N‐Aryl and N‐Alkyl Carbamates from 1 Atmosphere of CO₂

Abstract

We have successfully isolated and characterized the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) (1; phen=1,10‐phenanthroline), formed as an intermediate during the Zn(OAc)2/phen‐catalyzed synthesis of organic carbamates from CO2, amines, and the reusable reactant Si(OMe)4. Density functional theory calculations revealed that the direct reaction of 1 with Si(OMe)4 proceeds via a five‐coordinate silicon intermediate, forming organic carbamates. Based on these results, the catalytic system was improved by using Si(OMe)4 as the reaction solvent and additives like KOMe and KF, which promote the formation of the five‐coordinated silicon species. This sustainable and effective method can be used to synthesize various N‐aryl and N‐alkyl carbamates, including industrially important polyurethane raw materials, starting from CO2 under atmospheric pressure.

Direct Conversion of Low-Concentration CO2 into N-Aryl and N-Alkyl Carbamic Acid Esters Using Tetramethyl Orthosilicate with Amidines as a CO2 Capture Agent and a Catalyst

“…When Si­(OMe) 4 was used as an alkoxide source and dehydrating agent for the synthesis of CAEs in our previous study, some catalysts were required for efficient reactivity. , We also reported a reaction in which low-concentration CO 2 was captured by amines and DBU as carbamic acid salts that were subsequently reacted with Ti­(OR′) 4 to obtain CAEs . Therefore, considering that DBU would function as a catalyst and CO 2 adsorbent, we reacted low-concentration CO 2 with DBU and Si­(OMe) 4 without an additional catalyst.…”

“…In addition, we have established a method for regenerating Si­(OR′) 4 from (R′O) 3 SiOSi­(OR′) 3 , which is the product of the reaction between Si­(OR′) 4 and H 2 O, using the corresponding alcohols . Furthermore, in the presence of Si­(OR′) 4 , a Zn­(II) complex catalyst, and a metal salt additive (KOMe or KF) under 1 atm of CO 2 N -aryl CAEs were obtained in high yields (81–98% for 12 examples) even at temperatures and reaction times lower than those reported in our previous studies (Scheme b) . However, pure CO 2 , a metal-complex catalyst, and an additive are essential to obtain high yields of CAEs in the above system.…”

Synthesis of organic carbamates as polyurethane raw materials from CO2: the quest for metal alkoxides as regenerable reagents

“…We performed reaction mechanism analysis by experimental methods for the Zn(OAc) 2 /phen-catalyzed organic carbamate synthesis from CO 2 . 48 First, Zn(OAc) 2 , phen, and PhNH 2 were heated in MeCN under the assumption that the zinc catalyst activates the amine rather than CO 2 and Si(OMe) 4 ; however, the expected zinc amide complex 8 was not obtained (Scheme 10a). On the other hand, a similar reaction under CO 2 pressure yielded zinc carbamate complex 9 corresponding to the compound with CO 2 inserted into the Zn–N bond in 8 (Scheme 10b).…”

“…In this paper, we review several examples of our previously reported regenerable reagents, namely tin alkoxides, 42 titanium alkoxides, 43,44 and alkoxysilanes (Scheme 3d). [45][46][47][48]…”

Copper-Catalyzed Oxidative Coupling of Quinazoline-3-Oxides: Synthesis of O-Quinazolinic Carbamates

“…In recent years, organic carbamates have attracted much attention from the synthetic community due to their diverse interesting properties. − In addition to being an important class of privileged structures in pharmaceuticals in the forms of drugs and prodrugs, the carbamate motif is also broadly existed in agrochemicals and polymers. − The most common methods to organic carbamates rely on the nucleophilic addition of alcohols to isocyanates or isocyanate intermediates generated in situ form acyl azides via Curtius rearrangement (Scheme ). − In addition, the utilization of CO 2 , ,,− CO, ,− or COCl 2 − as C1 synthon to combine with amines and alcohols provides an alternative convenient access to organic carbamates. − Very recently, some supplementary strategies have also been developed through transition metal-catalyzed or novel rearrangement process. − …”