In Rhodium Research Articles

Catalyst Loading Controls Chemoselectivity: Unusual Effect in Rhodium(II) Carbene Insertion Reactions with Tetrahydrofuran

(E)-3-Arylidene-4-diazopyrrolidine-2,5-diones previously shown to yield two products in reactions with tetrahydrofuran mediated by rhodium carbenes—tetrahydrofur-2-yl-substituted product of C-H insertion and spirocyclic product of formal C-O insertion. Accidentally, it was noted that the ratio of the two products depends on the catalyst loading, and the phenomenon was investigated in detail. It was found to be of preparative significance: by solely changing the catalyst loading from 0.01 mol% to 10 mol%, one can obtain sound yields of either of the two products. Mechanistic and kinetic interpretation of this new phenomenon has been proposed.

Ammonia Capture in Rhodium(II)-Based Metal-Organic Polyhedra via Synergistic Coordinative and H-Bonding Interactions.

Ammonia (NH3) is among the world's most widely produced bulk chemicals, given its extensive use in diverse sectors such as agriculture; however, it poses environmental and health risks at low concentrations. Therefore, there is a need for developing new technologies and materials to capture and store ammonia safely. Herein, we report for the first time the use of metal-organic polyhedra (MOPs) as ammonia adsorbents. We evaluated three different rhodium-based MOPs: [Rh2(bdc)2]12 (where bdc is 1,3-benzene dicarboxylate); one functionalized with hydroxyl groups at its outer surface [Rh2(OH-bdc)2]12 (where OH-bdc is 5-hydroxy-1,3-benzene dicarboxylate); and one decorated with aliphatic alkoxide chains at its outer surface [Rh2(C12O-bdc)2]12 (where C12O-bdc is 5-dodecoxybenzene-1,3-benzene dicarboxylate). Ammonia-adsorption experiments revealed that all three Rh-MOPs strongly interact with ammonia, with uptake capacities exceeding 10 mmol/gMOP. Furthermore, computational and experimental data showed that the mechanism of the interaction between Rh-MOPs and ammonia proceeds through a first step of coordination of NH3 to the axial site of the Rh(II) paddlewheel cluster, which triggers the adsorption of additional NH3 molecules through H-bonding interaction. This unique mechanism creates H-bonded clusters of NH3 on each Rh(II) axial site, which accounts for the high NH3 uptake capacity of Rh-MOPs. Rh-MOPs can be regenerated through their immersion in acidic water, and upon activation, their ammonia uptake can be recovered for at least three cycles. Our findings demonstrate that MOPs can be used as porous hosts to capture corrosive molecules like ammonia, and that their surface functionalization can enhance the ammonia uptake performance.

Dual Catalysis in Rhodium(II) Carbenoid Chemistry

AbstractDual catalysis represents an alternative archetype in carbene chemistry that surpasses traditional single catalyst systems. By employing dual catalyst systems, one can improve the efficiency of existing reactions and enable new chemical transformations. Reactions involving dual synergistic catalysis are increasingly valuable as they offer convenient strategies for synthesizing challenging quaternary carbon centers and bioactive core structures. This review article focuses on trapping diazo‐derived, rhodium (II) zwitterionic intermediates with varying electrophiles such as Michael acceptors, alkynes, π‐allyl Pd(II) complexes, and the Nicholas intermediate.

Relative Reactivity of Stable Ligated Boranes and a Borohydride Salt in Rhodium(II)-Catalyzed Boron-Hydrogen Insertion Reactions.

Relative reactivities of a series of neutral ligated boranes L-BH3 (where L is NHC, amine, pyridine, or phosphine) and the cyanoborohydride anion have been assessed in Rh(II)-catalyzed B-H insertion reactions with methyl 2-phenyl-2-diazoacetate. Stable α-boryl ester products were isolated by flash chromatography in all cases except for the salt product from cyanoborohydride. All of the substrates were either comparable to or more reactive than 1,4-cyclohexadiene, which is one of the most reactive substrates in C-H insertion reactions. The range of reactivity between the most reactive pyridine-borane and the least reactive phosphine-borane is a factor of approximately 40.

