Rhodium Carboxylate Research Articles

Complex formation of rhodium(II) carboxylate with cis-dinitrodibenzo-18-crown-6 and cis-diaminodibenzo-18-crown-6 in ethanol

Chemical properties of crown ethers with functional groups have been intensively studied over the past years in view of the possibility of synthesis of compounds playing important roles in catalytic and biological processes. Binuclear carboxylale complexes of Rh(II) [1] are highly active in hydroformylation and oxidation reactions, as well as antitumor drugs that act similarly to Pt(II) cis-diammine complexes. In this connection we have studied the reactions of Rh2 (CH3COO)4 (I) with cis-dinitrodibenzo-18-crown-6 (L) and cis-diaminodibenzo-18-crown-6 (L) in absolute ethanol. Preliminary operations and synthesis were carried out using Schlenk technique under dry argon or in a vacuum. Compound I was prepared by the procedure in [2], and before use it was heated in a vacuum for 20 30 min at its sublimation initiation point. Compounds L and L were obtained according to [3] and dried by zeolites before use.

Rh‐Catalyzed Transannulation of Pyridotriazoles with Alkynes and Nitriles.

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Rh-catalyzed transannulation of pyridotriazoles with alkynes and nitriles.

Rh-catalyzed transannulation of pyridotriazoles with alkynes and nitriles.

Tuning the Properties at Heterobimetallic Core: Mixed-Ligand Bismuth−Rhodium Paddlewheel Carboxylates

Mixed-ligand heterometallic compounds [BiRh(O2CCF3)4-x(O2CR)x] (R = But, x = 2 (cis); R = Me, Bui, x = 1) have been obtained by gas-phase reactions of bismuth(II) trifluoroacetate with the corresponding rhodium(II) carboxylate. This synthetic approach was found to be very effective for tuning the properties and introduction of chiral ligands at a heterobimetallic core.

Diastereoselective rhodium-catalyzed nitrene transfer starting from chiral sulfonimidamide-derived iminoiodanes

The dirhodium-catalyzed aziridination of olefins with chiral sulfonimidamides as iminoiodane precursors has been investigated under stoichiometric conditions. Diastereoisomeric excesses of up to 82% have been achieved using [Rh 2{( S)-nttl} 4] as catalyst. Matching and mismatching effects were observed upon use of chiral rhodium(II) carboxylate catalysts.

Novel microporous rhodium(II) carboxylate polymer complexes containing metalloporphyrin: syntheses and catalytic performances in hydrogenation of olefins

Novel microporous rhodium(II) carboxylate polymer complexes containing metalloporphyrin, Rh 2[MTCPP] (M = H 2 1, Cu 2+ 2, Ni 2+ 3, Pd 2+ 4) (H 2TCPP = 4,4′,4″,4′″-(21 H,23 H-porphine-5,10,15,20-tetrayl)tetrakis benzoic acid), were synthesized and completely characterized by elemental analysis, TG/DTA, magnetic susceptibilities, FT-IR, DR-UV–vis, XRPD, BET analysis, and nitrogen adsorption measurements. These complexes possess carboxylate bridged dinuclear rhodium(II) sites and mononuclear copper(II), nickel(II), and palladium(II) centers in the porphyrin ring that form uniform micropores of ca. 5.0 Å. Furthermore, they show high surface areas and high nitrogen adsorption capacities and act as efficient heterogeneous catalysts for the hydrogenation of olefins at approximately 200 K. The unique bimetallic effects shown by metalloporphyrin and dinuclear rhodium sites in micropores were investigated by kinetic studies and hydrogen and propene adsorption–desorption measurements; the priority coordination of olefins onto metalloporphyrins and the intramolecular transfer of hydrogen from a rhodium center to a olefin molecule coordinated onto metalloporphyrin remarkably reflects the catalytic activities in hydrogenation.

