Presence Of Rhodium Research Articles

Isotope effects in the oxidative functionalization of methane in the presence of rhodium-containing homogeneous catalytic systems

The combined oxidation of carbon monoxide, CH4, and CD4 by molecular oxygen (16O2 and 18O2) in aqueous solutions of trifluoroacetic acid labeled with 18O in the presence of rhodium and copper compounds and potassium iodide has been studied. The distribution of 18O in isotopically substituted products suggests that oxygen entered into the methane molecule from an active oxidizing agent. This oxidizing agent was produced from molecular oxygen under the action of reagents and catalytic system components. The kinetic isotope effect observed for methane (kH/kD=3.9−4.3) suggests a nonradical character of the step at which the oxygen atom passes from an active oxidizing agent to the methane molecule or its fragments—transition-state components of the corresponding step.

Rhodium(I) catalyzed four-component reaction of Fischer alkenyl carbene complexes and 1,1-diphenylallene

Alkyl substituted chromium Fischer carbene complexes react with 1,1-diphenylallene in the presence of rhodium(I) catalysts (10 mol%) to yield highly substituted dienyl indenone derivatives. In this process a catalytic chromium(0)–rhodium(I) exchange occurs, four new C–C bonds are created, and four-components (two allenes, the carbene ligand and one CO ligand) are joined in a chemo- and regioselective manner.

Ionic Liquids as a Convenient Recyclable Medium for the Generation of Transient Carbonyl Ylides: Syntheses of Oxa and Dioxa‐Bridged Polycyclic Systems.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ionic liquids as a convenient recyclable medium for the generation of transient carbonyl ylides: syntheses of oxa and dioxa-bridged polycyclic systems

The tandem cyclization-cycloaddition reactions of α-diazo ketones in the presence of rhodium(II) acetate, rhodium(II) octanoate or copper(II) acetyl acetonate as catalyst were performed in different imidazole based ionic liquids as solvent. A successful generation of the transient five- or six-membered-ring carbonyl ylides, followed by the 1,3-dipolar cycloaddition with olefin or carbonyl functional groups in ionic liquid is described to furnish the oxa and dioxa-bridged polycyclic systems with high stereoselectivity. Significant advantages of this process are the recovery of rhodium catalyst, the re-use of ionic liquid, replacement of hazardous organic solvents and the resulting high stereoselectivity.

Reaction of 1,1,3,3-tetramethyldisiloxane with p-substituted acetophenones in the presence of platinum and rhodium complexes

Hydrosilylation of p-substituted acetophenones XC6H4COCH3 (X = H, Me, MeO, HO, F, Cl, NO2) with 1,1,3,3-tetramethyldisiloxane in the presence of rhodium and platinum complexes was studied. The Pt(II) complexes are less active but more selective catalysts of hydrosilylation of acetophenones. Six new 1-(1′-arylethoxy)-1,1,3,3-tetramethyldisiloxanes were prepared.

Asymmetric transfer of carbenes with phenyliodonium ylides.

Phenyliodonium ylides, readily available upon treatment of CH-acidic compounds such 1,3-dicarbonyl derivatives with iodobenzene diacetate, react in the presence of rhodium(II) or copper catalysts to afford products derived from carbenoid pathways. Chemo- and enantioselectivity of the reactions are identical to those of the corresponding diazocompounds, indicating metallocarbene intermediates with both precursors. An exception to this occurs in the intramolecular cyclopropanation of phenyliodonium ylides, where a competing uncatalyzed pathway intervenes at room temperature. When phenyliodonium ylides are generated in the presence of Rh(II) catalysts and olefins, they react in situ to afford cyclopropanes.