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations

Complexation of tetrakis(μ2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using (1)H, (13)C and (15)N NMR, (13)C and (15)N cross polarisation-magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1 , and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of (1)H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters.

The Bis(trimethylsilyl)methyl Group as an Effective N-Protecting Group and Site-Selective Control Element in Rhodium(II)-Catalyzed Reaction of Diazoamides

The intramolecular rhodium(II)-carbenoid-mediated C-H insertion reaction of structurally varied N-bis(trimethylsilyl)methyl,N-substituted diazoamides is studied. It has been found that in tertiary diazoamides the N-bis(trimethylsilyl)methyl (N-BTMSM) group is effective for conformational control about the amide N-C(O) bond; C-H insertion occurs at the other N-substituent. In C(alpha)-branched diazoamides, the N-BTMSM is found also to exert its influence on the conformational preference about the N-C(alpha) bond, which affects the regioselectivity of the C-H insertion in these systems. In unbranched diazoamides, inherent electronic effects of the N-substituent affect the regio- and chemoselectivity of the reaction; however, in branched diazoamides, electronic effects of the N-substituent and the alpha-substituent at the carbenoid carbon are subtle, but important in the deciding the eventual outcome of the reaction.

Fluorinated Diazo Diketones in Rhodium(II)‐Catalyzed Reactions with Sultams: Chemoselective O‐Functionalization of Amide Carbonyl Groups

AbstractRhodium(II)‐catalyzed decomposition of fluorinated diazo diketones in the presence of isothiazole‐3(2H)‐one 1,1‐dioxides offers a chemoselective and useful tool for O‐functionalization of their CO groups by interaction with transient fluorine‐containing RhII‐diketocarbenoids. The resulting O‐alkylimidates of isothiazole 1,1‐dioxides, bearing (trifluoromethyl)acetyl groups, easily react with traces of H2O giving rise to stable hydrates of the perfluoroacetyl groups. No O→N isomerization of O‐alkylimidates (similar to the Lander–Chapman rearrangement) was observed under the reaction conditions studied.

Coordination chemistry of buckybowls: from corannulene to a hemifullerene

This work highlights the progress made in coordination chemistry of transition-metal centers to open geodesic polyaromatic hydrocarbons that map onto the surface of C60, the family of compounds known as buckybowls or 'fullerene fragments'. In particular, an overview of our recent gas-phase coordination studies of several bowl-shaped polyarenes toward the dinuclear metal complex, [Rh2(O2CCF3)4], is given. Selected buckybowls include corannulene (C20H10) and two of its derivatives, namely dibenzo[a,g]corannulene (C28H14) and 1,3,5,7,9-penta-tert-butylcorannulene (C40H50), as well as a hemifullerene (C30H12). This study has resulted in the first X-ray structural characterization of buckybowl coordination complexes and has revealed eta2-rim coordination preferences of open geodesic polyarenes in rhodium(ii) binding reactions.

Selectivity in Rhodium(II) Catalyzed Reactions of Diazo Compounds: Effects of Catalyst Electrophilicity, Diazo Substitution, and Substrate Substitution. From Chemoselectivity to Enantioselectivity

AbstractFor Abstract see ChemInform Abstract in Full Text.

Selectivity in Rhodium(II)Catalyzed Reactions of Diazo Compounds: Effects of Catalyst Electrophilicity,Diazo Substitution, and Substrate Substitution. From Chemoselectivityto Enantioselectivity

Rhodium catalyzed reactions of diazo compounds form a powerful set of tools for synthetic organic chemists. Reactivity modes include cyclopropanation, C-H insertion, X-H insertion, and ylide formation. A myriad of factors influences the mode of reaction, selectivity, and yield for these reaction processes. This review examines the subtle electronic, steric and conformational effects that in turn have profound impacts on reaction paths and selectivity.