Ring Expansion-Annulation Strategy for the Synthesis of Substituted Azulenes and Oligoazulenes. 2. Synthesis of Azulenyl Halides, Sulfonates, and Azulenylmetal Compounds and Their Application in Transition-Metal-Mediated Coupling Reactions

A "ring expansion-annulation strategy" for the synthesis of substituted azulenes is described based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates. The key transformation involves an intramolecular Buchner reaction followed by beta-elimination of bromide, tautomerization, and in situ trapping of the resulting 1-hydroxyazulene as a carboxylate or triflate ester. Further synthetic elaboration of the azulenyl halide and sulfonate annulation products can be achieved by employing Heck, Negishi, Stille, and Suzuki coupling reactions. Reaction of the azulenyl triflate 84 with pinacolborane provides access to the azulenylboronate 91, which participates in Suzuki coupling reactions with alkenyl and aryl iodides. The application of these coupling reactions to the synthesis of biazulenes, terazulene 101, and related oligoazulenes is described, as well as the preparation of the azulenyl amino acid derivative 110.

Scalar Relativistic Study of the Structure of Rhodium Acetate

Rhodium acetate, related rhodium carboxylates, and rhodium amide complexes are powerful catalysts for carbene chemistry. They readily promote the decomposition of diazo compounds and transfer the resulting carbene to a variety of substrates. There have been several quantum chemistry studies of these compounds, particularly of the acetate. These have all used non-relativistic methods, and all have shown optimized Rh-Rh bond lengths significantly longer than the experimental value. In this study we have surveyed several scalar relativistic DFT methods using Gaussian, Slater, and numerical basis functions (in DGAUSS, ADF, and DMOL3). Several combinations of exchange-correlation functionals with relativistic and non-relativistic effective core potentials (ECP) were investigated, as were non-relativistic and all electron scalar relativistic methods. The combination of the PW91 exchange and PW91 correlation functional with the Christiansen-Ermler ECP gave the best results: 2.3918 Å compared to the experimental value of 2.3855±0.0005 Å.

Rhodium Carbenoid N—H Insertion Reactions of Primary Ureas: Solution and Solid‐Phase Synthesis of Imidazolones.

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Rhodium carbenoid N-H insertion reactions of primary ureas: solution and solid-phase synthesis of imidazolones.

[reaction: see text] The solution and solid-phase synthesis of imidazolones is reported. The key step for the preparation of these compounds is the N-H insertion reaction of primary ureas into highly reactive rhodium carbenoid intermediates. Typically, a soluble or support-bound alpha-diazo-beta-ketoester is treated with a rhodium carboxylate catalyst in the presence of a primary urea to give the corresponding N-H insertion product. Subsequent acid-catalyzed cyclodehydration of these insertion products affords the desired imidazolone products.

Rhodium Carboxylate Catalyzed Decomposition of Vinyldiazoacetates in the Presence of Heterodienes: Enantioselective Synthesis of the 6‐Azabicyclo[3.2.2]nonane and 6‐Azabicyclo[3.2.2]nonanone Ring Systems.

Dirhodium tetracarboxylate catalyzed decomposition of vinyldiazoacetates in the presence of N-phenoxycarbonyl protected 1,2-dihydropyridines or 1-methyl-2-pyridones is a direct method for the construction of the 6-azabicyclo[3.2.2]nonane ring system. The [3 + 4] cycloaddition occurs by a tandem cyclopropanation/Cope rearrangement. Asymmetric induction is possible in these transformations either by using (S)-lactate methyl ester as a chiral auxiliary or dirhodium tetraprolinates as chiral catalysts.

Rhodium carboxylate catalyzed decomposition of vinyldiazoacetates in the presence of heterodienes: enantioselective synthesis of the 6-azabicyclo[3.2.2]nonane and 6-azabicyclo[3.2.2]nonanone ring systems.

Dirhodium tetracarboxylate catalyzed decomposition of vinyldiazoacetates in the presence of N-phenoxycarbonyl protected 1,2-dihydropyridines or 1-methyl-2-pyridones is a direct method for the construction of the 6-azabicyclo[3.2.2]nonane ring system. The [3 + 4] cycloaddition occurs by a tandem cyclopropanation/Cope rearrangement. Asymmetric induction is possible in these transformations either by using (S)-lactate methyl ester as a chiral auxiliary or dirhodium tetraprolinates as chiral catalysts.

A pyrazine bis-adduct of a binuclear rhodium(II) carboxylate containing 3,4,5-triethoxybenzoate as the equatorial ligand.

