Computational and Experimental Insights into Asymmetric Rh‐Catalyzed Hydrocarboxylation with CO 2 (original) (raw)
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Organometallics, 2018
The mechanism of rhodium-COD-catalyzed hydrocarboxylation of styrene-derivatives and α,β-unsaturated carbonyl compounds with CO2 has been investigated using density functional theory (PBE-D2/IEFPCM). The calculations support a catalytic cycle as originally proposed by Mikami and coworkers including β-hydride elimination, insertion of the unsaturated substrate into a rhodium-hydride bond and subsequent carboxylation with CO2. The CO2 insertion step is found to be rate-limiting. The calculations reveal two interesting aspects: Firstly, during C-CO2 bond formation, the CO2 molecule interacts with neither the rhodium complex nor the organozinc additive. This appears to be in contrast to other CO2 insertion reactions, where CO2-metal interactions have been predicted. Secondly, the substrates show an unusual coordination mode during CO2 insertion, with the nucleophilic carbon positioned up to 3.6 Å away from rhodium. In order to understand the experimentally observed substrate preferences, we have analyzed a set of five alkenes: an α,β-unsaturated ester, an α,β-unsaturated amide, styrene and two styrene-derivatives. The computational results and additional experiments reported here indicate that the lack of activity with amides is caused by a too high barrier for CO2 insertion and is not due to catalyst inactivation. Our experimental studies also reveal two putative side reactions, involving oxidative cleavage or dimerization of the alkene substrate. In the presence of CO2, these alternative reaction pathways are suppressed. The overall insights may be relevant for the design of future hydrocarboxylation catalysts.
Metal-Catalyzed Carboxylation of Organic (Pseudo)halides with CO2
ACS Catalysis, 2016
The recent years have witnessed the development of metal-catalyzed reductive carboxylation of organic (pseudo)halides with CO 2 as C1 source, representing potential powerful alternatives to existing methodologies for preparing carboxylic acids, privileged motifs in a myriad of pharmaceuticals and molecules displaying significant biological properties. While originally visualized as exotic cross-coupling reactions, a close look into the literature data indicates that these processes have become a fertile ground, allowing for the utilization of a variety of coupling partners, even with particularly challenging substrate combinations. As for other related cross-electrophile scenarios, the vast majority of reductive carboxylation of organic (pseudo)halides are characterized by their simplicity, mild conditions, and a broad functional group compatibility, suggesting that these processes could be implemented in late-stage diversification. This perspective describes the evolution of metal-catalyzed reductive carboxylation of organic (pseudo)halides from its inception in the pioneering stoichiometric work of Osakada to the present. Specific emphasis is devoted to the reactivity of these coupling processes, with substrates ranging from aryl-, vinyl-, benzyl-to unactivated alkyl (pseudo)halides. Despite the impressive advances realized, a comprehensive study detailing the mechanistic intricacies of these processes is still lacking. Some recent empirical evidence reveal an intriguing dichotomy exerted by the substitution pattern on the ligands utilized; still, however, some elementary steps within the catalytic cycle of these reactions remain speculative, in many instances invoking a canonical cross-coupling process. Although tentative, we anticipate that these processes might fall into more than one distinct mechanistic category depending on the substrate utilized, suggesting that investigations aimed at unraveling the mechanistic underpinnings of these processes will likely bring new and innovative research grounds in this vibrant area of expertise.
Mechanistic Insights into Copper-Catalyzed Carboxylations
Organometallics, 2020
The copper-NHC-catalyzed carboxylation of organoboranes with CO2 was investigated using computational and experimental methods. The DFT and DLPNO-CCSD(T) results indicate that nonbenzylic substrates are converted via an inner sphere carboxylation of an organocopper intermediate, whereas benzylic substrates may simultaneously proceed along both inner and outer sphere CO2 insertion pathways. Interestingly, the computations predict that two conceptually different carboxylation mechanisms are possible for benzylic organoboranes, one being coppercatalyzed and one being mediated by the reaction additive CsF. Our experimental evaluation of the computed reactions confirms that carboxylation of non-benzylic substrates requires coppercatalysis, whereas benzylic substrates can be carboxylated with and without copper.
Theoretical study of TBD-catalyzed carboxylation of propylene glycol with CO2
Journal of Molecular Catalysis A: Chemical, 2010
The mechanisms for the reaction of propylene glycol (PG) with CO 2 catalyzed by 1,5,7-triazabicyclo [4.4.0]dec-5-ene (TBD) were theoretically investigated by density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level. Through analyzing the optimized structures and energy profiles along the reaction paths, the PG-activated route was identified as the most probable reaction path, in which the rate-determining step was the nucleophilic attack of one of the O atoms in CO 2 on the hydroxyl linked C atom in PG with energy barrier 56.96 kcal/mol. The catalytic role of TBD could be considered as a proton bridge activated by the synergistic action of its N atoms.
ChemSusChem, 2017
Reductive carboxylation of terminal alkynes utilizing CO2 and H2 as reactants is an interesting and challenging transformation. Theoretical calculations indicated it would be kinetically possible to obtain cinnamic acid, the reductive carboxylation product, from phenylacetylene in a CO2 /H2 system with an N-heterocyclic carbene (NHC)-supported Ag/Pd bimetallic catalysts through competitive carboxylation/hydrogenation cascade reactions in one step. These calculations were verified experimentally with a poly-NHC-supported Ag/Pd catalyst. By tuning the catalyst composition and reaction temperature, phenylacetylene was selectively converted to cinnamic acid, hydrocinnamic acid, or phenylpropiolic acid in excellent yields.
Iron-Catalyzed Regioselective Remote C(sp2)-H Carboxylation of Naphthyl and Quinoline Amides
The Journal of Organic Chemistry, 2019
Iron(III)-catalyzed regioselective direct remote C-H carboxylation of naphthyl and quinoline amides has been developed using CBr 4 and alcohol. The reaction involves a radical pathway using a coordination activation strategy and single electron transfer process. The use of sustainable iron-catalysis, selectivity and the substrate scope are the important practical features. The selective carboxylation of pervasive C Ar −H bonds is one of the most important transformations for the synthesis of aryl carboxylic acid derivatives, which are classified as the versatile building blocks in the construction of biologically active molecules, pharmaceuticals and fine chemicals. 1 Thus, the gases 2 such as CO 2 , CO and their surrogates 3 are considerably studied using metal and metal-free conditions for this purpose. With the emergence of the directed C-H functionalization, 4 efforts are recently made to develop the site-selective C-H carboxylation of arenes. In this realm, Yu and co-workers reported a Pd-catalyzed ortho-selective carboxylation of aryl carboxylic acids and anilides using CO as the C1 source (See SI, Scheme S1a). 5 Soon after, Iwasawa and coworkers demonstrated a Rh-catalyzed ortho-selective carboxylation of 2-phenylpyridines employing CO 2 as the C1 source (Scheme S1a). 6 Later, Greaney and co-workers demonstrated a Ru-catalyzed meta-selective carboxylation of 2-phenylpyridines using CBr 4 as the C1 source