Presence Of Rhodium Research Articles

Role of ligand disposition and oxime…oximato hydrogen bonding upon redox non-innocent character of rhodium(III) phenylazooximates

The diaryl-azo-oxime ligands HL, 1 undergoes oxidative coordination reaction with Wilkinson’s catalyst to form two isomeric complexes of type cis-[RhIIIL2Cl(PPh3)], 2a (Cl and PPh3 are cis) and trans-[RhIIIL2Cl(PPh3)], 2b where they are trans with respect to each other. Unlike the case of 2a, the complex 2b upon treatment with sodium borohydride, can be transformed to trans-[RhIII(HL●)(L–)Cl(PPh3)], 3 and the reaction appears to progress via PCET. The disposition of ligand frameworks as well as the formation of oxime…oximato hydrogen bond appears to have a significant function for phenylazooxime to exhibit redox non-innocent behaviour in presence of rhodium(III). The compounds were characterized by electrochemical analysis, different spectral methods, single crystal XRD and optoelectronic properties, particularly the nature of transitions in the chelates were scrutinized by TD-DFT.

Numerical investigation of methane-air counterflow premixed flame into a newly designed plus-shaped chamber with platinum and rhodium catalysts coated walls

ABSTRACT In the current investigation, the counterflow methane/air premixed flame is placed in a plus-shaped burner and analyzed with and without platinum and rhodium catalytic walls. The effect of having the catalysts near the flame on the flame structure and pollutant emission is studied. To solve the problem, ReactingFOAM solver of OpenFOAM platform is used. OpenFOAM is an open-source CFD software that use object-oriented C++ custom-written codes. The ReactingFOAM uses PISO and Simple coupled algorithm method to solve the governing equations. Results indicated that the emission of NO2 is influenced, considerably by the presence of platinum near the lean, stoichiometric, and rich flame. It is also found that the presence of rhodium at the vicinity of the counterflow flame leads to a decrease in the CO formation for the flame with equivalence ratio of 0.7, 1, and 1.3 by 63, 18, and about 0%, respectively.

Mechanistically Guided One Pot Synthesis of Phosphine‐Phosphite and Its Implication in Asymmetric Hydrogenation

AbstractAlthough hybrid bidentate ligands are known to yield highly enantioselective products in asymmetric hydrogenation (AH), synthesis of these ligands is an arduous process. Herein, a one pot, atom‐economic synthesis of a hybrid phosphine‐phosphite (L1) is reported. After understanding the reactivity difference between an O‐nucleophile versus C‐nucleophile, one pot synthesis of Senphos (L1) was achieved (72 %). When L1 was treated with [Rh], 31P NMR revealed bidentate coordination to Rh. Senphos, in the presence of rhodium, catalyzes the AH of Methyl‐2‐acetamido‐3‐phenylacrylate and discloses an unprecedented turn over frequency of 2289, along with excellent enantio‐selectivity (92 %). The generality is demonstrated by hydrogenating an array of alkenes. The AH operates under mild conditions of 1–2 bar H2 pressure, at room temperature. The practical relevance of L1 is demonstrated by scaling‐up the reaction to 1 g and by synthesizing DOPA, a drug widely employed for the treatment of Parkinson's disease. Computational insights indicate that the R isomer is preferred by 3.8 kcal/mol over the S isomer.

Controlling Selectivity in the Synthesis of Z‐α,β‐Unsaturated Amidines by Tuning the N‐Sulfonyl Group in a Rhodium(II) Catalyzed 1,2‐H Shift

AbstractN2‐Sulfonyl‐α‐diazo amidines can be synthesized by the reaction of electron rich alkynyl amines with electron poor sulfonyl azides through 1,3‐dipolar cycloaddition that proceeds with perfect regioselectivity. In the presence of rhodium(II) carboxylate catalysts, denitrogenation occurs to give the corresponding metallocarbene but there are then two competing processes: 1,2–H shift and O‐transfer from the sulfonyl group to the metallocarbene center. The outcome can be controlled using an electron poor nitrobenzenesulfonyl group and large carboxylate rhodium ligands to select for 1,2–H shift, forming α,β‐unsaturated amidines in high yield and with excellent Z‐selectivity.

