Carbon Dioxide Insertion Research Articles

Reversible CO2 insertion into the silicon-nitrogen σ-bond of an N-heterocyclic iminosilane.

The reversible insertion of carbon dioxide into the silicon-nitrogen bond of an N-heterocyclic iminosilane is reported. Solution-phase thermodynamic investigations indicate that this process is thermoneutral and reversible, whereas in the solid-phase CO2 can be stored for extended periods and is only released upon heating to 133 °C.

Carbon Dioxide Insertion into Rhenium Hydrides as a Probe for the Impact of Solvent on Linear Free Energy Relationships between Thermodynamic and Kinetic Hydricity

Carbon Dioxide Insertion into Rhenium Hydrides as a Probe for the Impact of Solvent on Linear Free Energy Relationships between Thermodynamic and Kinetic Hydricity

Highly Regio- and Stereoselective C-C Bond Transformations via Insertion of Carbon Dioxide Promoted by Ni-Catalytic Systems

Highly Regio- and Stereoselective C-C Bond Transformations via Insertion of Carbon Dioxide Promoted by Ni-Catalytic Systems

Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel-Boron Cooperativity in a PBP-Ni Complex.

The synthesis and characterization of (tBu PBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni-C bond of (tBu PBP)NiMe (1) is presented. An unexpected CO2 cleavage process involving the formation of new B-O and Ni-CO bonds leads to the generation of a butterfly-structured tetra-nickel cluster (tBu PBOP)2 Ni4 (μ-CO)2 (6). Mechanistic investigation of this reaction indicates a reductive scission of CO2 by O-atom transfer to the boron atom via a cooperative nickel-boron mechanism. The CO2 activation reaction produces a three-coordinate (tBu P2 BO)Ni-acyl intermediate (A) that leads to a (tBu P2 BO)-NiI complex (B) via a likely radical pathway. The NiI species is trapped by treatment with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to give (tBu P2 BO)NiII (η2 -TEMPO) (7). Additionally, 13 C and 1 H NMR spectroscopy analysis using 13 C-enriched CO2 provides information about the species involved in the CO2 activation process.

Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel‐Boron Cooperativity in a PBP‐Ni Complex

AbstractThe synthesis and characterization of (tBuPBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1) is presented. An unexpected CO2 cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2 (6). Mechanistic investigation of this reaction indicates a reductive scission of CO2 by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2 activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A) that leads to a (tBuP2BO)−NiI complex (B) via a likely radical pathway. The NiI species is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7). Additionally, 13C and 1H NMR spectroscopy analysis using 13C‐enriched CO2 provides information about the species involved in the CO2 activation process.

Inverting the Electronic Structure of Diylidylgermylenes by Backbone Modification.

Owing to the strong electron-donating ability of ylide substituents, diylidyltetrylenes are usually highly nucleophilic species with strong donor capacities. Here, we demonstrate that their electronic properties are in fact highly flexible and can be effectively tuned through variation of the substituent in the ylide backbone. Initial density functional theory studies showed that cyano groups are particularly capable in lowering the LUMO energy of diylidyl germylenes thus turning these usually highly nucleophilic species into electrophilic compounds. This was confirmed by experimental studies. Attempts to synthesize the germylene (YCN)2Ge [with YCN = Ph3P-(C)-CN] from the corresponding metalated ylides YCNK selectively led to germanide [(YCN)3Ge)K]2 thus reflecting the electrophilic nature of the intermediate formed germylene. XRD analysis of single crystals of (YCN)2Ge - serendipitously obtained through protonative cleavage of one ylide from the germanide - revealed a monomeric structure with rather long Ge-ylide linkages, which corroborates well with a pure single bond and no stabilization of the empty pπ orbital at germanium through pi bonding. The germanide exhibits methanide-like reactivity towards chalcogens but a likewise weak Ge-C bond as demonstrated by the insertion of carbon dioxide.