Rh2(OAc)4‐Catalyzed Regioselective Intermolecular C—H Insertion Reactions: Novel Synthesis of 2‐Pyrrol‐3′‐yloxindoles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ruthenium, osmium and rhodium complexes of polypyridyl ligands: Metal-promoted activities, stereochemical aspects and electrochemical properties

This article presents a brief overview of the reactions of2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in presence of rhodium(III), ruthenium(II) and osmium(II) under various experimental conditions. Under certain experimental conditions tptz exhibits metal-assisted hydrolysis/hydroxylation at the triazine ring. However, synthetic methods have also been developed to prepare complexes with intact tptz. Molecular structures of some of the complexes, especially stereoisomers of the hydroxylated products, are established by single crystal X-ray studies. A critical analysis of all data suggests that the electron-withdrawing effect of the metal ion (L→Mσ donation) is the predominant factor, rather than angular strain, that is responsible for metal-promoted reactivities. Electrochemical properties of all of these complexes have been investigated, Rh(III) complexes are excellent catalysts for electrocatalytic reduction of CO2, and dinuclear Ru(II) and Os(II) complexes exhibit strong electronic communication between the metal centres.

Rh2(OAc)4-Catalyzed Regioselective Intermolecular C-H Insertion Reactions: Novel Synthesis of 2-Pyrrol-3′-yloxindoles

Regioselective synthesis of 2-pyrrol-3′-yloxindoles has been achieved by the reactions of cyclic diazo carbonyl compounds 1a-e with pyrrole and substituted pyrroles (2a-d) in the presence of rhodium(II) acetate catalyst via intermolecular C-H insertion reaction.

The influence of Rh surface doping on anomalous properties of thick-film SnO 2 gas sensors

Here there are presented new results from the investigations of SnO 2 thick-film sensor. The effects of rhodium surface doping on dc and ac properties of SnO 2 gas sensors were studied. The measurements reveal anomalous behaviour of the sensors. Below characteristic temperature, the resistance of the sensors increases in presence of reducting gases. The mechanism associated with the presence of rhodium can be connected with the increase of acceptor surface states concentration and causes the inversion of near-surface layers.

AN ENZYMATIC GLUCOSE BIOSENSOR BASED ON THE CODEPOSITION OF RHODIUM, IRIDIUM, AND GLUCOSE OXIDASE ONTO A GLASSY CARBON TRANSDUCER

The performance of a first-generation glucose biosensor based on the entrapment of glucose oxidase (GOx) within a net of iridium and rhodium codeposited onto activated glassy carbon electrode, is described. The presence of rhodium in the plating solution allows the deposition of iridium and GOx under conditions at which this is not possible without rhodium. The electrocatalytic activity of the bioelectrode containing both metals towards the oxidation and reduction of hydrogen peroxide improves drastically compared to those of the bioelectrodes containing GOx and iridium or rhodium. The sensitivity for glucose obtained with Ir-Rh-GOx/GCE is almost seven times higher than that obtained for Rh-GOx/GCE and by far higher than that for Ir-GOx/GCE which under the working conditions is almost zero. The influence of the electrodeposition conditions on the response of the bioelectrode was evaluated from the amperometric signals of hydrogen peroxide and glucose. At 0.0 V the response to glucose is linear up to 1.0 × 10−2 M. At −0.050 V, no interference occurs neither for ascorbic acid nor for uric acid even at concentrations higher than the maximum physiological levels.

Synthesis of 2 H-Thiopyrans by Rhodium(II) Acetate-Catalyzed Reaction of 4-Amino-2,5-dihydro-3-thiophenecarbonitriles with a-Diazocarbonyl Compounds II [1

The reaction of 4-amino-2,5-dihydro-2- and -5-methyl-3-thiophenecarbonitriles with α-diazocarbonyl compounds in the presence of rhodium(II) acetate gave regioselectively 4-cyano-2H-thiopyrans (C2-S insertion) in moderate to good yields; 5-cyano-2H-thiopyrans (C5-S insertion) were not isolated. The starting compounds were synthesized by reaction of tetrahydro-2- and -5-methyl-4-oxo-3-thiophenecarbonitriles with morpholine, piperidine, and pyrrolidine in the presence of formic acid in ethanol.

