1,721,181 research outputs found
Amination of C-H Bonds by Metal Porphyrins Catalysed Nitrene Transfer Reaction
No full textThe biological and pharmaceutical activities of organonitrogen compounds prompted the scientific community to develop new methods for the direct and selective C-N bond formation, working within restricted financial parameters and environmentally friendly requirements.In the last few years we have reported on the catalytic activity of metal porphyrin complexes in a wide range of reactions, such as olefin epoxidation,1 hydrocarbon amination and olefin aziridination. For these last reactions arylazides, a versatile class of starting material, was employed as atom-efficient aminating agents.2 ArN3 generate a nitrene functionality “ArN” and the eco-friendly molecular nitrogen is the only side product.
The selective insertion of “ArN” into C–H bonds of benzylic substrates or olefins yields benzylic amines, benzylic imines or allylic amines. To clarify the mechanism of the C-H amination reactions, the ruthenium bis-imido porphyrin complex (1) was isolated and characterised by X-ray analysis.
The role of 1 in catalytic nitrene insertions into C H bonds was studied in the reaction of ArN3 with several hydrocarbons proving that 1 is an active reaction intermediate. It also appears to have equilibrium between stability and reactivity.3 To the best of our knowledge, complex 1 is the first structurally characterized bis-imido porphyrin complex that shows a good catalytic activity in this class of reactions.
References: [1] S. Fantauzzi, E. Gallo, E. Rose, N. Raoul, A. Caselli, S. Issa, F. Ragaini, S. Cenini, Organometallics , 2008, 27, 6143; [2] For a review see: S. Fantauzzi, A. Caselli and E. Gallo, Dalton Trans., 2009, 5434; [3] S. Fantauzzi, E. Gallo, A. Caselli, F. Ragaini, N. Casati, P. Macchi and S. Cenini Chem. Commun., 2009, 3952–395
Mechanistic study of the Ru-3(CO)(12)/chloride catalyzed carbonylation reactions of nitroarenes to carbamates and ureas; the role of the alkylammonium cation
No full textThe effect of the chloride countercation on the mechanism of the Ru-3(CO)(12)/chloride catalyzed carbonylation of nitroarenes to carbamates has been investigated. The reason for the higher activity and selectivity obtained with tetraethylammonium chloride with respect to [PPN][Cl] is due to the higher igroscopicity of the former (only when no aniline is added) and to its ability do decompose to yield triethylamine. The role of this last compound is twofold. On one hand, it accelerates the alcoholysis of the intermediately formed diarylurea. On the other, it favors a reaction pathway that consumes aniline together with nitrobenzene, thus converting a by-product into the desired product. (C) 2000 Elsevier Science B.V. All rights reserved
Mechanistic studies of palladium-catalysed carbonylation reactions of nitro compounds to isocyanates, carbamates and ureas
No full textMany different palladium-based catalytic systems have been reported for the carbonylation reactions of organic nitro compounds to isocyanates, carbamates and ureas. Almost all of these can be roughly divided into three groups: (i) those containing a second (or even a third) metal (usually a Lewis acid or a metal oxo compound or both), (ii) those in which phenanthroline or similar chelating nitrogen ligands are used and (iii) those in which monodentate phosphines are employed as ligands. The systems in which chelating phosphines are used as ligands lie in between the last two groups. The reaction mechanisms for the catalytic systems in each group appear to be related. Most of the information available does not derive from strictly mechanistic studies, but rather from synthetic studies and it is here critically analysed and compared with the information obtained from other related fields
Intermediate formation of anilines in the synthesis of Schiff bases from nitroarenes and aldehydes
No full textThe role of the intermediate formation of anilines in the synthesis of Schiff bases from nitroarenes, aldehydes and CO catalysed by metal complexes has been investigated. Contrary to earlier belief, the reaction does not proceed through the reaction of an intermediate nitrene with the carbonyl compound, but by reduction of the nitroarene by CO and traces of water to initially afford the aniline, which then reacts with the aldehyde to afford the Schiff base, regenerating the water necessary to reduce more nitroarene. (C) 1999 Elsevier Science B.V. All rights reserved