Tandem Insertion/[3,3]-Sigmatropic Rearrangement Involving the Formation of Silyl Ketene Acetals by Insertion of Rhodium Carbenes into S–Si Bonds

Allyl 2-diazo-2-phenylacetates are shown to react with trimethylsilyl thioethers in the presence of rhodium(II) catalysts to generate α-allyl-α-thio silyl esters. The transformation involves a tandem process involving formal rhodium-catalyzed insertion of the carbene group into the S-Si bond to generate a silyl ketene acetal, followed by a spontaneous Ireland-Claisen rearrangement. The silyl ester products were isolated as the corresponding carboxylic acids after aqueous workup. Intramolecular cyclopropanation of the allyl fragment generally competes with addition of the heteroatom to the carbene center. The reaction occurs under mild conditions and in high yield, allowing for rapid entry into rearrangement tetrasubstituted products. Propargyl esters were shown to generate the corresponding α-allenyl products.

Coordination chemistry of platinum(II) and rhodium(I) complexes containing chiral monophosphacrown ether ligands

Coordination properties of recently synthesized chiral phospha-modified crown ethers were studied in the presence of platinum(II) and rhodium(I) precursors. The prepared and in situ formed complexes were characterized by 1H and 31P NMR spectroscopies. Platinum(II)-complexes were dominantly formed as transPP arrangements, even in the case of diphosphines, possessing large bite angles, enabling to act as trans-chelating ligands. Isomers of trans-complexes were identified and explained by ligand back-bone interactions, supported by DFT calculations. Basically different complexes were formed in the presence of rhodium(I) precursors, since only one of the two phosphorous donor atoms was coordinated to the metal centre. The addition of Na[BPh4] was also examined showing dramatically different effects: sodium ion coordination to the crown ether moiety can be supposed in case of platinum complexes, while the use of rhodium(I) precursors brought about the formation of ionic complexes.

Rhodium(III)-catalysed decarboxylative C-H functionalization of isoxazoles with alkenes and sulfoxonium ylides.

Decarboxylative C-H functionalization of isoxazoles with electron-deficient alkenes and sulfoxonium ylides at the C5 position was achieved in the presence of rhodium(iii) catalysts to give the corresponding alkenylation and acylmethylation products, respectively.

Bioselective synthesis of gold nanoparticles from diluted mixed Au, Ir, and Rh ion solution by Anabaena cylindrica

Over the last years, an environmentally friendly and economically efficient way of nanoparticle production has been found in the biosynthesis of metal nanoparticles by bacteria and cyanobacteria. In this study, Anabaena cylindrica, a non-toxic cyanobacterium, is deployed in a diluted ionic aqueous mixture of equal concentrations of gold, iridium, and rhodium, of 0.1 mM each, for the selective biosynthesis of metal nanoparticles (NPs). To analyze the cyanobacterial metal uptake, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometry (ICP-MS) were applied. Only gold can be found in crystalline and nanoparticle form inside the cells of A. cylindrica, and it is the only metal for which ICP-MS analyses show a rapid decrease of the concentration in the culture medium. A slight decrease of rhodium and none of iridium was observed in the evaluated timeline of 51 h. The average diameter size of the emerging gold nanoparticles increased over the first few days, but is found to be below 10 nm even after more than 2 days. A new evaluation method was used to determine the spatially resolved distribution of the nanoparticles inside the cyanobacterial cells. This new method was also used to analyze TEM images from earlier studies of A. cylindrica and Anabaena sp., both incubated with an overall concentration of 0.8 mM Au3+ to compare the metal uptake. A. cylindrica was found to be highly selective towards the formation of gold nanoparticles in the presence of rhodium and iridium.

Performance of Pt and Pt‐Rh catalyst in the hydrogen production from glycerol

AbstractThis paper shows the behaviour of Pt and Pt‐Rh catalysts supported on α‐Al2O3 and γ‐Al2O3 for hydrogen production by glycerol aqueous phase reforming. The catalysts were prepared by wet impregnation with ion exchange correcting the pH of catalysts. The catalyst Pt/α‐Al2O3 showed low activity, high selectivity, and fast deactivation. Its behaviour was completely modified by the presence of Rh, which improved the conversion and the life span. The Pt/γ‐Al2O3 catalyst showed a different behaviour, with more conversion and high life span. The presence of rhodium in this catalyst did not change significantly the catalyst behaviour like other catalysts made with α‐alumina. The yield for hydrogen production was low for all catalysts.