Catalytic Carboxylation of Terminal Alkynes with Copper(I) Azothioformamide Complexes

Redox-active azothioformamide (ATF) ligands produce coordination complexes with Cu(I) salts. A series of monosubstituted ligands were used to synthesize Cu(I) complexes and investigated for the catalytic insertion of carbon dioxide into terminal alkynes. The optimal catalytic conditions were found using phenylacetylene with 4 mol % of a halogen-bridged (μ-I)-para-substituted [(p-MeOATF-Cu(I)I)]2 dimer with 3 equiv of Cs2CO3 as the base in dimethyl sulfoxide under 1 atm of CO2 at 40 °C for 24 h, followed by treatment with HCl. A variety of aryl and alkyl substrates were evaluated giving yields from 47 to 99%. The reaction was computationally deconstructed, and a series of likely intermediates and associated energies are provided along with a proposed mechanism. Additionally, it was found that the conditions were suitable for one-pot esterification.

CO2 Fixation by Dimeric Tb(III) Complexes: Synthesis, Structure, and Magnetism

Two dinuclear complexes, [Tb2(L1)2(piv)2(NO3)2]·H2O (1) and [Tb2(L2)2(CF3CO2)2(H2O)4].2NO3 (2), have been prepared and characterized by single-crystal X-ray diffraction, where each metal ion is doubly phenoxido-bridged by the two phenolato oxygen atoms of the tetradentate Schiff-base ligand. Previous magnetic studies of 1 show that it is not a single-molecule magnet (SMM), while AC magnetic measurements of 2 show that it relaxes quite fast with μSQUID measurements revealing the presence of an interaction operating between the Tb ions. Through DC, μSQUID, and CASSCF calculations, the strength of the interaction in 2 can be quantified, which is of dipolar origin. Both complexes showed efficient catalytic activity toward the carbon dioxide insertion reaction into epoxides for the formation of organic cyclic carbonates. Catalytic synthesis of organic cyclic carbonates smoothly occurred at 60 °C under1 bar carbon dioxide pressure and neat conditions. Exocyclic as well as endocyclic epoxides produced a respective cyclic carbonate product with moderate to high yield (43–100%). Moreover, a high turnover number (7300–10000) along with a high turnover frequency (537.5–5000 h–1) are found in this catalytic reaction.

CO2‐Assisted Stereocontrolled Multi‐Component Coupling Reactions Promoted by Ni‐Catalytic System

AbstractA combination of Ni‐catalyst and PPh3 promotes the three‐component coupling reaction of vinyl epoxide, alkyne, and dimethylzinc under a carbon dioxide atmosphere to provide 2,5‐heptadienyl alcohols with excellent E‐stereoselectivity. The stereochemistry of the products from the multi‐component coupling reaction is controlled via an oxanickelacycle intermediate, which is formed by the insertion of carbon dioxide.

Gold-Aluminyl and Gold-Diarylboryl Complexes: Bonding and Reactivity with Carbon Dioxide.

The unconventional carbon dioxide insertion reaction of a gold-aluminyl [tBu3PAuAl(NON)] complex has been recently shown to be related to the electron-sharing character of the Au–Al bond that acts as a nucleophile and stabilizes the insertion product through a radical-like behavior. Since a gold-diarylboryl [IPrAuB(o-tol)2] complex with similar reactivity features has been recently reported, in this work we computationally investigate the reaction of carbon dioxide with [LAuX] (L = phosphine, N-heterocyclic carbene (NHC); X = Al(NON), B(o-tol)2) complexes to get insights into the Al/B anionic and gold ancillary ligand effects on the Au–Al/B bond nature, electronic structure, and reactivity of these compounds. We demonstrate that the Au–Al and Au–B bonds possess a similar electron-sharing nature, with diarylboryl complexes displaying a slightly more polarized bond as Au(δ+)–B(δ–). This feature reduces the radical-like reactivity toward CO2, and the Al/B anionic ligand effect is found to favor aluminyls over boryls, despite the greater oxophilicity of B. Remarkably, the ancillary ligand of gold has a negligible electronic trans effect on the Au–X bond and only a minor impact on the formation of the insertion product, which is slightly more stable with carbene ligands. Surprisingly, we find that the modification of the steric hindrance at the carbene site may exert a sizable control over the reaction, with more sterically hindered ligands thermodynamically disfavoring the formation of the CO2 insertion product.

