N-Heterocyclic Carbene-Stabilized Boranthrene as a Metal-Free Platform for the Activation of Small Molecules

Abstract

The multielectron reduction of small molecules (e.g., CO) is a key aspect of fuel synthesis from renewable electricity. Transition metals have been researched extensively in this role due to their intrinsic redox properties and reactivity, but more recently, strategies that forego transition metal ions for p-block elements have emerged. In this vein, we report an analogue of boranthrene (9,10-diboraanthracene) stabilized by N-heterocyclic carbenes and its one- and two-electron oxidized congeners. This platform exhibits reversible, two-electron redox chemistry at mild potentials and reacts with O, CO, and ethylene via formal [4+2] cycloaddition to the central diborabutadiene core. In an area traditionally dominated by transition metals, these results outline an approach for the redox activation of small molecules at mild potentials based on conjugated, light element scaffolds.

Selective CO2 Splitting by Doubly Reduced Aryl Boranes to Give CO and [CO3]2−

“…CO reduction under mild conditions,a lbeit not always in ac atalytic fashion. [14] In the meantime, related systems have been disclosed by Kinjo [15,16] and Harman [17] and shown to add CO 2 through one of its C=O bonds (D-F;S cheme 1b). Follow-up reactions with various reducing agents have been studied and the palette of obtainable compounds encompasses CO,H C(O)OH, H 3 COH, and CH 4 .…”

Engineering the Frontier Orbitals of a Diazadiborinine for Facile Activation of H2, NH3, and an Isonitrile

“…[6] Among them, only ahandful of boroncontaining heteroarenes have been shown to activate small molecules in reactions taking place at the boron centers under mild conditions ( Figure 1). [7][8][9][10] Theg roups of Wagner and Holthausen reported on the use of the dianionic 9,10diboraanthracene I for H 2 activation. [7] Harman and coworkers showed that the neutral N-heterocyclic carbene stabilized 9,10-diboraanthracene II undergoes [4+ +2] cycloaddition reactions with O 2 ,c arbon dioxide (CO 2 ), and ethylene.…”

“…[7] Harman and coworkers showed that the neutral N-heterocyclic carbene stabilized 9,10-diboraanthracene II undergoes [4+ +2] cycloaddition reactions with O 2 ,c arbon dioxide (CO 2 ), and ethylene. [8] Our group has demonstrated that 1,3,2,5-diazadiborinine III reacts with CO 2 ,c arbonyl compounds,a lkenes, and alkynes in af ormal [4+ +2] cycloaddition. [9] We have also isolated the annulated 1,4,2,5-diazadiborinine derivative IV, which not only reacts with non-activated unsaturated bonds, such as C = O, C = C, C C, and C Nb onds,b ut also cleaves C À O, B À H, Si À H, and P À Hbonds.…”

Phosphine‐NHC Manganese Hydrogenation Catalyst Exhibiting a Non‐Classical Metal‐Ligand Cooperative H2 Activation Mode

“…[13] Theresulting complex (4), showing methylation of the carbon atom linking the phosphine and NHC moieties, was isolated as am ixture of two diastereomers (ratio 6:1) differing by the position of the methyl group with respect to the iodine atom (Scheme 2, middle). Fort his purpose,c omplex 2 was first treated with KHMDS followed by the addition of an excess of classical alkylating agent such as MeI.…”