Rhodium-Catalyzed Arene Alkenylation: Selectivity and Reaction Mechanism as a Function of In Situ Oxidant Identity.

Rhodium catalyzed arene alkenylation reactions with arenes and olefins using dioxygen as the direct oxidant (e.g., , , 11519), Cu(II) carboxylates (e.

Synthesis of Quinoline-Based Pt-Sb Complexes with L- or Z-Type Interaction: Ligand-Controlled Redox via Anion Transfer.

A series of Pt-Sb complexes with two or three L-type quinoline side arms were prepared and studied. Two ligands, tri(8-quinolinyl)stibane (SbQ, Q = 8-quinolinyl, ) and 8,8'-(phenylstibanediyl)diquinoline (SbQPh, ), were used to synthesize the Pt-Sb complexes (SbQ)PtCl () and (SbQPh)PtCl (). Chloride abstraction with AgOAc provided the bis-acetate complexes (SbQ)Pt(OAc) () and (SbQPh)Pt(OAc) ().

Carbodicarbene-Stibenium Ion-Mediated Functionalization of C(sp)-H and C(sp)-H Bonds.

Main-group element-mediated C-H activation remains experimentally challenging and the development of clear concepts and design principles has been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(CDC)Sb][NTf] (1) (CDC=bis-pyridyl carbodicarbene; NTf=bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6-di-tert-butylpyridine to enable C(sp)-H bond breaking to generate the stiba-methylene nitrile complex [(CDC)Sb(CHCN)][NTf] (2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction.

Hexa-Fe(III) Carboxylate Complexes Facilitate Aerobic Hydrocarbon Oxidative Functionalization: Rh Catalyzed Oxidative Coupling of Benzene and Ethylene to Form Styrene.

Fe(II) carboxylates react with dioxygen and carboxylic acid to form Fe(μ-OH)(μ-O)(μ-X)(HX) (X = acetate or pivalate), which is an active oxidant for Rh-catalyzed arene alkenylation. Heating (150-200 °C) the catalyst precursor [(η-CH)Rh(μ-OAc)] with ethylene, benzene, Fe(II) carboxylate, and dioxygen yields styrene >30-fold faster than the reaction with dioxygen in the absence of the Fe(II) carboxylate additive. It is also demonstrated that Fe(μ-OH)(μ-O)(μ-X)(HX) is an active oxidant under anaerobic conditions, and the reduced material can be reoxidized to Fe(μ-OH)(μ-O)(μ-X)(HX) by dioxygen.

Rhodium-Catalyzed Oxidative Alkenylation of Anisole: Control of Regioselectivity.

We report the conversion of anisoles and olefins to alkenyl anisoles via a transition-metal-catalyzed arene C-H activation and olefin insertion mechanism. The catalyst precursor, [(η-CH)Rh(μ-OAc)], and the in situ oxidant Cu(OPiv) (OPiv = pivalate) convert anisoles and olefins (ethylene or propylene) to alkenyl anisoles. When ethylene is used as the olefin, the // ratio varies between approximately 1:3:1 (selective for 3-methoxystyrene) and 1:5:10 (selective for 4-methoxystyrene).

Highly Anti-Markovnikov Selective Oxidative Arene Alkenylation Using Ir(I) Catalyst Precursors and Cu(II) Carboxylates.

The Ir(I) complex [Ir(μ-Cl)(coe)] (coe = cyclooctene) is a catalyst precursor for benzene alkenylation using Cu(II) carboxylate salts. Using [Ir(μ-Cl)(coe)], propenylbenzenes are formed from the reaction of benzene, propylene, and CuX (X = acetate, pivalate, or 2-ethylhexanoate). The Ir-catalyzed reactions selectively produce anti-Markovnikov products, -β-methylstyrene, -β-methylstyrene, and allylbenzene, along with minor amounts of the Markovnikov product, α-methylstyrene.

Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel-Boron Cooperativity in a PBP-Ni Complex.

The synthesis and characterization of ( PBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni-C bond of ( PBP)NiMe (1) is presented. An unexpected CO cleavage process involving the formation of new B-O and Ni-CO bonds leads to the generation of a butterfly-structured tetra-nickel cluster ( PBOP) Ni (μ-CO) (6). Mechanistic investigation of this reaction indicates a reductive scission of CO by O-atom transfer to the boron atom via a cooperative nickel-boron mechanism.

Pd(II) and Rh(I) Catalytic Precursors for Arene Alkenylation: Comparative Evaluation of Reactivity and Mechanism Based on Experimental and Computational Studies.