The title compound, tetrakis(mu-3,4,5-triethoxybenzoato-kappa(2)O:O')bis[(pyrazine-kappa N)rhodium(II)](Rh[bond]Rh), [Rh(2)(C(13)H(17)O(5))(4)(C(4)H(4)N(2))(2)], crystallizes on an inversion centre in the triclinic space group P1. The equatorial carboxylate ligands bridge the two Rh(II) atoms, giving a binuclear lantern-like structure. The pyrazine molecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10 degrees with respect to the attached carboxylate groups. The pyrazine planes have a torsion angle of ca 19 degrees around the Rh-N bond with respect to the plane of the nearer carboxylate group and are not coplanar with the Rh[bond]Rh bond.

Liquid-Crystalline Materials Based on Rhodium Carboxylate Coordination Polymers: Synthesis, Characterization and Mesomorphic Properties of Tetra(alkoxybenzoato)dirhodium(II) Complexes and Their Pyrazine Adducts

Tetra(alkoxybenzoato)dirhodium(II) complexes of the formula Rh2(x,y,z-BmOCn)4 (where B is the benzoate group; m is the number of alkoxy chains on the aromatic ring; x, y, and z are their positions of anchoring; and n is the number of carbon atoms in each alkoxy chain) and the corresponding pyrazine adducts have been synthesized and characterized. The pyrazine adducts were prepared to have a polymeric structure via connected metallic centers. The complexes synthesized are Rh2(3,4,5-B3OCn)4 for n = 8, 10, 14, and 18; Rh2(3,4-B2OCn)4 for n = 9, 14, and 18; and Rh2(3,5-B2OCn)4 for n = 9 and 18, as well as the corresponding pyrazine adducts [Rh2(3,4,5-B3OCn)4pz]x for n = 10, 14, and 18; [Rh2(3,4-B2OCn)4pz]x for n = 14 and 18; and [Rh2(3,5-B2OCn)4pz]x for n = 9 and 18. Their liquid-crystalline (LC) properties have been analyzed. Most of them exhibit LC columnar and cubic mesophases with melting transition temperatures close to or even below room temperature. The mesomorphic character of the pyrazinic compounds, compared to the nonmesomorphic aliphatic carboxylate analogues, can be interpreted in terms of the ability of the equatorial ligands to fill the interdimeric space efficiently. Some internal characteristics about the arrangement of the molecules inside the columns are discussed.

Rhodium Chemzymes: Michaelis−Menten Kinetics in Dirhodium(II) Carboxylate-Catalyzed Carbenoid Reactions

Rhodium carboxylate-mediated reactions of diazoketones involving cyclopropanation, C-H insertion, and aromatic C-C double bond addition/electrocyclic ring opening obey saturation (Michaelis-Menten) kinetics. Axial ligands for rhodium, including aromatic hydrocarbons and Lewis bases such as nitriles, ethers, and ketones, inhibit these reactions by a mixed kinetic inhibition mechanism, meaning that they can bind both to the free catalyst and to the catalyst-substrate complex. Substrate inhibition can also be exhibited by diazocompounds bearing these groupings in addition to the diazo group. The analysis of inhibition shows that the active catalyst uses only one of its two coordination sites at a time for catalysis. Some ketones exhibit the interesting property that they selectively bind to the catalyst-substrate complex. The similarity of the kinetic constants from different types of reactions with similar diazoketones, regardless of the linking unit or the environment of the reacting alkene, suggests that the rate-determining step is the generation of the rhodium carbenoid. A very useful rhodium carboxylate catalyst for asymmetric synthesis, Rh(2)(DOSP)(4), shows slightly slower kinetic parameters than the achiral catalysts, implying that enantioselectivity of this catalyst is based on slowing reactions from one of the enantiotopic faces of the reactant, rather than any type of ligand-accelerated catalysis. A series of rhodium catalysts derived from acids with pK(a)s spanning 4 orders of magnitude give very similar kinetic constants.

Controlled release of rhodium (II) carboxylates and their association complexes with cyclodextrins from hydroxyapatite matrix

Preparation and characterization of a controlled release system of rhodium (II) citrate, acetate, propionate, butyrate and their inclusion or association compounds with cyclodextrin (CD) are described. The porous hydroxyapatite (HA) was characterized by X-ray powder pattern diffraction, FTIR and solid state 31P NMR. Scanning electron microscopy and gas adsorption analysis (BET) were also performed. Release profiles of rhodium (II) carboxylates and their inclusion or association compounds from HA matrix were obtained at different drug loadings (5% and 10%). These were reasonably consistent with a diffusion model. This analysis, mainly using rhodium (II) citrate and butyrate, showed that the strategy of using CDs with a HA matrix may offer a useful new method for the controlled release of these compounds, and hence an alternative strategy for the controlled release of chemotherapeutic agents containing toxic metals. This may be a valuable new technique for localized anti-tumour chemotherapy that minimizes the side effects of such agents.

