Mechanistic Study of the L2Pd-Catalyzed Reduction of Nitrobenzene with CO in Methanol: Comparative Study between Diphosphane and 1,10-Phenanthroline Complexes

Catalysis of Synergistic Reactions by Host-Guest Assemblies: Reductive Carbonylation of Nitrobenzenes

Numerous chemical transformations require two or more catalytically active sites that act in a concerted manner; nevertheless, designing heterogeneous catalysts with such multiple functionalities remains an overwhelming challenge. Herein, it is shown that by the integration of acidic flexible polymers and Pd-metallated covalent organic framework (COF) hosts, the merits of both catalytically active sites can be utilized to realize heterogeneous synergistic catalysis that are active in the conversion of nitrobenzenes to carbamates via reductive carbonylation. The concentrated catalytically active species in the nanospace force two catalytic components into proximity, thereby enhancing the cooperativity between the acidic species and Pd species to facilitate synergistic catalysis. The resulting host-guest assemblies constitute more efficient systems than the corresponding physical mixtures and the homogeneous counterparts. Furthermore, this system enables easy access to a family of important derivatives such as herbicides and polyurethane monomers and can be integrated with other COFs, showing promising results. This study utilizes host-guest assembly as a versatile tool for the fabrication of multifunctional catalysts with enhanced cooperativity between different catalytic species.

Molybdenum-Mediated Reductive Hydroamination of Vinylcyclopropanes with Nitroarenes: Synthesis of Homoallylamines

A molybdenum-mediated reductive hydroamination of vinylcyclopropanes with nitroarenes has been developed. A broad range of substituted homoallylamines were prepared in good to excellent yields from readily available starting materials. No noble metal catalysts were used in this reaction, and Mo(CO)₆ acted as both catalyst and reductant. This protocol provides an effective method for the selective synthesis of substituted homoallylamines from easily available nitroarenes.

Decarbonylative/decarboxylative [4 + 2] annulation of phthalic anhydrides and cyclic iodoniums towards triphenylenes

A palladium-catalyzed decarbonylative/decarboxylative [4 + 2] annulation of phthalic anhydrides with cyclic diaryliodonium salts to synthesize triphenylenes has been developed. The reaction shows broad substrate scope with a high yield of up to 99%, and it provides an efficient and fast way to access functionalized triphenylenes in only one hour.

Reductive Carbonylation of Nitroarenes Using a Heterogenized Phen-Pd Catalyst

The reductive carbonylation of nitroarenes in the presence of MeOH and CO(g) is one of the interesting alternative routes without utilizing toxic phosgene and corrosive HCl generation for the synthesis of industrially useful carbamate compounds that serve as important intermediates for polyurethane production. Since homogeneous palladium catalysts supported by phen (phen = 1,10-phenanthroline) are known to be effective for this catalysis, the heterogenized Pd catalyst was developed using the phen-containing solid support. In this study, we report the synthesis of a phen-based heterogeneous Pd catalyst, Pd@phen-POP, which involves the solvent knitting of a phen scaffold via the Lewis-acid-catalyzed Friedel-Crafts reaction using dichloromethane as a source for linker in the presence of AlCl₃ as a catalyst. The resulting solid material has been thoroughly characterized by various physical methods revealing high porosity and surface area. Similar to the homogeneous pallidum catalyst, this heterogeneous catalyst shows efficient reductive carbonylation of various nitroarenes. The catalytic reaction using nitrobenzene as a model compound presents a high turnover number (TON = 530) and a reasonable turnover frequency (TOF = 45 h^-1), with a high selectivity (92%) for the carbamate formation. According to the recycling study, the heterogeneous catalyst is recyclable and retains ∼90% of the original reactivity in each cycle.

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes: synthesis of (E,E)-dienamides

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes has been developed. The reaction of mixtrues of E/Z isomers of 1,3-dienes reacted with nitroarenes and produced (E,E)-dienamides with high stereoselectivities.

An Escape from Noble Metals for Generating Urethanes via Reductive Carbonylation of Nitroarenes over FeSe2/γ-Al2O3 †

The reaction of FeCl3, SeO2, and Pyridine (Py) in the presence of methanol (MeOH) under CO pressure generates a black precipitate, which has been confirmed as ferric di-selenide, FeSe2 through different structure characterization methods. Furthermore, impregnation of 5 wt% of FeSe2 onto γ-Al2O3 exhibits better catalytic performance than FeSe2 due to the highly dispersed and smaller particle sizes ca. 200–300 nm. The reductive carbonylation of nitrobenzene (NB) was investigated over FeSe2/γ-Al2O3 as a heterogeneous catalyst, delivering an excellent yield and high selectivity of methyl-N-phenyl carbamate (MPC). Moreover, a set of reactions was performed with variation in the reaction time, temperature, and pressure to investigate the effects of these factors. In particular, FeSe2/γ-Al2O3 is highly stable and can be recycled for up to five cycles without significant loss in catalytic performance. A mechanistic study was also conducted on this low-cost catalyst system, especially proposing a crucial role of FeSe2 (μ-CO) active species.

Intramolecular Pd-Catalyzed Reductive Amination of Enolizable sp3-C-H Bonds

A palladium-catalyzed reductive cyclization of nitroarenes has been designed to construct sp³-C-NHAr bonds from sp³-C-H bonds by using an enolizable nucleophile to intercept a nitrosoarene intermediate. Exposure of ortho-substituted nitroarenes to 5 mol % of Pd(OAc)₂ and 10 mol % of phenanthroline under 2 atm of CO constructs partially saturated 5-, 6-, or 7-membered N-heterocycles using α-pyridyl carboxylates, malonates, 1,3-dimethylbarbituric acid, 1,3-diones, or difurans as the nucleophile.

Intermolecular π-hole/n→π* interactions with carbon monoxide ligands in crystal structures

A thorough analysis of the Cambridge Structure Database reveals that intermolecular π-hole/n→π* interactions with carbon monoxide ligands are abundant in the solid state and somewhat directional, particularly with fac-like M(CO)3 fragments (P < 4.0). High level DFT calculations suggest interacting energies up to about -10 kcal mol-1 for adducts of charge neutral complexes.

Amide synthesis via nickel-catalysed reductive aminocarbonylation of aryl halides with nitroarenes

A nickel-catalysed reductive aminocarbonylation of (hetero)aryl halides employing readily available nitro(hetero)arenes as the nitrogen source has been developed.

Aminocarbonylation of aryl halides is one of the most useful methods in amide synthesis, but nitroarenes have not been used as a nitrogen source in this method even though they are more economical and accessible than anilines. Reported here is the development of nickel catalysis for the first three-component reactions of aryl halides, Co₂(CO)₈, and nitroarenes under reductive conditions to produce aryl amides. A wide range of (hetero)aryl iodides and bromides as well as nitro(hetero)arenes are suitable reaction partners, and high functional group compatibility has been achieved. The method might be used for the streamlined synthesis of aryl amides.

Nitroarenes as the Nitrogen Source in Intermolecular Palladium-Catalyzed Aryl C-H Bond Aminocarbonylation Reactions

A three-component palladium-catalyzed aminocarbonylation of aryl and heteroaryl sp² C-H bonds using nitroarenes as the nitrogen source was achieved using Mo(CO)₆ as the reductant and origin of the CO. This intermolecular C-H bond functionalization does not requires any exogenous ligand to be added, and our mechanism experiments indicate that the palladacycle catalyst serves two roles in the aminocarbonylation reaction: reduce the nitroarene to a nitrosoarene and activate the sp² C-H bond.