Metal‐Free Oxidative B−N Coupling of nido‐Carborane with N‐Heterocycles

Abstract

Ag eneral method for the oxidative substitution of nido-carborane (7,8-C 2 B 9 H 12 À )w ith N-heterocycles has been developed by using 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as an oxidant. This metal-free B À Ncoupling strategy, in both inter-a nd intramolecular fashions,g ave rise to aw ide arrayo fc harge-compensated, boron-substituted nido-carboranes in high yields (up to 97 %) with excellent functional-group tolerance under mild reaction conditions.T he reaction mechanism was investigated by density-functional theory (DFT) calculations.Asuccessive single-electron transfer (SET), BÀH hydrogen-atom transfer (HAT), and nucleophilic attackp athway is proposed. This method provides an ew approach to nitrogen-containing carboranes with potential applications in medicine and materials.

Electrooxidative B−H Functionalization of nido‐Carboranes

“…This situation is similar to ethers, implying the effect of the nucleophilicity of heteroatom on the reaction. However, N‐heterocycles reacted very well with nido ‐carboranes under the same electrooxidative conditions to give the same high yields of products 70 – 87 (see Scheme S1 in the Supporting Information) as by oxidative coupling when DDQ was used as an oxidant in our previous work [12] …”

“…According to our previous study using DDQ as the oxidant [12] and literature reports, [22] as well as in combination of the deuterium labelling experiment and cyclic voltammetry measurements, a plausible mechanism for the electrooxidative B−S bond formation between nido ‐carborane and diethyl sulfide was proposed in Figure 4. nido ‐Carborane is oxidized by anode through two single electron transfer processes to afford a cationic intermediate II.…”

Electrooxidative B−H Functionalization of nido‐Carboranes

“…In this regard, our group reported the replacement of FeCl 3 by an organic oxidant (DDQ) in the oxidative B−N coupling of nido ‐carboranes with N‐heterocycles (Figure 1 a). [12] The transition metal free reaction protocol ensured a high site selectivity and good functional group tolerance. In fact, little was known for the catalytic cage B‐H functionalization of nido ‐carboranes with organic compounds [13] .…”