ChemInform Abstract: Reactivity of Differentially Substituted Bis(diazo) Esters in Rhodium(II) Mediated O—H Insertion Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reactivity of differentially substituted bis(diazo) esters in rhodium(II) mediated O-H insertion reactions

Selective catalysed decompositions of one diazo group in the presence of another are discussed. A range of bis(diazo) compounds was prepared in which the two diazo groups are differentially substituted. Rhodium(II) acetate catalysed decomposition in the presence of methanol resulted in exclusive O-H insertion reaction at the more reactive diazo group, the less reactive diazophosphonate remaining intact. With the more active rhodium(II) trifluoroacetamide as catalyst, both diazo groups decomposed simultaneously.

Selectivity in Rhodium(II)‐Catalyzed Rearrangements of cycloprop‐2‐ene‐1‐carboxylates

AbstractThe course of the thermocatalytic rearrangement of cycloprop‐2‐ene‐1‐carboxylates in the presence of dirhodium(II) tetrakis(perfluorobutyrate) ([Rh2(pfb)4]) was investigated by varying the substituents of the cyclopropene ring. Product composition is markedly influenced by the number, nature, and position of the substituents, which determine the regio‐ and stereoselectivity of the cyclopropene‐ring cleavage. A mechanism is proposed in which attack of the electrophilic RhII species is concerted with disrotatory ring opening of the incipient cyclopropyl cation and affords a metal‐complexed vinylcarbene. The chemoselectivity of the latter is consistent with that of other carbenes generated in the presence of [Rh2(pfb)4].

ChemInform Abstract: Carbenoid versus Vinylogous Reactivity in Rhodium(II)‐Stabilized Vinylcarbenoids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Highly Selective Insertion into Aromatic C‐H Bonds in Rhodium(II) Triphenylacetate‐Catalyzed Decomposition of α‐Diazocarbonyl Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: α‐Hydroxy Esters as Inexpensive Chiral Auxiliaries in Rhodium(II) ‐Catalyzed Cyclopropanations with Vinyldiazomethanes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

α-hydroxy esters as inexpensive chiral auxiliaries in rhodium(II)-catalyzed cyclopropanations with vinyldiazomethanes

High levels of asymmetric induction were achieved in rhodium(II) catalyzed cyclopropanations with chiral vinyldiazomethanes. (R)-(−)-Pantolactone is the most effective chiral auxiliary, but other α-hydroxy esters also give reasonable levels of diastereoselectivity.

ChemInform Abstract: Synthesis of Allenes by (2,3)Sigmatropic Rearrangement of Prop‐2‐yn‐1‐yloxonium Ylides Formed in Rhodium(II) Carboxylate Catalyzed Reactions of Diazo Compounds.

ChemInform Abstract: Synthesis of Allenes by (2,3)Sigmatropic Rearrangement of Prop‐2‐yn‐1‐yloxonium Ylides Formed in Rhodium(II) Carboxylate Catalyzed Reactions of Diazo Compounds.

ChemInform Abstract: Conformation and Electronic Preferences in Rhodium(II) Carboxylate and Rhodium(II) Carboxamide‐Catalyzed Carbon‐Hydrogen Insertion Reactions of N,N‐Disubstituted Diazoacetoacetamides.

AbstractThe N‐(3‐ethoxycarbonylethyl) α‐azo β‐keto amides (I), (III), and (VII) are denitrogenated in the presence of rhodium catalysts to undergo cyclization, producing the β‐lactams (II), (IV), or (VIII), the pyrrolidinones (V) or (IX), and the oxazepinones (VI) or (X).

Synthesis of allenes by [2,3]-sigmatropic rearrangement of prop-2-yn-1-yl oxonium ylides formed in rhodium(II) carboxylate catalysed reactions of diazo compounds

High oxophilicity of metal carbenes formed in rhodium(II) perfluorobutyrate catalysed decomposition of diazo carbonyl compounds allows selective ylide generation from methyl prop-2-yn-1-yl ethers with resulting allene production through the [2,3]-sigmatropic rearrangement.