Oxidation of 7,8‐diaminotheophylline with lead tetraacetate and reaction of the oxidation product, 6‐cyanoimino‐5‐diazo‐1,3‐dimethylpyrimidine‐2,4‐dione with alcohols or amines

AbstractOxidation of 7,8‐diaminotheophylline (1) with lead tetraacetate in refluxing toluene gave a mixture of 3‐amino‐5,7‐dimethylpyrimido[4,5‐e][1,2,4]triazine‐6,8‐dione (2) and 6‐cyanoimino‐5‐diazo‐1,3‐dimethylpyrimidine‐2,4‐dione (4). The latter was transformed to 2 by the reaction with 1‐propanethiol in quantitative yield. The reaction of 4 with methanol, ethanol and 1‐propanol in the presence of rhodium (II) acetate gave 5‐alkoxy‐6‐(2‐alkyl‐3‐isoureido)‐1,3‐dimethylpyrimidine‐2,4‐diones (7a‐c). A similar reaction of 4 with alkylamines such as n‐propylamine, n‐butylamine, isobutylamine and n‐hexylamine gave a mixture of 7‐alkyl‐8‐aminotheophyllines (8a‐d) and (5‐alkylamino‐1,3‐dimethyl‐2,4‐dioxopyrimidin‐6‐yl)cyanamides (9a‐d).

Novel chemoselective 1,3-dipolar cycloaddition of rhodium generated carbonyl ylides with arylidenetetralones

Treatment of various α-diazo ketones 1 and arylidenetetralones 2 in the presence of rhodium(II) acetate dimer leads to spiro-dioxa ring systems 3 as the only CO addition products with high regio- and chemoselectivity.

ChemInform Abstract: Synthesis of 2H-Thiopyrans by Rhodium(II) Acetate-Catalyzed Reaction of 4-Amino-2,5-dihydro-3-thiophenecarbonitriles with α-Diazocarbonyl Compounds. Part 1.

The reaction of 4-amino-2,5-dihydro-2- and -5-methyl-3-thiophenecarbonitriles with α-diazocarbonyl compounds in the presence of rhodium(II) acetate gave regioselectively 4-cyano-2H-thiopyrans (C2-S insertion) in moderate to good yields; 5-cyano-2H-thiopyrans (C5-S insertion) were not isolated. The starting compounds were synthesized by reaction of tetrahydro-2- and -5-methyl-4-oxo-3-thiophenecarbonitriles with morpholine, piperidine, and pyrrolidine in the presence of formic acid in ethanol.

Determination of selenium by catalytic cathodic stripping voltammetry

A procedure is described for the determination of selenium in natural waters using cathodic stripping voltammetry in the presence of rhodium. Advantage is taken from a catalytic effect on the electrochemical reduction of protons in the presence of a mixed complex of selenide with rhodium and chloride, containing Cl–Rh–SeH species. The catalysis causes a very large peak-current at a negative peak potential for low (picomolar) selenium concentrations, close to the hydrogen wave. In addition to the selenium concentration, the peak height depends on the concentrations of acid (H +) and chloride, and suffers from strong interference by organic surfactants. Optimised conditions include 0.3 M HCl, 75 ppb Rh(III) and a deposition potential of −0.2 V. UV-digestion was used to eliminate the interference caused by organic material and to convert Se(VI) to Se(IV). A 3 σ detection limit of 2.4 pM Se(IV) was calculated from the standard deviation of a low selenium concentration (17 pM) using a deposition time of 50 s.

Synthesis of 2H-Thiopyrans by Rhodium(II) Acetate-Catalyzed Reaction of 4-Amino-2,5-dihydro-3-thiophenecarbonitriles with α-Diazocarbonyl Compounds. Part 1

The reaction of 4-amino-2,5-dihydro-2- and -5-methyl-3-thiophenecarbonitriles with α-diazocarbonyl compounds in the presence of rhodium(II) acetate gave regioselectively 4-cyano-2H-thiopyrans (C2-S insertion) in moderate to good yields; 5-cyano-2H-thiopyrans (C5-S insertion) were not isolated. The starting compounds were synthesized by reaction of tetrahydro-2- and -5-methyl-4-oxo-3-thiophenecarbonitriles with morpholine, piperidine, and pyrrolidine in the presence of formic acid in ethanol.

