bonds, either in stoichiometric reactions or in catalytic processes. 5 Turculet and Stradiotto reported the dehydrogenative coupling of B–H/C–H bonds at a Pt( ii ) center, 5 a whereas Chatani, Tobisu et al suggested the participation of σ-BH complexes in the platinum-catalyzed borylation of arenes. 5 b , c However, the interaction of tricoordinated hydroboranes with platinum centers leading to σ-BH complexes has proven elusive.…”

Acenaphthene-Based N-Heterocyclic Carbene Metal Complexes: Synthesis and Application in Catalysis

“…N-Heterocyclic carbene complexes of copper and platinum possessing an acenaphthylene backbone subunit have been marginally reported to date [53,70,97], but have found catalytic applications.…”

“…Literature reports on NHC-BIAN-Pt complexes cover only a single example. In 2016, Tobisu and co-workers [97] published a synthesis of the platinum N-heterocyclic carbene complex 113 by the reaction of NHC precursor 4g with Karstedt's complex, yielding complex 113 in 36% yield (Scheme 45). The authors reported high catalytic activity of platinum complex 113 in the C-H activation/borylation reaction of 1,3-dimethyl-5-tertbutylbenzene (112), affording arylboronic ester 40b in 72% yield.…”