Supercritical Carbon Dioxide as a Reaction Medium for Silane-Mediated Free-Radical Carbonylation of Alkyl Halides

Supercritical Carbon Dioxide as a Reaction Medium for Silane-Mediated Free-Radical Carbonylation of Alkyl Halide

Reaction of 16-Electron Ruthenium and Iridium Amide Complexes with Acidic Alcohols: Intramolecular C−H Bond Activation and the Isolation of Cyclometalated Complexes

The 16-electron transition metal amide complexes, Cp*M[κ2(N,N‘)-(S,S)-TsNCHPhCHPhNH] (M = Ir, Rh, Cp* = pentamethylcyclopentadienyl, Ts = p-toluenesulfonyl, Ph = C6H5) and Ru[κ2(N,N‘)-(S,S)-TsNCHPhCHPhNH](p-cymene), react with acidic alcohols, CF3CH2OH or phenols, to give the corresponding alkoxide complexes, which are readily convertible to metallacycles via intramolecular C−H bond activation of the aromatic group on the diamine ligand. For example, the Ir and Rh amide complexes are transformed to the metallacycles Cp*M[κ3(N,N‘,C)-(S,S)-CH3C6H3SO2NCHPhCHPhNH2] (M = Ir, Rh), while the Ru amide complex having structures isoelectronic with the Cp*Ir complex gives two types of metallacycles, Ru[κ3(N,N‘,C)-(S,S)-CH3C6H3SO2NCHPhCHPhNH2](p-cymene) and Ru[κ3(N,N‘,C)-(S,S)-TsNCHPhCH(C6H4)NH2](p-cymene), which are formed by the C−H bond activation of an aromatic ring in either the Ts group or the diamine ligand. NMR study for the cyclometalation of the Ir amide complex with phenols suggests that the reaction proceeds through the phenoxide complexes as intermediates

Quantum Chemical Calculations with the Inclusion of Nonspecific and Specific Solvation: Asymmetric Transfer Hydrogenation with Bifunctional Ruthenium Catalysts

Details of the mechanism of asymmetric transfer hydrogenation of ketones catalyzed by two chiral bifunctional ruthenium complexes, (<i>S</i>)-RuH­[(<i>R,R</i>)-OCH­(Ph)­CH­(Ph)­NH₂]­(η⁶-benzene) (<b>Ru-1</b>) or (<i>S</i>)-RuH­[(<i>R,R</i>)-<i>p</i>-TsNCH­(Ph)­CH­(Ph)­NH₂]­(η⁶-mesityl­ene) (<b>Ru-2</b>), were studied computationally by density functional theory, accounting for the solvation effects by using continuum, discrete, and mixed continuum/discrete solvation models via “solvated supermolecules” approach. In contrast to gas phase quantum chemical calculations, where the reactions were found to proceed via a concerted three-bond asynchronous process through a six-membered pericyclic transition state, incorporation of the implicit and/or explicit solvation into the calculations suggests that the same reactions proceed via two steps in solution: (i) enantio-determining hydride transfer and (ii) proton transfer through the contact ion-pair intermediate, stabilized primarily by ionic hydrogen bonding between the cation and the anion. The calculations suggest that the proton source for neutralizing the chiral RO^– anion may be either the amine group of the cationic Ru complex or, more likely, a protic solvent molecule. In the latter case, the reaction may not necessarily proceed via the 16e amido complex Ru­[(<i>R,R</i>)-XCH­(Ph)­CH­(Ph)­NH]­(η⁶-arene). The origin of enantioselectivity is discussed in terms of the newly formulated mechanism

Enantioselective Michael Reaction Catalyzed by Well-Defined Chiral Ru Amido Complexes: Isolation and Characterization of the Catalyst Intermediate, Ru Malonato Complex Having a Metal−Carbon Bond

Chiral Ru amido complexes promote asymmetric Michael addition of malonates to cyclic enones, leading to Michael adducts with excellent ee's, in which the chiral Ru amido complexes react with malonates to give isolable catalyst intermediates, chiral Ru malonato complexes bearing a metal bound C-nucleophile

