CO Insertion Reaction Research Articles

Polar molecules catalyze CO insertion into metal-alkyl bonds through the displacement of an agostic C-H bond

The insertion of CO into metal-alkyl bonds is the key C-C bond-forming step in many of the most important organic reactions catalyzed by transition metal complexes. Polar organic molecules (e.g., tetrahydrofuran) have long been known to promote CO insertion reactions, but the mechanism of their action has been the subject of unresolved speculation for over five decades. Comprehensive computational studies [density functional theory (DFT)] on the prototypical system Mn(CO)5(arylmethyl) reveal that the polar molecules do not promote the actual alkyl migration step. Instead, CO insertion (i.e. alkyl migration) occurs rapidly and reversibly to give an acyl complex with a sigma-bound (agostic) C-H bond that is not easily displaced by typical ligands (e.g. phosphines or CO). The agostic C-H bond is displaced much more readily, however, by the polar promoter molecules, even though such species bind only weakly to the metal center and are themselves then easily displaced; the facile kinetics of this process are attributable to a hydrogen bonding-like interaction between the agostic C-H bond and the polar promoter. The role of the promoter is to thereby catalyze isomerization of the agostic product of CO insertion to give an [Formula: see text]-C,O-bound acyl product that is more easily trapped than the agostic species. This ability of such promoters to displace a strongly sigma-bound C-H bond and to subsequently undergo facile displacement themselves is without reported precedent, and could have implications for catalytic reactions beyond carbonylation.

Carbon monoxide insertion at a heavy p-block element: unprecedented formation of a cationic bismuth carbamoyl.

Major advances in the chemistry of 5th and 6th row heavy p-block element compounds have recently uncovered intriguing reactivity patterns towards small molecules such as H2, CO2, and ethylene. However, well-defined, homogeneous insertion reactions with carbon monoxide, one of the benchmark substrates in this field, have not been reported to date. We demonstrate here, that a cationic bismuth amide undergoes facile insertion of CO into the Bi-N bond under mild conditions. This approach grants direct access to the first cationic bismuth carbamoyl species. Its characterization by NMR, IR, and UV/vis spectroscopy, elemental analysis, single-crystal X-ray analysis, cyclic voltammetry, and DFT calculations revealed intriguing properties, such as a reversible electron transfer at the bismuth center and an absorption feature at 353 nm ascribed to a transition involving σ- and π-type orbitals of the bismuth-carbamoyl functionality. A combined experimental and theoretical approach provided insight into the mechanism of CO insertion. The substrate scope could be extended to isonitriles.

Strain‐Induced Double Carbon–Carbon Bond Activations of Cycloparaphenylenes by a Platinum Complex: Application to the Synthesis of Cyclic Diketones

AbstractThe carbon–carbon (C−C) bond activation of [n]cycloparaphenylenes ([n]CPPs) by a transition‐metal complex is herein reported. The Pt0 complex Pt(PPh3)4 regioselectively cleaves two C−C σ bonds of [5] CPP and [6]CPP to give cyclic dinuclear platinum complexes in high yields. Theoretical calculations reveal that the relief of ring strain drives the reaction. The cyclic complex was further transformed into a cyclic diketone by using a CO insertion reaction.

Strain-Induced Double Carbon-Carbon Bond Activations of Cycloparaphenylenes by a Platinum Complex: Application to the Synthesis of Cyclic Diketones.

The carbon-carbon (C-C) bond activation of [n]cycloparaphenylenes ([n]CPPs) by a transition-metal complex is herein reported. The Pt0 complex Pt(PPh3 )4 regioselectively cleaves two C-C σ bonds of [5] CPP and [6]CPP to give cyclic dinuclear platinum complexes in high yields. Theoretical calculations reveal that the relief of ring strain drives the reaction. The cyclic complex was further transformed into a cyclic diketone by using a CO insertion reaction.

Rhodium-Catalyzed Hydrocarboxylation: Mechanistic Analysis Reveals Unusual Transition State for Carbon–Carbon Bond Formation

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 co-workers 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. First, 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. Second, the substrates show an unusual coordination mode during CO2 insertion, with the nucleophilic carbon positioned up to 3.6 A away from rhodium. In order to understand the experimentally observed substrate preferences, we have analyzed a set ...