Photocatalytic C–H Carboxylation of 1,3-Dicarbonyl Compounds with Carbon Dioxide Promoted by Nickel(II)-Sensitized α-Fe2O3 Nanoparticles

Insertion of carbon dioxide into C–H bonds under mild conditions is an industrially important yet highly challenging task. In the present study, we report the synthesis of an efficient photocatalyst consisting of a Ni(bpy)3Cl2 sensitizer supported on α-Fe2O3 nanoparticles for the CO2 insertion into C–H bonds, particularly carboxylation of 1,3-dicarbonyl compounds like acetyl acetone, methyl acetoacetate, and ethyl acetoacetate with CO2 under visible light irradiation using carbon tetrachloride as a solvent. The carboxylation of these compounds afforded the predominant formation of a single isomeric acid as confirmed by 13C NMR spectroscopy. Based on the computational studies, a possible reaction mechanism suggested the generation of CO2 radical anions at the conduction band of α-Fe2O3 through single electron transfer mediated by the nickel(II) complex that coupled with acetyl acetone cation radicals at the valence band of α-Fe2O3 to give the corresponding carboxylic acid. The protocol described in the present study presents a light-assisted approach and a low-cost material for the synthesis of carboxylic acids utilizing CO2 under mild reaction conditions.

Disilanes with Pentacoordinate Si Atoms by Carbon Dioxide Insertion into Aminodisilanes: Syntheses, Molecular Structures, and Dynamic Behavior.

The insertion of carbon dioxide into the Si–N bonds of aminodisilanes ((RR′N)nMe3–nSi)2 affords carbamoyloxydisilanes ((RR′NC(O)O)nMe3–nSi)2. Some of the obtained insertion products feature pentacoordinate silicon atoms in the solid state and in solution, with two carbamoyloxy moieties bridging the Si–Si bond. The aminodisilanes and their insertion products were extensively analyzed, including single-crystal X-ray structure analyses. The temperature dependence of the higher coordination was investigated using variable temperature NMR experiments.

What Singles out Aluminyl Anions? A Comparative Computational Study of the Carbon Dioxide Insertion Reaction in Gold-Aluminyl, -Gallyl, and -Indyl Complexes.

Anionic aluminum(I) anions (“aluminyls”) are the most recent discovery along Group 13 anions, and the understanding of the unconventional reactivity they are able to induce at a coordinated metal site is at an early stage. A striking example is the efficient insertion of carbon dioxide into the Au–Al bond of a gold–aluminyl complex. The reaction occurs via a cooperative mechanism, with the gold–aluminum bond being the actual nucleophile and the Al site also behaving as an electrophile. In the complex, the Au–Al bond has been shown to be mainly of an electron-sharing nature, with the two metal fragments displaying a diradical-like reactivity with CO2. In this work, the analogous reactivity with isostructural Au–X complexes (X = Al, Ga, and In) is computationally explored. We demonstrate that a kinetically and thermodynamically favorable reactivity with CO2 may only be expected for the gold–aluminyl complex. The Au–Al bond nature, which features the most (nonpolar) electron-sharing character among the Group 13 anions analyzed here, is responsible for its highest efficiency. The radical-like reactivity appears to be a key ingredient to stabilize the CO2 insertion product. This investigation elucidates the special role of Al in these hetero-binuclear compounds, providing new insights into the peculiar electronic structure of aluminyls, which may help for the rational control of their unprecedented reactivity toward carbon dioxide.

Ligand and solvent effects on CO2 insertion into group 10 metal alkyl bonds.

The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type (RPBP)M(CH3) (RPBP = B(NCH2PR2)2C6H4−; R = Cy or tBu; M = Ni or Pd) to generate κ1-acetate complexes of the form (RPBP)M{OC(O)CH3} is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual RPBP ligand, which features a central boryl donor that exerts a strong trans-influence, and the identification of a new decomposition pathway that results in C–B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into (RPBP)M(CH3) is facile and occurs at room temperature because of the high trans-influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using (tBuPBP)Pd(CH3). These studies demonstrate that the Dimroth–Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into (tBuPBP)M(CH3) (M = Ni or Pd) proceeds via an SE2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization.

