Diene Complexes Research Articles

Experimental and Theoretical Study on the Role of Monomeric vs Dimeric Rhodium Oxazolidinone Norbornadiene Complexes in Catalytic Asymmetric 1,2- and 1,4-Additions

The influence of nuclearity and charge of chiral Rh diene complexes on the activity and enantioselectivity in catalytic asymmetric 1,2-additions of organoboron reagents to N-tosylimines and 1,4-add...

Construction of 1-Tetralols Bearing Two Contiguous Quaternary Chiral Centers through a Rhodium-Catalyzed Enantioselective Desymmetrization Cascade Reaction.

A novel and efficient access to polyfunctionnalized chiral 1-tetralols, bearing two contiguous quaternary carbon stereocenters, has been developed from various and easily accessible alkynyl-1,3-diketones, through a cascade process including a regioselective alkyne insertion, a 1,4-Rh shift, and a nucleophilic addition step via the desymmetrization of the 1,3-diketone moiety thanks to an appropriate rhodium-chiral diene complex in the presence of arylboronic acids.

Pyridine(diimine) Iron Diene Complexes Relevant to Catalytic [2+2]-Cycloaddition Reactions.

The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e- complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI)Fe(η4-piperylene) (Me(Et)PDI = 2,6-(2,6-Me2-C6H3N═CEt)2C5H3N), was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.

Enantioselective Conjugate Addition of Aryl Halides and Triflates to Electron-Deficient Olefins via Nickel- and Rhodium-Catalyzed Sequential Relay Reactions.

Asymmetric conjugate addition of aryl halides or aryl triflates to electron-deficient olefins was realized by sequential Miyaura borylation and Hayashi-Miyaura conjugate addition in one pot. A nickel-catalyzed borylation of aryl halides or triflates and a rhodium-chiral diene complex catalyzed enantioselective conjugate addition was executed as a pair of relay reactions as a more efficient and greener protocol.

Frontispiece: Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium–Diene Complexes in Microemulsions and Conventional Solvents

Frontispiece: Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium–Diene Complexes in Microemulsions and Conventional Solvents

Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium-Diene Complexes in Microemulsions and Conventional Solvents.

The role of liquid confinement on the asymmetric Rh catalysis was studied using the 1,2-addition of phenylboroxine (2) to N-tosylimine 1 in the presence of [RhCl(C2 H4 )2 ]2 and chiral diene ligands as benchmark reaction. To get access to Rh complexes of different polarity, enantiomerically pure C2 -symmetric p-substituted 3,6-diphenylbicyclo[3.3.0]octadienes 4 and diastereomerically enriched unsymmetric norbornadienes 5 and 6 carrying either the Evans or the SuperQuat auxiliary were synthesized. A microemulsion containing the equal amounts of H2 O/KOH and toluene/reactants was formulated using the hydrophilic sugar surfactant n-octyl β-d-glucopyranoside (C8 G1 ) to mediate the miscibility between the nonpolar reactants and KOH, needed to activate the Rh-diene complex. Prominent features of this organized reaction medium are its temperature insensitivity as well as the presence of water and toluene-rich compartments with a domain size of 55 Å confirmed by small-angle X-ray scattering (SAXS). Although bicyclooctadiene ligands 4 a,b,e performed equally well under homogeneous and microemulsion conditions, ligands 4 c,d gave a different chemoselectivity. For norbornadienes 5, 6, however, microemulsions markedly improved conversion and enantioselectivity as well as reaction rate, as was confirmed by kinetic studies using ligand 5 b.

Computer Simulation of Hydrogen Peroxide Decomposition in a Complex with Dienes and Isopropyl Alcohol

The conformations of molecules in a diene (butadiene, isoprene) complex with hydrogen peroxide and isopropyl alcohol, for which local energy minima are identified, and a mechanism of hydrogen peroxide decomposition have been studied by the quantum-chemical density functional theory method. It has been shown that depending on the initial multiplicity of the system, the decomposition can result in the formation of different intermediate and final products, which indicates the probability of singlet to triplet conversion of hydrogen peroxide in the real system.