Acceleration of CO2 insertion into metal hydrides: ligand, Lewis acid, and solvent effects on reaction kinetics.

The insertion of CO2 into metal hydrides and the microscopic reverse decarboxylation of metal formates are important elementary steps in catalytic cycles for both CO2 hydrogenation to formic acid and methanol as well as formic acid and methanol dehydrogenation. Here, we use rapid mixing stopped-flow techniques to study the kinetics and mechanism of CO2 insertion into transition metal hydrides. The investigation finds that the most effective method to accelerate the rate of CO2 insertion into a metal hydride can be dependent on the nature of the rate-determining transition state (TS). We demonstrate that for an innersphere CO2 insertion reaction, which is proposed to have a direct interaction between CO2 and the metal in the rate-determining TS, the rate of insertion increases as the ancillary ligand becomes more electron rich or less sterically bulky. There is, however, no rate enhancement from Lewis acids (LA). In comparison, we establish that for an outersphere CO2 insertion, proposed to proceed with no interaction between CO2 and the metal in the rate-determining TS, there is a dramatic LA effect. Furthermore, for both inner- and outersphere reactions, we show that there is a small solvent effect on the rate of CO2 insertion. Solvents that have higher acceptor numbers generally lead to faster CO2 insertion. Our results provide an experimental method to determine the pathway for CO2 insertion and offer guidance for rate enhancement in CO2 reduction catalysis.

Carbon Dioxide Insertion into Group 9 and 10 Metal-Element σ Bonds.

Carbon dioxide (CO2) is an appealing feedstock for the sustainable preparation of a variety of carbon-based commodity chemicals because of its high abundance, low cost, and nontoxicity. The high kinetic and thermodynamic stability of CO2, however, means that there are currently only a limited number of practical catalytic systems for the conversion of CO2 into more valuable chemicals, and continued research in this area is required. One promising approach for the eventual transformation of CO2 is to initially insert the molecule into transition-metal-element σ bonds such as M-H, M-OR, M-NR2, and M-CR3 bonds to form products of the type M-OC(O)E (E = H, OR, NR2, or CR3). CO2 insertion has been demonstrated in numerous stoichiometric reactions involving transition-metal complexes, but in cases where insertion results in the formation of strong M-O bonds, the products are often too stable to undergo further transformations. Group 9 and 10 transition-metal complexes (M = Ni, Pd, Pt, Co, Rh, or Ir) form relatively weak M-O bonds, and as a consequence, a number of group 9 and 10 transition-metal catalysts in which CO2 insertion is proposed as an elementary step in catalysis have been developed. In this Award Article, we summarize group 9 and 10 transition-metal complexes in which CO2 insertion into a metal-element σ bond to form a M-OC(O)E-type product has been observed. Mechanistic similarities and differences are highlighted by comparing CO2 insertion reactions in different types of group 9 and 10 metal-element σ bonds, and a general trend for predicting the rate-determining step of the insertion process is described based on the nucleophilicity of the element in the σ bond. Although we focus on stoichiometric reactivity, the relevance of CO2 insertion to catalytic reactions is also emphasized throughout the paper.

E[sbnd]H (E = N, O) bond activation by a nucleophilic palladium carbene

EH bond cleavage by [{PC(sp2)P}Pd(PMe3)] (1, PC(sp2)P = iPr2PC6H4CC6H4PiPr2) of alcohols led to a series of new square-planar tridentate palladium alkoxides, [{PC(sp3)HP}Pd(OiPr)] (3), [{PC(sp3)HP}Pd(OtBu)] (4), and [{PC(sp3)HP}Pd(OPh)] (5, PC(sp3)HP = bis[2-(di-iso-propylphosphino)phenyl]methyl). The analogous reaction with amines led to the formation of [{PC(sp3)HP}Pd(NPh2)] (6) and [{PC(sp3)HP}Pd(NHMes)] (7). The molecular structure of 7 was further probed by a CO2 insertion reaction into the PdN bond, yielding the corresponding carbamate 8. The molecular structures of 3–8 were determined by single-crystal X-ray diffraction and conform to the corresponding solution structures as determined by NMR spectroscopy. The reactivity of carbene 1 towards alcohols and amines is dictated by the nucleophilic/basic character at the carbene backbone carbon atom, the pKa and bond dissociation energy of the EH bond (E = N, O), and the steric properties of the organic substrates used.