Titanium isopropoxide-mediated cis-selective synthesis of 3,4-substituted butyrolactones from CO2.

We report a Ti(OiPr)4-mediated multicomponent reaction, which produces 3,4-substituted cis-δ-lactones from alkyl magnesium chloride, benzaldehyde and CO2. The key intermediate, titanacyclopropane, is formed in situ from Ti(OiPr)4 and a Grignard reagent, which enables 1,2-dinucleophilic reactivity that is used to insert carbon dioxide and an aldehyde. An alternative reaction route is also described where a primary alkene is used to create the titanacyclopropane. A computational analysis of the elementary steps shows that the carbon dioxide and the aldehyde insertion proceeds through an inner-sphere mechanism. A variety of cis-butyrolactones can be synthesized with up to 7 : 1 diastereoselectivity and 77% yield.

Aluminium‐based ruthenium/diamine catalysts for produce aliphatic polycarbonates from carbon dioxide and oxetanes

AbstractWe fabricated the chiral ArDPEN/Ru species within the nanoparticles of the aluminium (Al/ArDPEN/Ru). Electron microscopy photos and the anatomical properties revealed the uniformly dispersed nanoparticles with active single‐site ruthenium/diamine centres on the exterior nanoparticles shell. Al/ArDPEN/Ru showed catalytic properties for the reaction of CO2 with oxetane, to synthesize the corresponding polycarbonate with minimal amount of ether linkages. TMC is prepared by a backbiting method following ring‐opening of oxetane by the anion initiator, subsequent to carbon dioxide insertion into the ruthenium/diamine bond. The preparation of the copolymer is shown to proceed mostly by method of the anionic ring‐opening polymerization of preformed trimethylene carbonate in the presence of an anion in solution. In addition, the catalyst anatomical heterogeneity of Al/ArDPEN/Ru was characterized by various techniques, including XRD, SEM, TGA, TEM, VSM, and FT‐IR. No leaching of ruthenium into the solution was observed.

Reactivity of aluminum hydrides supported with sterically hindered acenaphthene-1,2-diimines towards CO2

• Bulky aluminum hydrides. • Acenaphthene-1,2-diimine ligands. Insertion of carbon dioxide. The reactions of [(Ar BIG -bian)Al(H) 2 Li(THF) 4 ] ( 1 ) (Ar BIG -bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene, THF = tetrahydrofuran), [(dpp-bian)Al(H) 2 Li(THF) 3 ] ( 2 ) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) and [(dpp-bian)AlH(Cl)][Na(DME) 3 ] ( 3 ) (DME = 1,2-dimethoxyethane) with carbon dioxide proceed with its insertion into Al–H bonds and afford [(Ar BIG -bian)Al{μ-OC(H)O} 2 Li(THF) 2 ] ( 4 ), [{(dpp-bian)AlOC(H)OLi(THF) 3 } 2 μ-O] ( 5 ) and [(dpp-bian)Al(µ-O){µ-OC(H)O}Al(dpp-bian)][Na(DME) 3 ] ( 6 ) respectively. Complex 5 is a product of thermally induced transformation of bis-formate intermediate [(dpp-bian)Al{μ-OC(H)O} 2 Li(THF) n ] ( 5a ), which can be isolated from the reaction of 2 and CO 2 at ambient temperature. Newly prepared compounds were characterized by IR and NMR spectroscopy; molecular structures of products 4, 5 and 6 were established by single-crystal X-ray analysis.

Coinage metal aluminyl complexes: probing regiochemistry and mechanism in the insertion and reduction of carbon dioxide.