Mechanistic Studies of CVD Metallization Processes: Reactions of Rhodium and Platinum β-Diketonate Complexes on Copper Surfaces

The hexafluoroacetylacetonate complexes Rh(hfac)(C2H4)2 and Pt(hfac)2 are known to serve as chemical vapor deposition precursors to Rh and Pt thin films. In the absence of a reducing carrier gas, the depositions are surface-selective and occur preferentially on copper, but under these conditions, the metallization processes are unexpectedly inefficient relative to the rapid deposition of Pd on Cu seen for the palladium analogue Pd(hfac)2. Mechanistic studies of the reactions of Rh(hfac)(C 2H4)2 and Pt(hfac)2 on copper surfaces under ultrahigh vacuum conditions have now been performed in order to elucidate the factors responsible for the differences among these surface-selective metallization processes. The studies demonstrate that adsorption of the rhodium complex Rh(hfac)(C2H4)2 on copper surfaces is accompanied by the loss of the coordinated ethylene groups, even at 100 K. At these low temperatures, the adsorbed Rh(hfac) fragments are oriented in several ways with respect to the surface. Heating the substrate above 150 K causes the hfac ligands to realign to a perpendicular orientation relative to the surface. The platinum precursor Pt(hfac) 2 adsorbs molecularly at 100 K with the molecular planes of the hfac ligands oriented parallel to the copper surface. Heating the substrate to temperatures above 150 K again results in a realignment of the hfac ligands to a perpendicular orientation. This reorientation is accompanied by a partial reduction of the Pt centers (as judged from shifts seen in X-ray photoelectron spectroscopy core level data), a result suggesting that the hfac ligands begin to dissociate from the platinum centers near 150 K. At temperatures above 220 K, the transfer of the hfac ligands from both complexes to the copper surface is complete, as signaled by the reduction of the metal centers to the zero-valent state. The copper-bound hfac ligands are further transformed upon heating, either reacting with copper surface atoms to yield Cu(hfac)2 (which desorbs at temperatures above 250 K) or decomposing (with fragments desorbing above 350 K). The presence of platinum on the copper surface promotes the former reaction as judged by the appearance of a new reaction-limited desorption process for Cu(hfac) 2. The presence of rhodium on the copper surface does not promote the formation of Cu(hfac)2, although autocatalysis is noted in the steady-state reactive scattering data. The inability of the Rh and Pt precursors to engage in a sustained transmetalation reaction with the copper surface is attributed to the slow interdiffusion of copper through the Rh/Cu and Pt/Cu alloys that are produced in the near-surface region.

The reactions of diazo compounds with lactones. Part 2.† The reaction of cyclic 2-diazo-1,3-dicarbonyl compounds with diketene: benzofuran formation

Cyclic 2-diazo-1,3-dicarbonyl compounds react with diketene in the presence of rhodium(II) salts to give benzofurans as the major isolated products. The formation of intermediate products with exocyclic double bonds which isomerise to benzofurans provides support for the proposed mechanism which involves initial formation of a dioxaspirooctenone by a formal dipolar cycloaddition reaction of a carbenoid to the exocyclic double bond of diketene followed by the loss of carbon dioxide. Acyclic 2-diazo-1,3-dicarbonyl compounds give furans in poor yield.

Rhodium-catalyzed asymmetric 1,4-addition of arylboron reagents to α,β-unsaturated esters

Reaction of arylboron reagents, arylboronic acids or arylborates, which are readily accessible by lithiation of aryl bromides followed by treatment with trimethoxyborane, with α,β-unsaturated esters in the presence of rhodium/( S)-binap catalyst proceeded with high enantioselectivity to give high yields of optically active β-aryl esters of up to 98% ee. The enantioselectivity depends on the steric bulkiness of the ester moiety.