Copper-Catalyzed Stereodefined Construction of Acrylic Acid Derivatives from Terminal Alkynes via CO2 Insertion.

IPrCuCl catalyzes the CO2 insertion reaction undergone by a dialkylvinylborane intermediate derived from alkynyltrialkylborate by a 1,2-alkyl group migration to afford α-alkyl acrylic acids with excellent regio- and stereoselectivities.

Theoretical prediction on CO insertion reactions through the anionic complex [ClMg(η2-O2C]− as a catalyst

The mechanisms of the reaction of CO inserting into the CH bond of furane/thiofuran through the anionic magnesium–CO2 complex [ClMg(η2-O2C)]− as a reaction catalyst are investigated using the second-order Møller-Plesset (MP2), and the polarized continuum model (PCM) is applied to simulate the solvent effects. Calculated results show that the insertion reaction route includes three steps: (i) the dehydrogenation of furane/thiofuran through the capturing of the anion complex [ClMg(η2-O2C)]− with strong carbene character, results in an intermediate I, (ii) the addition of CO via the CC bond formation between the carbon atom of I and the carbon atom of CO through the partial negative charge transfer into the π∗ orbital of CO, forms an anion species III, and (iii) H abstraction from the neutral complex [ClMg(η2-O2CH)]0 produces the aldehyde product. We find that the reactions of CO inserting into the CH bond of furane/thiofuran is an endothermic process, and the H abstraction to form aldehyde species (corresponding transition states TS3) is the rate-determining step. Meanwhile, solvent effect is important for the CO insertion reaction, for example, the barrier of TS3 in THF solvent is lower by 5kcal/mol than corresponding that in acetone solvent. We expected that the understanding of the insertion reaction can provide valuable insights into related reactions.

ChemInform Abstract: Synthesis of (+)‐trans‐Dihydrolycoricidine by an Organocatalytic Enantioselective Friedel—Crafts Reaction

Abstractas a key step

New insights into the effects of Mn and Li on the mechanistic pathway for CO hydrogenation on Rh-Mn-Li/SiO2 catalysts

It has been reported widely that Rh-Mn-Li/SiO2 catalysts can exhibit high selectivity to C2+ oxygenates during CO hydrogenation, with promoters of Mn and Li playing an important role in this behavior. In this study, a series catalysts of Rh-Mn-Li/SiO2 with different amounts of Mn and Li were prepared, and the new insights into the effects of Mn and Li on the mechanistic pathway for C2+ oxygenates synthesis from syngas were investigated. The XPS analysis showed that Rh existed mainly as metallic Rh after reduction, however partially positively charged Rhδ+ atoms appeared on the surface of Mn-containing catalyst due to the interaction of Rh-Mn. The results of H2-TPR indicated that both of Li and Mn can inhibit the reduction of Rh2O3. With the increase in the ratio of Mn/Rh, the most effective interaction, associated to the presence of two reduction centers of Rh2O3, was obtained when the ratio of Mn/Rh=1. In situ-FTIR was used to probe the effects of Mn and Li on CO absorption and hydrogenation. With regards to the CO adsorption, the doping of Mn can enhance the CO adsorption ability of Rh and weaken the CO-Rh bond strength very effectively when the amount of Mn reached 1.5wt.%. Improved capacity of CO adsorption is conducive to increase of CO conversion, while the weakening of CO-Rh bond is beneficial to the CO insertion reaction, thus contributing to the generation of C2+ oxygenates. Moreover, the low amount of Li (≤0.075wt.%) can also enhance the CO adsorption, resulting in the improvement of reactivity. On the other hand, Mn and Li promoted dissociation of H2, which is favorable to an increase in the rate of hydrogenation. But an opposite effect appeared at high content of Mn (>1.5wt.%). As the optimized results, when Rh, Mn, Li content was 1.5wt.%, 1.5wt.% and 0.075wt.%, the catalyst for CO hydrogenation of C2+ oxygenates achieved the best performance of C2+ oxygenates synthesis.