We combine experimental and computational investigations to compare and understand catalytic arene alkenylation using the Pd(II) and Rh(I) precursors Pd(OAc) and [(η-CH)Rh(μ-OAc)] with arene, olefin, and Cu(II) carboxylate at elevated temperatures (>120 °C). Under specific conditions, previous computational and experimental efforts have identified heterotrimetallic cyclic PdCu(η-CH)(μ-OPiv) and [(η-CH)Rh(μ-OPiv)](μ-Cu) (OPiv = pivalate) species as likely active catalysts for these processes. Further studies of catalyst speciation suggest a complicated equilibrium between Cu(II)-containing complexes containing one Rh or Pd atom with complexes containing two Rh or Pd atoms.

Ethylene Dimerization and Oligomerization Using Bis(phosphino)boryl Supported Ni Complexes.

We report the dimerization and oligomerization of ethylene using bis(phosphino)boryl supported Ni(II) complexes as catalyst precursors. By using alkylaluminum(III) compounds or other Lewis acid additives, Ni(II) complexes of the type (PBP)NiBr (R = Bu or Ph) show activity for the production of butenes and higher olefins. Optimized turnover frequencies of 640 mol·mol·s for the formation of butenes with 41(1)% selectivity for 1-butene using (PBP)NiBr, and 68 mol·mol·s for butenes production with 87.

Cu(II) carboxylate arene C─H functionalization: Tuning for nonradical pathways.

We report carbon-hydrogen acetoxylation of nondirected arenes benzene and toluene, as well as related functionalization with pivalate and 2-ethylhexanoate ester groups, using simple copper(II) [Cu(II)] salts with over 80% yield. By changing the ratio of benzene and Cu(II) salts, 2.4% conversion of benzene can be reached.

Aerobic Partial Oxidation of Alkanes Using Photodriven Iron Catalysis.

Photodriven oxidations of alkanes in trifluoroacetic acid using commercial and synthesized Fe(III) sources as catalyst precursors and dioxygen (O) as the terminal oxidant are reported. The reactions produce alkyl esters and occur at ambient temperature in the presence of air, and catalytic turnover is observed for the oxidation of methane in a pure O atmosphere. Under optimized conditions, approximately 17% conversion of methane to methyl trifluoroacetate at more than 50% selectivity is observed.

Advances in Group 10 Transition-Metal-Catalyzed Arene Alkylation and Alkenylation.

On a large scale, the dominant method to produce alkyl arenes has been arene alkylation from arenes and olefins using acid-based catalysis. The addition of arene C-H bonds across olefin C═C bonds catalyzed by transition-metal complexes through C-H activation and olefin insertion into metal-aryl bonds provides an alternative approach with potential advantages. This Perspective presents recent developments of olefin hydroarylation and oxidative olefin hydroarylation catalyzed by molecular complexes based on group 10 transition metals (Ni, Pd, Pt).

Reductive C-C Coupling from Molecular Au(I) Hydrocarbyl Complexes: A Mechanistic Study.

Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C-C bond formation. In this study, we investigate C-C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au(μ-CH)(PMeAr')][NTf], [Au(μ-CH)(XPhos)][NTf], and [Au(μ-CH)(BuXPhos)][NTf] {Ar' = CH-2,6-(CH-2,6-Me), CH-2,6-(CH-2,4,6-Me), CH-2,6-(CH-2,6-Pr), or CH-2,6-(CH-2,4,6-Pr); XPhos = 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl; BuXPhos = 2-di--butylphosphino-2',4',6'-triisopropylbiphenyl; NTf = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH)L and Au(L)(NTf) {L = phosphines listed above}.

Synthesis of Stilbenes by Rhodium-Catalyzed Aerobic Alkenylation of Arenes via C-H Activation.

Arene alkenylation is commonly achieved by late transition metal-mediated C(sp)-C(sp) cross-coupling, but this strategy typically requires prefunctionalized substrates (e.g., with halides or pseudohalides) and/or the presence of a directing group on the arene.

Advances in Rhodium-Catalyzed Oxidative Arene Alkenylation.

ConspectusAlkyl and alkenyl arenes are of substantial value in both large-scale and fine chemical processes. Billions of pounds of alkyl and alkenyl arenes are produced annually. Historically, the dominant method for synthesis of alkyl arenes is acid-catalyzed arene alkylation, and alkenyl arenes are often synthesized in a subsequent dehydrogenation step.

Generalized Synthetic Strategy for Transition-Metal-Doped Brookite-Phase TiO Nanorods.

We report a generalized wet-chemical methodology for the synthesis of transition-metal (M)-doped brookite-phase TiO nanorods (NRs) with unprecedented wide-range tunability in dopant composition (M = V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc.). These quadrangular NRs can selectively expose {210} surface facets, which is induced by their strong affinity for oleylamine stabilizer.

Catalytic Synthesis of Superlinear Alkenyl Arenes Using a Rh(I) Catalyst Supported by a "Capping Arene" Ligand: Access to Aerobic Catalysis.