Synthesis of oxazolidinones: rhodium-catalyzed C-H amination of N-mesyloxycarbamates.

N-Mesyloxycarbamates undergo intramolecular C-H amination reactions to afford oxazolidinones in good to excellent yields in the presence of rhodium(ii) carboxylate catalysts. The reaction is performed under green conditions and potassium carbonate is used, forming biodegradable potassium mesylate as a reaction by-product. This method enables the production of electron-rich, electron-deficient, aromatic and heteroaromatic oxazolidinones in good to excellent yields. Conformationally restricted cyclic secondary N-mesyloxycarbamates furnish cis-oxazolidinones in high yields and selectivity; DFT calculations are provided to account for the observed selectivity. trans-Oxazolidinones were prepared from acyclic secondary N-mesyloxycarbamates using Rh2(oct)4. The selectivity was reverted with a cytoxazone N-mesyloxycarbamate precursor using large chiral rhodium(ii) carboxylate complexes, affording the corresponding cis-oxazolidinone. This orthogonal selectivity was used to achieve the formal synthesis of (-)-cytoxazone.

ChemInform Abstract: A New Rhodium/Copper‐Cocatalyzed C—H Oxidation for the Preparation of Isoquinolin‐1‐ones.

A new and efficient rhodium/copper-cocatalyzed C–H oxidation reaction of isoquinolinium N-amides has been developed. In the presence of rhodium(II) acetate dimer, copper(II) chloride, a ligand and sodium tert-butoxide, a variety of isoquinolin-1-ones were prepared in moderate to good yields via ortho C–H oxidation.

A New Rhodium/Copper-Cocatalyzed C–H Oxidation for the Preparation of Isoquinolin-1-ones

A new and efficient rhodium/copper-cocatalyzed C–H oxidation reaction of isoquinolinium N-amides has been developed. In the presence of rhodium(II) acetate dimer, copper(II) chloride, a ligand and sodium tert-butoxide, a variety of isoquinolin-1-ones were prepared in moderate to good yields via ortho C–H oxidation.

Asymmetric hydrogenation of 2,3-dihydro-1H-inden-1-one oxime and derivatives

Asymmetric hydrogenation of 2,3-dihydro-1H-inden-1-one oxime and derivatives to produce the corresponding optically active amine has been performed in the presence of rhodium and iridium catalysts. The optimization of neutral rhodium based catalytic systems by varying the operating conditions and the ligand around the metallic centre led to high conversions with moderate enantiomeric excesses.

Rhodium(i)-catalysed skeletal reorganisation of benzofused spiro[3.3]heptanes via consecutive carbon–carbon bond cleavage

Skeletal reorganisation of benzofused spiro[3.3]heptanes has been achieved using rhodium(i) catalysts. The reaction of benzofused 2-(2-pyridylmethylene)spiro[3.3]heptanes proceeds via sequential C-C bond oxidative addition and β-carbon elimination. On the other hand, benzofused spiro[3.3]heptan-2-ols undergo two consecutive β-carbon elimination processes. In both cases, substituted naphthalenes are obtained.

ChemInform Abstract: ′On‐water′ Generation of Carbonyl Ylides from Diazoamides: Rhodium(II) Catalyzed Synthesis of Spiroindolo‐Oxiranes and ‐Dioxolanes with an Interesting Diastereoselectivity.

Abstract The ‘on-water’ generation of carbonyl ylide dipoles from diazoamides in the presence of rhodium(II) acetate dimer as the catalyst was demonstrated for the first time to synthesize spiroindolo-oxiranes and -dioxolanes. Unusual generation of carbonyl ylides with aromatic aldehydes having electron-withdrawing substituents and 1,3-dipolar cycloaddition reactions with aromatic aldehydes having electron-donating substituents were described in water with complete diastereoselectivity. This discovery provides an environmentally friendly way to generate carbonyl ylide dipoles and to synthesize substituted spiro-heterocycles in water with stereoselectivity, avoiding the use of toxic halogenated organic solvents.

