Catalytic reductive carbonylation of aromatic nitro compounds to urethanes promoted by supported palladium activated with 1,10-phenanthroline derivatives

A simple catalytic system, involving supported Pd and a phenanthroline in equimolar ratio, has been shown to be very active and selective in reductive carbonylation of nitroaromatic compounds to the corresponding urethanes when the reaction is conducted in anhydrous ethanol and in the presence of a catalytic amount of a weak non-esterifiable, Brönsted acid. The chelating nitrogen donor ligand plays the role taken in other systems by large amounts of Lewis acids involving activation of the supported metals, probably to favour a fragmentation process which gives active homogeneous species. The system works best at 170–190°C and CO pressures as low as 40 bars, with turnover numbers of up to 125 cycles per hour.     

Reaction mechanism of the reductive elimination in the catalytic carbonylation of methanol. A density functional study

Reductive elimination, the final step of the Monsanto and Cativa processes, has been studied using the density functional theory with the hybrid B3LYP exchange and correlation functional. To our knowledge, this is the first systematic computational study of the reductive elimination for which even the experimental studies are rare. We have studied different isomers of the anionic dicarbonyls [Rh(CO)₂(COCH₃)I₃]⁻ (1) and [Ir(CO)₂(COCH₃)I₃]⁻ (2). Several possible reaction routes for the elimination of CH₃COI from 1 and 2 have been explored. In addition, different isomers of the neutral tricarbonyl [Ir(CO)₃(COCH₃)I₂] (3) and possible reaction paths connected to 3 have been studied. Our results show mer,trans-1 to be the dominant intermediate in the rhodium system although its transformation to fac,cis-1 and the elimination from this seems to be the most likely reaction pathway. In the anionic iridium system, the dominating intermediate is proposed to be fac,cis-2. In the neutral iridium system, mer,cis-3 is proposed to be the dominant intermediate. While inspecting the iridium system as a whole, one could propose a transformation from anionic dicarbonyl to neutral tricarbonyl that would enhance the total rate of the reductive elimination. This observation is similar to that already verified in the 1,1-insertion in the Cativa process. In general, the geometrical arrangement of the different ligands has a large effect on the catalytic activity of the different possible intermediates of these processes.     

Theoretical study on the mechanism of iron carbonyls mediated isomerization of allylic alcohols to saturated carbonyls

The conversion of allylic alcohols to enols mediated by Fe(CO)(3) has been studied through density functional theoretical calculations. From the results obtained a complete catalytic cycle has been proposed in which the first intermediate is the [(allyl alcohol)Fe(CO)(3)] complex. This intermediate evolves to the [(enol)Fe(CO)(3)] complex through two consecutive 1,3-hydrogen shifts involving a pi-allyl hydride intermediate. The highest Gibbs energy transition state corresponds to the partial decoordination ot the enol ligand prior to the coordination of a new allyl alcohol molecule that regenerates the first intermediate. Alternative processes for the [(enol)Fe(CO)(3)] complex such as [Fe(CO)(3)]-mediated enol-aldehyde transformation and enol isomerization have also been considered. The results obtained show that the former process is unfavourable, whereas the enol isomerization may compete with the enol decoordination step of the catalytic cycle.     

High-pressure synthesis of carbamates by the carbonylation of aromatic nitro compounds in cyclohexanol

A study was carried out on the high-pressure carbonylation of nitrobenzene and 3-chloronitrobenzene by CO in cyclohexanol in the presence of PdCl₂-FeCl₃-pyridine with the formation of cyclohexyl-N-phenylcarbamate and cyclohexyl-N-3-chlorophenylcarbamate in 90–95% yield and nitro compound conversion of 95–99%. The feasibility of the repeated use of this catalyst was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1885–1887, August, 1991.     

A polarographic study of aliphatic nitro compounds

Conclusions Study of the electrochemical reduction of tert-nitrobutane and 2,2-dinitropropane has shown that passage from the mononitroalkanes to the gem-dinitroalkanes involves an alteration in the reduction mechanism.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1719–1724, August, 1976.     

Radiolytic reactions of nitro blue tetrazolium under oxidative and reductive conditions: a pulse radiolysis study

The radiolytic reactions of the ditetrazolium salt nitro blue tetrazolium chloride (NBTCl₂) were studied by pulse radiolysis technique in aqueous solution under reducing and oxidising conditions with the aim of potential dosimetry application. Under reducing conditions the fast formation of the tetrazolinyl radical is observed that is followed by the appearance of monoformazan (MF⁺), i.e. one of the tetrazolium rings is reduced to formazan. The formation of the water-insoluble diformazan, i.e. the result of the second reduction step was not observed in pulse radiolysis. Formazan formation was not found under oxidative conditions.     

The formation of iron carbonyl radical anions in the reactions of iron carbonyls with trimethylamine N-oxide

The interaction of iron carbonyls, Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂ with Me₃NO occurs according to a one-electron redox-disproportionation scheme giving rise to iron carbonyl radical anions: Fe₂(CO)₈^·− (1), Fe₃(CO)₁₂^·− (2), Fe₃(CO)₁₁^·− (3) and Fe₄(CO)₁₃^·− (4). The role of Me₃NO, inducing CO-substitution, consists of the generation of reactive 17-electron species with a labile coordination sphere in which the substitution for other ligands occurs, resulting from fast ligand and electron exchange in the confines of the ETC-reaction.     

A theoretical study of steric and electronic effects in the rhodium-catalyzed carbonylation reactions.

We present a QM and QM/MM study of steric and electronic effects in the main steps of Rh-catalyzed carbonylation reactions. All the considered systems adopt a square-planar geometry prior to CH(3)I oxidative addition. As regards the octahedral complexes after CH(3)I oxidative addition, a comparison between the various models indicates that the energy gain due to the CH(3)I oxidative addition is reduced by the steric pressure of the substituents on the ligand. The substantially similar results obtained with the QM/MM and QM models indicate that electronic effects are not particularly relevant in determining the energetic of oxidative addition. As regards the P,P-Ph octahedral complex, the geometries in which the CO group is trans to the added CH(3) group, or trans to one of the P atoms, are of similar energy. A comparison between the various models indicates that the energy barrier of the CO insertion reaction is lowered by the presence of substituents on the chelating ligands. This effect is related to a relief of the steric pressure on the complex as the systems move from a six-coordinated octahedral geometry toward a five-coordinated square-pyramidal geometry. The energy barrier calculated for the P,S-Ph system is in rather good agreement with the experimental value, whereas that of the P,P-Ph system is somewhat underestimated. Inclusion of solvent effects with a continuum model leads to a slightly better agreement. The thermodynamic products adopt a square-pyramidal geometry with the COCH(3) group in the apical position.     

金催化剂上脂肪族硝基化合物与醛在氢气中选择还原耦合

采用TiO2上高度分散的金纳米粒子做催化剂,从脂肪族硝基化合物、醛和氢气可高选择性合成硝酮。与碳负载Pt催化剂相比,该催化体系上硝酮的选择性从50%增加到90%。其催化性能可有活性位结构、载体特性和反应条件精确调节。