Electrochemical evaluation of rhodium dimer-DNA interactions

The interaction of rhodium dimers, including the carboxylates (acetate, propionate, butyrate, trifluoroacetate, citrate and gluconate), amidates (acetamidate and trifluoroacetamidate) and carboxamidate (Doyle catalyst S) with DNA was investigated by electrochemical methods. Differential pulse voltammetry measurements showed, in agreement to literature data, that most of rhodium carboxylates have a higher affinity for adenine than guanine residues. Some differences of reactivity may be correlated with the compound structures and these were helpful in understanding the influence of equatorial ligands on axial coordination mechanisms. The preliminary results might be extended for further studies on quantitative structure activity relationship approaches, highlighting electrochemical methods as a tool for this purpose.

Dynamic equilibria in the products of intramolecular Buchner additions of diazoketones to aryl rings bearing methoxy substituents.

Rhodium carboxylate catalyzed aromatic addition reactions of a range of diazoketones bearing methoxy-substituted aryl rings have been explored. While the existence of norcaradiene-cycloheptatriene equilibria in related compounds is well established, the aromatic addition products in this study display more complex dynamic equilibria due to conjugation with the methoxy group; the experimental evidence for this is discussed in detail. In the azulenone products 21-26 derived from p-methoxy-substituted diazoketones 14-16, the diastereomers interconvert via a spiro intermediate 39. A related mechanistic process in the azulenones 43-46 derived from the o-methoxy-substituted diazoketones 17, 18 interconverts regioisomers, explaining the conflicting reports for the regioselectivity of the cyclization of diazoketone 1. With the m-methoxy-substituted diazoketone 19, involvement of the methoxy group through a different pathway results in fragmentation of the azulenone to form the tetralone 47. With the azulenones 21-26 exclusive trapping of the norcaradiene associated with the less thermodynamically stable diastereomers in a cycloadduct with N-phenylmaleimide is observed. Due to the presence of the activating methoxy substituent on the aromatic ring, the aromatic addition reactions of the diazoketones studied were not very sensitive to the nature of the rhodium catalyst.

A ring expansion-annulation strategy for the synthesis of substituted azulenes. Preparation and Suzuki coupling reactions of 1-azulenyl triflates.

[structure: see text]. A new strategy for the synthesis of substituted azulenes is reported, based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates. The key transformation involves intramolecular addition of a rhodium carbenoid to an arene pi-bond, electrocyclic ring opening, beta-elimination, tautomerization, and trapping to produce 1-hydroxyazulene derivatives. The synthetic utility of the method is enhanced by the ability of the triflate derivatives to participate in Suzuki coupling reactions, as illustrated in a synthesis of the antiulcer drug egualen sodium (KT1-32).

Cyclization-cycloaddition casade of rhodium carbenoids using different carbonyl groups. Highlighting the position of interaction

A series of 3-diazoalkanediones, when treated with a catalytic quantity of a rhodium(II) carboxylate, were found to afford oxabicyclic dipolar cycloadducts derived by the trapping of a carbonyl ylide intermediate. The reaction involves generation of the 1,3-dipole by intramolecular cyclization of the keto carbenoid onto the oxygen atom of the neighboring keto group. Both five- and six-ring carbonyl ylides are formed with the same efficiency. A study of the tandem cyclization-cycloaddition cascade of several alpha-diazo ketoesters was also carried out, and the cascade sequence proceeded in high yield. When the interacting keto carbonyl group was replaced by an imido group, the rhodium(II)-catalyzed reaction proceeded uneventfully. In contrast, alpha-diazo amidoesters do not undergo nitrogen extrusion on treatment with a Rh(II) catalyst. Instead, the diazo portion of the molecule undergoes 1,3-dipolar cycloaddition with various dipolarophiles to give substituted pyrazoles as the final products.