The synthesis of coinage metal aluminyl complexes, featuring M–Al covalent bonds, is reported via a salt metathesis approach employing an anionic Al(i) (‘aluminyl’) nucleophile and group 11 electrophiles. This approach allows access to both bimetallic (1 : 1) systems of the type (tBu3P)MAl(NON) (M = Cu, Ag, Au; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) and a 2 : 1 di(aluminyl)cuprate system, K[Cu{Al(NON)}2]. The bimetallic complexes readily insert heteroallenes (CO2, carbodiimides) into the unsupported M–Al bonds to give systems containing a M(CE2)Al bridging unit (E = O, NR), with the μ-κ1(C):κ2(E,E′) mode of heteroallene binding being demonstrated crystallographically for carbodiimide insertion in the cases of all three metals, Cu, Ag and Au. The regiochemistry of these processes, leading to the formation of M–C bonds, is rationalized computationally, and is consistent with addition of CO2 across the M–Al covalent bond with the group 11 metal acting as the nucleophilic partner and Al as the electrophile. While the products of carbodiimide insertion are stable to further reaction, their CO2 analogues have the potential to react further, depending on the identity of the group 11 metal. (tBu3P)Au(CO)2Al(NON) is inert to further reaction, but its silver counterpart reacts slowly with CO2 to give the corresponding carbonate complex (and CO), and the copper system proceeds rapidly to the carbonate even at low temperatures. Experimental and quantum chemical investigations of the mechanism of the CO2 to CO/carbonate transformation are consistent with rate-determining extrusion of CO from the initially-formed M(CO)2Al fragment to give a bimetallic oxide that rapidly assimilates a second molecule of CO2. The calculated energetic barriers for the most feasible CO extrusion step (ΔG‡ = 26.6, 33.1, 44.5 kcal mol−1 for M = Cu, Ag and Au, respectively) are consistent not only with the observed experimental labilities of the respective M(CO)2Al motifs, but also with the opposing trends in M–C (increasing) and M–O bond strengths (decreasing) on transitioning from Cu to Au.

Partnering a Three-Coordinate Gallium Cation with a Hydroborate Counter-Ion for the Catalytic Hydrosilylation of CO2.

A novel β-diketiminate stabilized gallium hydride, (Dipp L)Ga(Ad)H (where (Dipp L)={HC(MeCDippN)2 }, Dipp=2,6-diisopropylphenyl and Ad=1-adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga-H bond under mild conditions. In this case, treatment of the resulting κ1 -formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C6 F5 )3 , (Dipp L)Ga(Ad)H catalyses the reductive hydrosilylation of CO2 . Under stoichiometric conditions, the addition of one equivalent of B(C6 F5 )3 to (Dipp L)Ga(Ad)H leads to the formation of a 3-coordinate cationic gallane complex, partnered with a hydroborate anion, [(Dipp L)Ga(Ad)][HB(C6 F5 )3 ]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO2 to the formaldehyde oxidation level at 60 °C in the presence of Et3 SiH (yielding H2 C(OSiEt3 )2 ). When catalysis is undertaken in the presence of excess B(C6 F5 )3 , appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H2 C(OSiEt3 )2 , CH4 and O(SiEt3 )2 . While this system represents proof-of-concept in CO2 hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h-1 ). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (Dipp L)Ga(Ad){OC(H)OB(C6 F5 )3 }, and the correspondingly slow rate of the turnover-limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(Dipp L)Ga(Ad)]+ cation (AN=69.8).

Multivalent Bifunctional Carbosilane Dendrimer-Supported Ammonium and Phosphonium Organocatalysts for the Coupling of CO2 and Epoxides

Insertion of carbon dioxide into the structure of organic epoxides leads to the formation of valuable cyclic carbonates and polycarbonates. For the purpose of this process, we report here a series of recyclable organocatalysts with superior activity. Carbosilane dendrimers (first to third generation) are employed as a support to which periphery ammonium or phosphonium centers are covalently attached to form a dendritic ionic liquid (DIL). The obtained DILs were tested as homogeneous catalysts in the cycloaddition of CO₂ to epoxides with respect to their activity and recyclability. The catalytic performance of active sites is enhanced by the presence of a proximal hydroxyl group, playing the role of a hydrogen bond donor. An experimentally observed synergistic effect was confirmed by density functional theory calculations. The activity of DILs is affected more by the structure of onium salt than by the size of the support (dendrimer generation). The dendritic catalysts of all tested generations could be recovered by nanofiltration and repeatedly reused. In order to simplify the separation of the catalysts, composite materials were prepared by intercalating the more active ammonium dendrimers into the interlayer space of a natural montmorillonite. The resulting heterogeneous catalysts were easily separable by centrifugation while retaining a reasonable level of activity.