Synthesis of and Catalytic Linear Cross-Dimerizations by an Electron-Deficient Cyclic Diene Complex of Ruthenium(0)

A ruthenium(0) complex [Ru(η6-naphthalene)(η4-Ph-dbcot)] (1a: Ph-dbcot = 5-phenyldibenzo[a,e]cyclooctatetraene) is newly prepared in 53% yield. The IR experiment of [Ru(η4-2,3-dimethylbutadiene)(η4-Ph-dbcot)(CO)] (2a) shows this formal zerovalent ruthenium complex to be very electron-deficient, even though the Ph-dbcot ligand does not have any particular electron-withdrawing functional group. Complex 1a shows high catalytic activity toward cross-dimerization between conjugated diene with methyl acrylate with high regioselectivity.

Zwitterionic Rhodium and Iridium Complexes Based on a Carboxylate Bridge-Functionalized Bis-N-heterocyclic Carbene Ligand: Synthesis, Structure, Dynamic Behavior, and Reactivity.

A series of water-soluble zwitterionic complexes featuring a carboxylate bridge-functionalized bis-N-heterocyclic carbene ligand of formula [Cp*MIIICl{(MeIm)2CHCOO}] and [MI(diene){(MeIm)2CHCOO}] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; M = Rh, Ir; MeIm = 3-methylimidazol-2-yliden-1-yl; diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd)) were prepared from the salt [(MeImH)2CHCOO]Br and suitable metal precursor. The solid-state structure of both types of complexes shows a boat-shaped six-membered metallacycle derived of the κ2C,C' coordination mode of the bis-NHC ligand. The uncoordinated carboxylate fragment is found at the bowsprit position in the Cp*MIII complexes, whereas in the MI(diene) complexes it is at the flagpole position of the metallacycle. The complexes [RhI(diene){(MeIm)2CHCOO}] (diene = cod, nbd) exist as two conformational isomers in dichloromethane, bowsprit and flagpole, that interconvert through the boat-to-boat inversion of the metallacycle. An inversion barrier of ∼17 kcal·mol-1 was determined by two-dimensional exchange spectroscopy NMR measurements for [RhI(cod){(MeIm)2CHCOO}]. Reaction of zwitterionic Cp*MIII complexes with methyl triflate or tetrafluoroboric acid affords the cationic complexes [Cp*MIIICl{(MeIm)2CHCOOMe}]+ or [Cp*MIIICl{(MeIm)2CHCOOH}]+ (M = Rh, Ir) featuring carboxy and methoxycarbonyl functionalized methylene-bridged bis-NHC ligands, respectively. Similarly, complexes [MI(diene){(MeIm)2CHCOOMe}]+ (M = Rh, Ir) were prepared by alkylation of the corresponding zwitterionic MI(diene) complexes with methyl triflate. In contrast, reaction of [IrI(cod){(MeIm)2CHCOO}] with HBF4·Et2O (Et = ethyl), CH3OTf, CH3I, or I2 gives cationic iridium(III) octahedral complexes [IrIIIX(cod){(MeIm)2CHCOO}]+ (X = H, Me, or I) featuring a tripodal coordination mode of the carboxylate bridge-functionalized bis-NHC ligand. The switch from κ2C,C' to κ3C,C',O coordination of the bis-NHC ligand accompanying the oxidative addition prevents the coordination of the anions eventually formed in the process that remain as counterions.

Aqueous Asymmetric 1,4-Addition of Arylboronic Acids to Enones Catalyzed by an Amphiphilic Resin-Supported Chiral Diene Rhodium Complex under Batch and Continuous-Flow Conditions

A rhodium-chiral diene complex immobilized on amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin (PS-PEG-diene*-Rh) has been developed. The immobilized rhodium-chiral diene complex (PS-PEG-diene*-Rh) efficiently catalyzed the asymmetric 1,4-addition of various arylboronic acids to cyclic or linear enones in water under batch conditions to give the corresponding β-arylated carbonyl compounds in excellent yields and with excellent enantioselectivity. The catalyst was readily recovered by simple filtration and reused 10 times without loss of its catalytic activity and enantioselectivity. Moreover, a continuous-flow asymmetric 1,4-addition in a flow reactor containing PS-PEG-diene*-Rh proceeded efficiently at 50 °C with retention of high enantioselectivity. Long-term continuous-flow asymmetric 1,4-addition during 12 h readily gave the desired product on a 10 g scale with high enantioselectivity.