Azomethine Ylide: An Isolable 1,5-Dipole for Affecting [5+2] Cy­cloaddition Reactions

It was recently found that 1-sulfonyl-1,2,3-triazole can act as a 1,3-dipole in the presence of rhodium(II), leading to emergence of diverse rhodium(II)-catalyzed [3+n] cycloaddition reactions using 1-sulfonyl-1,2,3-triazole. Herein, we highlight development of another dipole, azomethine ylide, which was prepared from 1-sulfonyl-1,2,3-triazole with amide and pyridine derivatives, respectively. Notably, the rhodium(II)-catalyzed reaction of 1-sulfonyl-1,2,3-triazole with pyridines resulted in generation of uniquely isolable azomethine ylide. This azomethine ylide is the first example of an isolable 1,5-dipole that could be cyclized with 2π-dipolarophiles. The new 1,5-dipole provides an avenue for the development of new organic syntheses. 1 Introduction 2 Reactions of 1-Sulfonyl-1,2,3-triazole with Aldehyde 3 1-Sulfonyl-1,2,3-triazole as a Precursor of Azomethine Ylide 4 Generation of Free Azomethine Ylide 5 Outlook

‘On-water’ generation of carbonyl ylides from diazoamides: rhodium(II) catalyzed synthesis of spiroindolo-oxiranes and -dioxolanes with an interesting diastereoselectivity

The ‘on-water’ generation of carbonyl ylide dipoles from diazoamides in the presence of rhodium(II) acetate dimer as the catalyst was demonstrated for the first time to synthesize spiroindolo-oxiranes and -dioxolanes. Unusual generation of carbonyl ylides with aromatic aldehydes having electron-withdrawing substituents and 1,3-dipolar cycloaddition reactions with aromatic aldehydes having electron-donating substituents were described in water with complete diastereoselectivity. This discovery provides an environmentally friendly way to generate carbonyl ylide dipoles and to synthesize substituted spiro-heterocycles in water with stereoselectivity, avoiding the use of toxic halogenated organic solvents.

ChemInform Abstract: Aza‐[4 + 3] and Aza‐[3 + 2] Annulations for Synthesis of Dihydroazepines and Dihydropyrroles from Alkynes, Sulfonyl Azides, and 1,3‐Dienes.

AbstractThe reaction of triazole (I) with dienes (II) and (VI) in the presence of rhodium(II) octanoate as catalyst leads to dihydropyrroles (III) and (VII), resp., whilst the Rh2((S)‐PTAD)4‐catalyzed reaction affords dihydroazepines (V).

Highly Efficient Synthesis of Conformationally Fixed Bicyclo[3.1.0]hexyl Nucleosides with an Ethenyl Group at C3'-Position as Potential Antiviral Agents

Synthesis of north-5′-methylbicyclo[3.1.0]hexyl adenine and hypoxanthine nucleosides with an ethenyl group at C3′ position was successfully achieved by a highly facile method. Methylbicyclo[3.1.0]hexanone (±)-7 with three contiguous chiral centers and its epimer (±)-6 was remarkably simply constructed only by four steps involving a carbenoid insertion reaction in the presence of rhodium (II) acetate dimer as a metal catalyst, giving a correct relative stereochemistry of the generated three chiral centers. Due to steric hindrance from the concave face of the bicyclo[3.1.0]hexanone system, a Grignard reaction of (±)-7 with ethenylmagnesium bromide showed exclusive diastereoselectivity towards the b-face. The Grignard reaction chemoselectively proceeded without reacting with ester functionality. Coupling reaction of glycosyl donor (±)-11 with 6-chloropurine nucleobase afforded only the desired N-alkylated nucleoside without the formation of N-regioisomer. By the conventional method, 6-chloro group was converted into 6-amino and 6-hydroxy groups to give the desired adenine and hypoxanthine bicyclo[3.1.0]hexyl carbanucleosides with 3′-ethenyl group, respectively.

Rhodium(II) catalyzed highly diastereoselective synthesis of conformationally restricted dispiro[1,3-dioxolane]bisoxindoles

Synthesis of conformationally restricted dispiro- and bis-dispiro-1,3-dioxolanes via three-component reaction of diazoamides, ketoamides/diketones, and aromatic/heteroaromatic aldehydes in the presence of rhodium(II) acetate dimer catalyst at room temperature involving carbonyl ylides is demonstrated with diastereoselectivity. Synthesis of macrocyclic dispiro-1,3-dioxolanes via intramolecular carbonyl ylide is also delineated in high yield. The conformationally restricted symmetrical as well as unsymmetrical dispiro-1,3-dioxolanes were obtained under mild conditions in a highly diastereo- and regioselective manner.