Benzoin condensation of aromatic aldehydes catalyzed by N-heterocyclic carbenes under mild conditions

Abstract

The benzoin condensation was used to evaluate the catalytic activity of different N-heterocyclic carbenes as a function of their structure and N-substituents. There is a correlation between the length of an N-alkyl substituent and its performance as an organocatalyst. Heteroaromatic aldehydes were found to be the most reactive, among the screened substrates, finishing the reaction in 30 minutes, with almost quantitative yields. On the other hand, p-nitrobenzaldehyde, a strongly electrophilic aldehyde, was the least reactive. Electronic effects have little influence on the reaction yield but steric effects can dramatically reduce it. The preformed organocatalyst reacts faster than the generated in situ, with minimum solvent.

Mechanistic and multiscale aspects of thermo-catalytic CO2conversion to C1products

“… 98,259,269–275 In particular, Cu/ZnO/ZrO 2 showed very high activity and selectivity at low temperatures (180–240 °C). 276–279 This is likely due to the weak hydrophilic nature of ZrO 2 , which may inhibit the poisoning effect of water on the active sites 272,273 and promote the activity by increasing Cu dispersion, which can strongly affect CO 2 adsorption and methanol selectivity. 280,281 Other materials investigated for CO 2 hydrogenation to methanol are Au/CeO x /TiO 2 , 282 In 2 O 3 , 283–287 Ir–In 2 O 3 , 288 Ni–In 2 O 3 , 289 Mn–Co, 290 Ni–Ga, 291 ZnO–ZrO 2 , 292 GaPd 2 , 293 and Co/SiO 2 .…”

Photocatalytic CO2 Reduction Using an Iron–Bipyridyl Complex Supported by Two Phosphines for Improving Catalyst Durability

“…BIH was synthesized according to modified literature procedures . A 300 mL flask equipped with a magnetic stir bar was charged with 2-phenylbenzimidazole (11.65 g, 60 mmol) and dehydrated THF (180 mL).…”