Selective [1,4]-Hydrovinylation of 1,3-Dienes with Unactivated Olefins Enabled by Iron Diimine Catalysts.

The selective, intermolecular [1,4]-hydrovinylation of conjugated dienes with unactivated α-olefins catalyzed by α-diimine iron complexes is described. Value-added "skipped" diene products were obtained with exclusive [1,4]-selectivity, and the formation of branched, ( Z)-olefin products was observed with no evidence for alkene isomerization. Mechanistic studies conducted with the well-defined, single-component iron precatalyst (MesDI)Fe(COD) (MesDI = [2,4,6-Me3-C6H2-N═CMe]2); COD = 1,5-cyclooctadiene) provided insights into the origin of the high selectivity. An iron diene complex was identified as the catalyst resting state, and one such isoprene complex, (iPrDI)Fe(η4-C5H8), was isolated and characterized. A combination of single crystal X-ray diffraction, Mößbauer spectroscopy, magnetic measurements, and DFT calculations established that the complex is best described as a high-spin Fe(I) center ( SFe = 3/2) engaged in antiferromagnetic coupling to an α-diimine radical anion ( SDI = -1/2), giving rise to the observed S = 1 ground state. Deuterium-labeling experiments and kinetic analyses of the catalytic reaction provided support for a pathway involving oxidative cyclization of an alkene with the diene complex to generate an iron metallacycle. The observed selectivity can be understood in terms of competing steric interactions in the transition states for oxidative cyclization and subsequent β-hydrogen elimination.

Iridium/Chiral Diene‐Catalyzed Enantioselective (3+2) Annulation of Aromatic Ketimines with 1,3‐Enynes via C−H Activation

AbstractAn iridium/chiral diene complex efficiently catalyzed enantioselective (3+2) annulation between 1,3‐enynes and cyclic N‐acyl ketimines generated in situ from 3‐aryl‐3‐hydroxyisoindoin‐1‐ones. The reaction gave the corresponding aminoindane derivatives in high yields with high regio‐, diastereo‐, and enantioselectivity.magnified image

Synthesis and coordination chemistry of new asymmetric donor/acceptor pincer ligands, 1,3-C6H4(CH2PtBu(Rf))2 (Rf = CF3, C2F5).

Syntheses of new asymmetric pincer precursors 1,3-C6H4{CH2P(tBu,X)}2 (tBu,XPCPH; X = Cl, SiMe3, OPh) and a new class of hybrid donor/acceptor pincer ligands 1,3-C6H4{CH2P(tBu,Rf)}2 (tBu,RfPCPH; Rf = CF3, C2F5) are reported. All tBu,XPCPH compounds are obtained as mixtures of meso and rac diastereomers in varying ratios (meso : rac ∼ 4 : 1 to 3 : 2) which were used without separation. Treatment of Ru(cot)(cod) with tBu,CF3PCPH under 1 atm H2 in acetone at 20 °C produced the hydride solvate (tBu,CF3PCP)Ru(acetone)xH which was not isolated, but could be trapped as stable diene complexes (tBu,CF3PCP)Ru(L)2H (L2 = cod (1[combining low line]), nbd (2[combining low line])). Catalytic cyclooctane dehydrogenation studies demonstrate that 2[combining low line] has ∼50% the activity of (CF3PCP)Ru(cod)(H), but significantly higher catalyst stability and is able to operate at higher catalyst loading concentrations without deactivation via bimolecular decomposition.

A Rapid Synthesis of Chiral Allylic Amines via Microwave‐assisted Asymmetric Alkenylation of N‐Tosyl Aldimines Catalyzed by Rhodium/Chiral Diene Complexes

A method providing expeditious access to chiral allylic amines via a Rh(I)/bicyclo[2.2.1]heptadiene‐catalyzed enantioselective alkenylation of N‐tosyl aldimines with potassium alkenyltrifluoroborates under microwave irradiation is described. The rate of the asymmetric 1,2‐addition reaction, conducted in the presence of 1 mol % of the catalyst, was significantly enhanced as compared to when the standard heating method was applied while still providing the corresponding products without decrease in enantioselectivity.