MECHANISTIC STUDY OF THE CARBONYLATION OF NITROBENZENE CATALYZED BY THE [RH(CO)4]- NITROGEN BASE SYSTEM - X-RAY STRUCTURE OF [PPN][RH(CO)2ON(C6H3CL2)C(O)O]
No full text[PPN] [Rh(CO)4] (1) reacts with ArNO2 or ArNO to yield the same product (Ar = Ph, 2; Ar = 3,4-Cl2-C6H3, 3). The reaction of 1 with nitrosoarenes also produces the corresponding azoxyarenes. The product was structurally characterized in the case of Ar = 3,4-dichlorophenyl and was shown to be [PPN][Rh(CO)2ON(C6H3Cl2)C(O)O] (3). Crystal data for 3: C45H33Cl2N2O5P2Rh.C4H8O, M(r) = 989.64, triclinic, space group P1BAR (No. 2), a = 10.798(4) angstrom, b = 9.889(6) angstrom, c = 21.648(6) angstrom, a = 89.77(1)degrees, beta = 96.00(1)degrees, gamma = 92.71(1)degrees, V = 2296(2) angstrom2, Z = 2, D()c = 1.431 g cm-3, Mo Kalpha radiation (lambda = 0.710 73 angstrom), mu(Mo Kalpha) = 6.00 cm-1, R = 0.037 (R(w) = 0.047) for 5299 independent reflections having I > 3sigma(I). Both of the reactions proceed through electron transfer to the nitroso or nitro derivative. Reaction of 2 and 3 with MeOH and CO produced the corresponding amine or the methyl carbamate, depending on the experimental conditions. The reaction of 3 with MeOH/CO was faster in the presence of nitrogen bases, and aniline was shown to be an intermediate in the synthesis of the carbamate. When the same reaction was performed in the presence of a large excess of nitrosobenzene, the two isomeric mixed azoxybenzenes 3,4-Cl2-C6H3N(O)=NPh and 3,4-Cl2-C6H3N=N(O)Ph were the largely dominant products, which strongly suggests the intermediate formation of a nitrene complex
Low oxidation states ruthenium chemistry. V. The oxidation of cyclohexene catalyzed by tris(triphenylphosphine)ruthenium dichloride and related complexes
No full textPhosphorus Acids as Highly Efficient Promoters for the Palladium-Phenanthroline Catalyzed Carbonylation of Nitrobenzene to Methyl Phenylcarbamate
No full textA new family of promoters, based on phosphorus acids, is reported for the catalytic carbonylation of nitrobenzene to methyl phenylcarbamate by palladium-phenanthroline complexes. With the new promoters, unprecedented reaction rates (TOF up to 6000/h) and catalyst stability (TON up to 105) could be reached. The best promoter is phosphoric acid, which is also very cheap, nontoxic and easily separable from the reaction products
Reactions of amines with Pt(PPh3)2O2
No full textBy reaction of Pt(PPh3)2O2 with {A figure is presented} ethanol the complexes Pt(PPh3)2 {A figure is presented} (R = R′ = H; R = H, R′ = NO2; RR′ = {A figure is presented} obtained. The analogous derivatives isolated from Pt(PPh3)2O2 and the ortho-diamines with R = H, R′ = Me or R = R′= Me, showed some peculiar spectroscopic properties. A related reaction has been carried out with {A figure is presented} being isolated; the latter was also obtained from cis-Pt(PPh3)2Cl2 and {A figure is presented} in a basic medium. The platinum diamido complexes can be reversibly protonated with HBF4 to give [Pt(PPh3)2 {A figure is presented} (BF-4)2 H2O Attempted reactions of Pt(PPh3)2O2 with NH3, NH2CH2CH2NH2 an p-RC6H4NH2 (R = Me, OMe, NO2) did not give well characterizable products, while with But-NH2 an already known cluster complex was obtained
Use of amido Grignard reagents in inorganic chemistry : Synthesis and crystal structure of anti-[Pd(Cl)(py)(mu-2,6-Pri2C6H3NH)](2)
Full text linkTreating a pyridine (py) solution of PdCl2(py)(2) with a tetrahydrofuran or diethyl ether solution of the amido Grignard reagent 2,6-(Pr2C6H3NH)-C-1(MgCl) afforded a dimeric palladium complex, containing two bridging amido groups, which has been structurally characterised
Arylazo and aryldiimine derivatives of ruthenium
No full textThe reaction of (Ph3P)2Ru(CO)3 with (p-RC6H4N2)+(BF4-) (R = NO2, F, OMe, H) or (p-Me2NC6H4N2)+(BPh4-) gave arylazo complexes, [p-RC6H4N2Ru(CO)2(PPh3)2]+X-, which were protonated with HBF4 to give diimines [p-RC6H4N:NHRu(CO)2(PPh3)2]2+ (BF4-)2
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