Alkyl and alkenyl arenes are used in a wide range of products. However, the synthesis of 1-phenylalkanes or their alkenyl variants from arenes and alkenes is not accessible with current commercial acid-based catalytic processes. Here, it is reported that an air-stable Rh(I) complex, (5-FP)Rh(TFA)(η-CH) (5-FP = 1,2-bis( N-7-azaindolyl)benzene; TFA = trifluoroacetate), serves as a catalyst precursor for the oxidative conversion of arenes and alkenes to alkenyl arenes that are precursors to 1-phenylalkanes upon hydrogenation.

High Selectivity Towards Formate Production by Electrochemical Reduction of Carbon Dioxide at Copper-Bismuth Dendrites.

The electrochemical reduction of CO provides an alternative carbon-neutral path for renewable synthesis of fuels and value-added chemicals. This work demonstrates that dendritic, bimetallic Cu-Bi electrocatalysts with nanometer-sized grains are capable of formate generation with a high selectivity. Optimizing composition of electrocatalyst could achieve a faradic efficiency of 90 % at -0.

Catalytic Synthesis of "Super" Linear Alkenyl Arenes Using an Easily Prepared Rh(I) Catalyst.

Linear alkyl benzenes (LAB) are global chemicals that are produced by acid-catalyzed reactions that involve the formation of carbocationic intermediates. One outcome of the acid-based catalysis is that 1-phenylalkanes cannot be produced. Herein, it is reported that [Rh(μ-OAc)(η-CH)] catalyzes production of 1-phenyl substituted alkene products via oxidative arene vinylation.

Brønsted acid-catalysed intramolecular hydroamination of unactivated alkenes: metal triflates as an in situ source of triflic acid.

Hydroamination of alkenes or alkynes is one of the most straightforward methods to form C-N bonds and nitrogen-containing heterocycles. A simple Lewis acid Al(OTf) was found to be an effective precatalyst for the hydroamination of unactivated primary and secondary alkenylamines between 110 and 150 °C. Subsequent studies show that other metal triflates are also effective precatalysts for the hydroamination reactions.

Mechanistic Studies of Single-Step Styrene Production Using a Rhodium(I) Catalyst.

The direct and single-step conversion of benzene, ethylene, and a Cu(II) oxidant to styrene using the Rh(I) catalyst (DAB)Rh(TFA)(η-CH) [DAB = N,N'-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] has been reported to give quantitative yields (with Cu(II) as the limiting reagent) and selectivity combined with turnover numbers >800. This report details mechanistic studies of this catalytic process using a combined experimental and computational approach. Examining catalysis with the complex (DAB)Rh(OAc)(η-CH) shows that the reaction rate has a dependence on catalyst concentration between first- and half-order that varies with both temperature and ethylene concentration, a first-order dependence on ethylene concentration with saturation at higher concentrations of ethylene, and a zero-order dependence on the concentration of Cu(II) oxidant.

Organometallic Complexes Anchored to Conductive Carbon for Electrocatalytic Oxidation of Methane at Low Temperature.

Low-temperature direct methane fuel cells (DMEFCs) offer the opportunity to substantially improve the efficiency of energy production from natural gas. This study focuses on the development of well-defined platinum organometallic complexes covalently anchored to ordered mesoporous carbon (OMC) for electrochemical oxidation of methane in a proton exchange membrane fuel cell at 80 °C. A maximum normalized power of 403 μW/mg Pt was obtained, which was 5 times higher than the power obtained from a modern commercial catalyst and 2 orders of magnitude greater than that from a Pt black catalyst.

Organic chemistry. A rhodium catalyst for single-step styrene production from benzene and ethylene.

Rising global demand for fossil resources has prompted a renewed interest in catalyst technologies that increase the efficiency of conversion of hydrocarbons from petroleum and natural gas to higher-value materials. Styrene is currently produced from benzene and ethylene through the intermediacy of ethylbenzene, which must be dehydrogenated in a separate step. The direct oxidative conversion of benzene and ethylene to styrene could provide a more efficient route, but achieving high selectivity and yield for this reaction has been challenging.

Partial oxidation of light alkanes by periodate and chloride salts.

The efficient and selective partial oxidation of light alkanes using potassium periodate and potassium chloride is reported. Yields of methane functionalization in trifluoroacetic acid reach >40% with high selectivity for methyl trifluoroacetate. Periodate and chloride also functionalize ethane and propane in good yields (>20%).

Rhodium bis(quinolinyl)benzene complexes for methane activation and functionalization.

A series of rhodium(III) bis(quinolinyl)benzene (bisq(x)) complexes was studied as candidates for the homogeneous partial oxidation of methane. Density functional theory (DFT) (M06 with Poisson continuum solvation) was used to investigate a variety of (bisq(x)) ligand candidates involving different functional groups to determine the impact on Rh(III)(bisq(x))-catalyzed methane functionalization. The free energy activation barriers for methane C-H activation and Rh-methyl functionalization at 298 K and 498 K were determined.