Organoboron Initiated Rh-Catalyzed Asymmetric Cascade Reactions: A Subtle Switch in Regioselectivity Leading to Chiral 3-Benzazepine Derivatives

An addition-carbocyclization cascade reaction initiated by arylboronic acids and catalyzed by a rhodium/chiral diene complex is described. Starting from N-bridged yne-enoate derivatives, chiral functionalized seven-membered 3-benzazepine heterocycles were obtained with high enantioselectivities, thanks to a rhodium 1,4-shift.

イリジウム触媒による高原子効率型の不斉合成反応

This article summarizes our recent studies on iridium-catalyzed asymmetric reactions realizing the high atom efficiency. Iridium complexes efficiently catalyzed asymmetric functionalization of aromatic compounds via directed C-H activation. Formal [3+2] annulation of ketimines with 1,3-dienes or alkynes gave the corresponding annulation products in high yields with high enantioselectivity. Branch-selective alkylation of aromatic compounds with vinyl ethers was efficiently catalyzed by Ir(I)/chiral diene complexes. Hydroacylation of bicyclic alkenes with salicylaldehydes also proceeded via acyl C-H bond activation. Meanwhile, asymmetric synthesis of heterocycles via C-O and C-N bond formation were also achieved. Annulation of salicylimines and α-oxocarboxamides with 1,3-dienes proceeded to give chromane and pyrrolidone derivatives, respectively. Asymmetric cyclization of alkenoic acids and alkenamides took place to give γ-lactones and γ-lactams, respectively.

A DFT calculation-inspired Rh(i)-catalyzed reaction via suppression of α-H shift in α-alkyldiazoacetates.

Metal-associated carbenes from diazo compounds promote many useful chemistry transformations in modern organic chemistry. However, compared to α-aryldiazoacetate-derived carbenes (ArDCs), the synthetic application of α-alkyldiazoacetate-derived carbenes (AlDCs) is greatly limited due to intramolecular α-H transfer (elimination) that results in alkenes as the main by-products. An intriguing α-alkyldiazoacetate-involved three-component reaction has been developed following DFT calculation inspiration to provide β-hydroxyl α-alkyl-α-amino acid derivatives in good yields. The intramolecular α-H shift of an α-alkyldiazoacetate-derived carbene was successfully suppressed by the association of a Rh(i) complex to form the corresponding active ammonium ylide, which was trapped before the fast 1,2-H transfer process. A Rh(i)-chiral diene complex was identified as an effective catalyst to give an asymmetric version of the reaction with good enantioselectivity. This reaction provides insight into extending the efficient transformation of α-alkyldiazoacetate-derived carbenes and their synthetic application.

Asymmetric Transformations under Iridium/Chiral Diene Catalysis

Chelating chiral dienes have become steering ligands for iridium in several types of asymmetric reactions. Some effective examples realized only by use of chiral diene ligands instead of conventional ligands based on phosphine and nitrogen have appeared in the iridium-catalyzed processes. In particular, it should be noted that Ir/chiral diene catalysts allow enantioselective reactions involving C–H bond activation. In this Perspective, recent progress in asymmetric reactions catalyzed by Ir/chiral diene complexes is summarized.

Asymmetric Cyclization of N-Sulfonyl Alkenyl Amides Catalyzed by Iridium/Chiral Diene Complexes.

Iridium/chiral diene complexes efficiently catalyzed the asymmetric cyclization of N-sulfonyl alkenyl amides to give the corresponding 2-pyrrolidone derivatives with high enantioselectivity. A mechanistic study revealed that the reaction proceeds via nucleophilic attack of the amide on the alkene moiety.

ChemInform Abstract: Asymmetric Alkylation of N‐Sulfonylbenzamides with Vinyl Ethers via C—H Bond Activation Catalyzed by Hydroxoiridium/Chiral Diene Complexes.

AbstractThis method uses an iridium diene catalyst for the alkylation of benzamides with vinyl ethers giving the branched products in good yields and with excellent enantioselectivities.