A kinetic model for the synthesis of ethanol from syngas and methanol over an alkali-Co doped molybdenum sulfide catalyst: Model building and validation at bench scale

A set of experiments was run in laboratory and bench scale reactors over an alkali-Co doped molybdenum sulfide catalyst in order to develop and validate the kinetics of higher alcohol synthesis from syngas/methanol mixtures. The purpose is to generate a kinetic model useful to design a mixed alcohol process where methanol is recycled to the reactor to increase ethanol production. Experimental data from a laboratory scale reactor were fitted using a power-law model, considering a CO insertion reaction scheme. The model was validated with a group of experiments carried out at a bench scale reactor, consisting of experiments with methanol co-feeding and gas recycle. Finally, we also studied whether a model would be able to predict the effect of methanol co-feeding if its parameters were determined by fitting only the experiments where methanol co-feeding was not performed.

Synthesis of (+)‐trans‐Dihydrolycoricidine by an Organocatalytic Enantioselective Friedel–Crafts Reaction

AbstractThe amaryllidaceae alkaloid (+)‐trans‐dihydrolycoricidine (1) was synthesized by asymmetric organocatalytic Friedel–Crafts reaction of sesamol with nitro‐olefin followed by an intramolecular Henry reaction for construction of the C ring system. Construction of the B ring was achieved by a microwave‐assisted palladium‐catalyzed CO insertion reaction. Finally, regio‐ and stereoselective introduction of the third hydroxyl group (at C3) on the C ring afforded 1.

Formation of Acyl and Dioxycarbene Ruthenium Complexes via Double C–S Bond Cleavage and CO Insertion

Abstract Ruthenium complexes containing an N,N,C,S-metalloligand or an N,N,C,O-organoligand with a sulfido carbonyl Ru cluster were obtained by the reaction of 6-(4′′-dibenzothienyl)-2,2′-bipyridine with [Ru3(CO)12]. The dibenzothienyl group undergoes double carbon–sulfur bond cleavage and CO insertion reactions to give a bridging acyl group and a metallacyclic dioxycarbene donor.

Metal- and ligand-assisted CO2 insertion into Ru-C, Ru-N, and Ru-O bonds of ruthenium(II) phosphine complexes: a density functional theory study.

The CO2 insertion reactions of [L4Ru(η(2)-CH2C6H4)] (1), [L4Ru(η(2)-OC6H3Me)] (2), and [L4Ru(η(2)-NHC6H4)] (3), where L = PH3 and PMe3, are modeled using density functional theory methods. In 1 and 2, the metal-assisted CO2 insertion occurs because of the favorable initial axial phosphine dissociation mechanism, whereas in 3, the ligand (NHC6H4)-assisted mechanism operates (ΔG(⧧) = +19.0 kcal/mol), wherein the nucleophilic affinity of the -NHC6H4 moiety aids the CO2 insertion process. The modeled mechanisms are consistent with the experimental findings by Hartwig et al. (J. Am. Chem. Soc, 1991, 113, 6499), in which the rate of the reactions of 1 and 2 depends on the added phosphine concentration, whereas the rate of the reaction of 3 is independent of the added phosphine concentration. In 1 and 2, CO2 is preferably inserted into the Ru-Caryl bond rather than the competitive Ru-CH2 and Ru-O bonds, respectively. In 1, the π-type orbital interaction of the aryl ring with the metal center is found to stabilize the transition state for Ru-Caryl bond insertion (ΔG(⧧) = +25.7 kcal/mol). In 2, the Ru-Caryl insertion (ΔG(⧧) = +23.0 kcal/mol) is thermodynamically preferred, while the kinetically preferred Ru-O bond insertion (ΔG(⧧) = +17.4 kcal/mol) is highly reversible. The more electron-donating and sterically bulky PMe3 facilitates the CO2 insertion of 1 and 2 because the initial dissociation of axial PMe3 is easier than that of PH3 by ca. +11.0 kcal/mol, whereas in the case of 3, the effect of PMe3 slightly increases the ΔG(⧧) value of 3. The increase in the nucleophilic affinity of amido nitrogen in 3 and the increase in the polarity of the solvent decrease the ΔG(⧧) value of 3 by 48%. The inclusion of the chelating dimethylphosphinoethane ligand in 3 along with the electron-donating substituent at the -NHC6H4 moiety and the polar solvent further reduces the ΔG(⧧) value of 3 by 62%, which demonstrates the role of the chelating ligand, electron-donating substituent, and polar solvent in the ligand-assisted CO2 insertion reactions.

