Influence of various P/N and P/P ligands on the palladium-catalysed reductive carbonylation of nitrobenzene

Phenyl Formate as a CO Surrogate for the Reductive Cyclization of Organic Nitro Compounds to Yield Different N-Heterocycles: No Need for Autoclaves and Pressurized Carbon Monoxide

The reductive cyclization of different organic nitro compounds by carbon monoxide, catalyzed by transition metal complexes, is a very efficient and clean strategy for the synthesis of many N-heterocycles. However, its use requires the use of autoclaves and pressurized CO lines. In this perspective, the authors will present the results obtained in their laboratories on the use of phenyl formate as a convenient CO surrogate, able to liberate carbon monoxide under the reaction conditions and allowing the use of a cheap glass pressure tube as a reaction vessel. In most cases, yields were better than those previously reported by the use of pressurized CO, proving that the use of CO surrogates can be a viable alternative to the gaseous reagent.

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.

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.

Efficient alkene hydrosilation with bis(8-quinolyl)phosphine (NPN) nickel catalysts. The dominant role of silyl-over hydrido-nickel catalytic intermediates

A cationic nickel complex of the bis(8-quinolyl)(3,5-di-tert-butylphenoxy)phosphine (NPN) ligand, [(NPN)NiCl]+, is a precursor to efficient catalysts for the hydrosilation of alkenes with a variety of hydrosilanes under mild conditions and low catalyst loadings. DFT studies reveal the presence of two coupled catalytic cycles based on [(NPN)NiH]+ and [(NPN)NiSiR3]+ active species, with the latter being more efficient for producing the product. The preferred silyl-based catalysis is not due to a more facile insertion of alkene into the Ni-Si (vs. Ni-H) bond, but by consistent and efficient conversions of the hydride to the silyl complex.

Featuring Xantphos

This review highlights the use of the bisphosphine ligand group in homogeneous catalysis.

Crystal structures of di-chlorido-palladium(II), -platinum(II) and -rhodium(III) complexes containing 8-(di-phenyl-phosphan-yl)quinoline

The crystal structures of di-chlorido-palladium(II), -platinum(II) and -rhodium(III) complexes containing 8-(di-phenyl-phosphan-yl)quinoline, (SP-4)-[PdCl2(C21H16NP)], (1) [systematic name: di-chlor-ido-(8-di-phenyl-phosphanyl-quinoline)-palladium(II)], (SP-4)-[PtCl2(C21H16NP)]·CH2Cl2, (2) [systematic name: di-chlorido-(8-di-phenyl-phos-phanyl-quinoline)-platinum(II) dichlorometh-ane monosolvate], and (OC-6-32)-[RhCl2(C21H16NP)2]PF6·0.5CH2Cl2·0.5CH3OH, (3) [systematic name: cis-di-chlor-ido-bis-(8-di-phenyl-phosphanyl-quinoline)-rhodium(III) hexa-fluorido-phos-phate di-chloro-methane/-methanol hemisolvate] are reported. In these complexes, the phosphanyl-quinoline acts as a bidentate ligand, forming a planar asymmetrical five-membered chelate ring. The palladium(II) and platinum(II) complex mol-ecules in (1) and (2), respectively, show a typical square-planar coordination geometry and form a dimeric structure through an inter-molecular π-π stacking inter-action between the quinolyl rings. The centroid-centroid distances between the stacked six-membered rings in (1) and (2) are 3.633 (2) and 3.644 (2) Å, respectively. The cationic rhodium(III) complex in (3) has a cis(Cl),cis(P),cis(N) (OC-6-32) configuration of the ligands, in which two kinds of intra-molecular π-π stacking inter-actions are observed: between the quinolyl and phenyl rings and between two phenyl rings, the centroid-centroid distances being 3.458 (2) and 3.717 (2) Å, respectively. The PF6 (-) anion in (3) is rotationally disordered, the site occupancies of each F atom being 0.613 (14) and 0.387 (14). The CH2Cl2 and CH3OH solvent mol-ecules are also disordered and equal site occupancies of 0.5 are assumed.

The addition of bromine and iodine to palladacyclopentadienyl complexes bearing bidentate heteroditopic P−N spectator ligands derived from differently substituted quinolinic frames. The unexpected evolution of the reaction

The palladacyclopentadienyl complexes with substituted phosphoquinolines react with halogens giving σ-butadienyl or a zwitterionic derivative depending on the ligand structure.

Síntese e emprego do [Pd(dmba)(NCO)(PPh3)] em processos catalíticos envolvendo a preparação de derivados da uréia e de alcoxicarbonil complexos

Este trabalho trata do emprego do ciclometalado [Pd(dmba) (NCO)(PPh3)] (dmba = N,N-dimetilbenzilamina; PPh3 = trifenilfosfina) em processos catalíticos em fase homogênea, envolvendo a reação entre p-toluidina e p-nitrotolueno, produzindo N,N'-bis(4-metilfenil)uréia. A reação foi realizada a 140 0C, sob pressão inicial de CO de 60 bar. Empregou-se também o mesmo composto em reações de carbonilação na presença dos álcoois metílico e etílico, obtendo-se os alcoxicarbonil complexos [Pd(NCO)(CO2R)(PPh3)2] (R=Me ou Et). Constatou-se que o emprego do [Pd(dmba)(NCO)(PPh3)] nos referidos processos, propiciou a formação dos produtos com bons rendimentos.