Lewis Base Promoted Reduction of CO₂ with BH₃NH₃ into Boryl Formates: CO₂ as a Carbon Source in Organic Synthesis Under Mild Conditions

Abstract

Lewis base promoted selective reduction of CO2 into boryl formates by using BH3NH3 as a reductant under mild conditions has been reported. The boryl formates, generated in situ, were shown to be reactive and versatile sources of formyl compounds to create new C–N, C–O, and C–C bonds. The reactivity of the boryl formates to yield formic acid, formamides, formates, secondary alcohols, and benzoheterocyclic rings was investigated.

Catalyst-free reductive cyclization of bis(2-aminophenyl) disulfide with CO2 in the presence of BH3NH3 to synthesize 2-unsubstituted benzothiazole derivatives

“…Therefore, high temperatures and high pressures are needed in the reaction. With hydrosilanes as the reductant, 2-unsubstituted benzothiazole can be obtained from the reaction of CO 2 and 2-aminothiophenol catalyzed by 1,5-diazabicyclo [4.3.0] non-5-ene (DBN), 19 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD), 20 acetate-based ionic liquids [Bmim][OAc] 21 or biomass-derived γ-valerolactone. 22 …”

Ammonia borane as a reducing agent in organic synthesis

“…An example of carbon dioxide reduction with AB promoted by a base was published by Xi and co-workers. 46 One equivalent of AB was reacted with one equivalent of base under CO 2 atmosphere (1 atm) using acetonitrile as solvent, at 80 °C for 12 hours. Using either triethylamine (Et 3 N) or 1,5,7triazabicyclo[4.4.0]dec-5-ene (TBD) as base, it was possible to form boryl formates (species in the box in Scheme 29), which were studied by 1 H and 11 B NMR.…”

Reduction of Carbon Dioxide with Ammonia-Borane under Ambient Conditions: Maneuvering a Catalytic Way

“…According to this proposal, ammonia-borane (NH 3 BH 3 ) can be utilized to reduce CO 2 catalytically under ambient conditions (313.15 K, 1 bar of CO 2 ) to formic acid with pincer-type phosphorus-based bifunctional catalysts (Scheme ). However, no main group- or transition metal-based catalyst has been reported to date for experimentally realizing such an approach to exploit the excellent hydrogen storage compound NH 3 BH 3 in reducing CO 2 under ambient conditions, although stoichiometric methods mediated by an equivalent amount of external Lewis base or frustrated Lewis pair (FLP) were achieved employing 1 or 10 atm of CO 2 pressure at 50–80 °C (Scheme ). On the contrary, transition metal-catalyzed nonsolvolytic and solvolytic hydrogen generation from NH 3 BH 3 has been a topic of extensive study, but there have been several practical problems related to the (economical) regeneration of NH 3 BH 3 from its byproducts and also the purity of the produced H 2 gas .…”