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

Abstract

A general method for the oxidative substitution of nido‐carborane (7,8‐C2B9H12−) with N‐heterocycles has been developed by using 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) as an oxidant. This metal‐free B−N coupling strategy, in both inter‐ and intramolecular fashions, gave rise to a wide array of charge‐compensated, boron‐substituted nido‐carboranes in high yields (up to 97 %) with excellent functional‐group tolerance under mild reaction conditions. The reaction mechanism was investigated by density‐functional theory (DFT) calculations. A successive single‐electron transfer (SET), B−H hydrogen‐atom transfer (HAT), and nucleophilic attack pathway is proposed. This method provides a new approach to nitrogen‐containing carboranes with potential applications in medicine and materials.

Electrooxidative B−H Functionalization of nido‐Carboranes

“…Slightly decreased yields were observed when dibenzyl sulfide or bis(furan-2-ylmethyl)-sulfane was employed as the substrate (10,15). Cyclic thiothers were also reactive in the B-S bond formation (11)(12)(13)(14)16). Importantly, [b] NMe 4 OH solution 32 13 [c] NMe NH and carbonyl groups remained untouched in the formed products (13,14,16).…”

“…In this regard, our group reported the replacement of FeCl 3 by an organic oxidant (DDQ) in the oxidative B À Nc oupling of nido-carboranes with N-heterocycles (Figure 1a). [12] Thet ransition metal free reaction protocol ensured ah igh site selectivity and good functional group tolerance.I nf act, little was known for the catalytic cage B-H functionalization of nido-carboranes with organic compounds. [13] Therefore,w ec ontinue the synthetic exploration of nido-carboranes and wish to reach the following goals: ( 1) to find an environmentally friendly approach;…”

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.…”

A comparison of the catalytic efficiency of copper-based bimetallic nanoparticles in the click reactions

“…Triazoles, as a type of significantly useful N -heterocycles, 1–5 have been widely applied in fluorescent materials, drug discovery, chemosensing, biochemistry, dendrimers, agricultural products, materials science, corrosion-retarding agents, dyes, and polymer chemistry, 6–8 due to the physically and chemically inertness against reduction, oxidation and hydrolysis under basic or acidic conditions. 9 Plenty of methods have been developed for the synthesis of 1,2,3-triazoles.…”