Supported imidazole as heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO2

Imidazole anchored onto a silica matrix, by means of a propyl linkage, is found to be an effective heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO2 in near quantitative yield. The versatility of this catalyst is demonstrated by using different substrates (epichlorohydrin, propylene oxide, butylene oxide and styrene oxide) for this cycloaddition reaction. These CO2 insertion reactions were typically carried out in the temperature range of 343 to 403K at 0.6MPa CO2 pressure under solvent-free conditions. Several spectroscopic methods were used to characterize the catalyst and study the integrity of the fresh and spent catalysts.

Kinetic Aspects for the Reduction of CO2and CS2with Mixed-Ligand Ruthenium(II) Hydride Complexes Containing Phosphine and Bipyridine

A new water-soluble ruthenium hydride complex [Ru(H)(bpy)2(PTA)]PF6 (bpy = 2,2'-bipyridine, PTA = 1,3,5-triaza-7-phosphaadamantane) (1a) was prepared. 1a reacted with CO2 and CS2 to give the corresponding formate and dithioformate complexes, respectively. Both the insertions of CO2 and CS2 into the Ru-H bond of 1a followed second-order kinetics. The second-order rate constant (k2) of CO2 insertion reaction varied from (9.40 ± 0.41) × 10(-4) M(-1) s(-1) in acetone to (1.13 ± 0.08) × 10(-1) M(-1) s(-1) in methanol; moreover, the ln(k2) is in good linear relationship with the acceptor number (AN) of the solvent used. Although, the k2 of CS2 insertion reaction ranged from (3.43 ± 0.10) M(-1) s(-1) in methanol to (24.0 ± 0.5) M(-1) s(-1) in N,N-dimethylformamide, which is 1000 times faster than CO2 insertion. Generally, the k2 of CS2 insertion increased with the static dielectric constant (D(s)) of the reaction medium investigated. For comparison purposes, we further investigated the reactivity of [Ru(H)(bpy)2(PPh3)]PF6 (PPh3 = triphenylphosphine) (1b) with CO2 and CS2. 1b reacted with CO2 slowly in the methanol with a k2 of (1.46 ± 0.09) × 10(-3) M(-1) s(-1), yielding a formate complex [Ru(η(1)-OC(H)═O)(bpy)2(PPh3)]PF6 (2b). The reaction of 1b with CS2 is 1000 times faster than that of CO2. The structures of 1a, 1b, and 2b were determined by X-ray crystallographic analysis.

Effect of environment around the active center Cu+ species on the catalytic activity of CuY zeolites in dimethyl carbonate synthesis: A theoretical study

A density functional theory method has been used to investigate the effect of environment around the active center Cu+ species on the catalytic activity in the oxidative carbonylation of methanol to dimethyl carbonate over CuY zeolites. Based on the configuration of Cu+ located in the supercage, Cu+ or Cs+ species at the sites adjacent to the active center Cu+ species in the supercage are considered as the surrounding environment. The results indicate that the presence of Cu+ in the supercage adjacent to the active center improves the adsorption energy of co-adsorbed CO and elongates the CuOCH3 bond in co-adsorbed CO/CH3O system, stabilizes the transition state for the reaction of CO insertion, and ultimately makes the active center Cu+ species exhibit better catalytic activity. Whereas, Cu+ species at adjacent site in the smallcage plays an opposite role. More importantly, introducing Cs species into the supercage of CuY zeolite significantly improves the adsorption energy of co-adsorbed CO and the stability of transition state configuration for CO insertion reaction, thus, leads to the best catalytic performance among four types of catalysts, which is consistent with the previous experimental results.

On carbon dioxide capture: An accurate ab initio study of the Li3N + CO2 insertion reaction

The picture of an insertion reaction with formation of a fully lithiated carbamate is presented inspired in recent experimental information and based on accurate electronic structure calculations. A study is performed of the Li3N+CO2 reaction, which was recently suggested as a candidate to capture carbon dioxide and yield useful chemicals. Investigated in the gas phase, the results predict Li3N to leave its planar equilibrium form when capturing CO2 that bends itself during the capture process. A species with the sum formula Li3NCO2 is formed which, jointly with its fragments, is characterized in detail by Møller–Plesset perturbation theory and the coupled cluster method. The practical interest of the title reaction and work ahead are also assessed.