A Sulfonylimido-Bridged Coordinatively Unsaturated Diiridium Complex: Intramolecular C−H Bond Activation Promoted by a Weak Acid

The sulfonylimido-bridged diiridium complex [Cp*Ir(μ2-NTs)2IrCp*] (1; Cp* = η5-C5(CH3)5, Ts = SO2C6H4CH3-p), readily accessible from the reaction of [Cp*IrCl2]2 with TsNH2, reacted with P(CH3)3 and HOTf (Tf = SO2CF3) to afford the adduct [Cp*Ir{P(CH3)3}(μ2-NTs)2IrCp*] and cationic amido−imido complex [Cp*Ir(μ2-NHTs)(μ2-NTs)IrCp*][OTf], respectively. On the other hand, the reaction of 1 with benzoic acid resulted in intramolecular C−H bond activation, giving the cyclometalated complex [Cp*Ir{μ2-NHSO2C6H3(CH3)-κ2N,C}2IrCp*]

Halide-Free Dehydrative Allylation Using Allylic Alcohols Promoted by a Palladium−Triphenyl Phosphite Catalyst

The triphenyl phosphite−palladium complex was found to effect catalytic substitution reactions of allylic alcohols via a direct C−O bond cleavage. The dehydrative etherification proceeded efficiently without any cocatalysts and bases to give allylic ethers in good to excellent yields

Well-Defined Triflylamide-Tethered Arene−Ru(Tsdpen) Complexes for Catalytic Asymmetric Hydrogenation of Ketones

Well-defined triflylamide-tethered arene−Ru(Tsdpen) complexes have been developed as highly efficient catalysts for the asymmetric hydrogenation of ketones, in which the suitable carbon chain length of the tether is responsible for the activation of H2 as well as the stereochemical outcome of the reaction. The asymmetric hydrogenation of aromatic ketones with the tethered complex with a C4 side chain gave the corresponding secondary alcohols with 91−98% ee, while the shorter congeners with a C2 or C3 side chain provided unsatisfactory results in terms of reactivity and selectivity

Stereoselective Formation of α-Alkylidene Cyclic Carbonates via Carboxylative Cyclization of Propargyl Alcohols in Supercritical Carbon Dioxide

Carboxylative cyclization of propargyl alcohols in supercritical carbon dioxide (scCO2) containing P(n-C4H9)3 as a catalyst proceeded smoothly to give α-alkylidene-1,3-dioxolan-2-ones. Internal propargyl alcohols afforded Z-alkyl-idene cyclic carbonates exclusively. CO2 incorporation was markedly promoted under supercritical conditions, possibly due to the facile formation of a putative P(n-C4H9)3−CO2 adduct as a key intermediate

Hydrogen- and Oxygen-Driven Interconversion between Imido-Bridged Dirhodium(III) and Amido-Bridged Dirhodium(II) Complexes

The reaction of [Cp*RhCl2]2 (Cp* = η5-C5(CH3)5) with 2 equiv of p-toluenesulfonamide in the presence of KOH resulted in the formation of the sulfonylimido-bridged dirhodium(III) complex [(Cp*Rh)2(μ-NTs)2] (1a; Ts = SO2C6H4CH3-p). The imido complex 1a reacted with hydrogen donors such as H2 and 2-propanol to give the sulfonylamido-bridged dirhodium(II) complex [(Cp*Rh)2(μ-NHTs)2] (2). Treatment of the (amido)rhodium(II) complex 2 with O2 regenerated the (imido)rhodium(III) complex 1a. Complex 1a also underwent reversible protonation to afford the cationic amido- and imido-bridged dirhodium(III) complex [(Cp*Rh)2(μ-NHTs)(μ-NTs)]+ (4), which further reacted with H2 or 2-propanol to give the (hydrido)bis(amido)dirhodium(III) complex [(Cp*Rh)2(μ-H)(μ-NHTs)2]+ (5). On the basis of DFT calculations and experimental results using 4 and 5, the reaction of 1a with H2 proved to proceed via heterolytic cleavage of H2 assisted by the sulfonyl oxygen atom followed by proton migration from the metal center. Furthermore, the redox interconversion between 1a and 2 was applied to catalytic aerobic oxidation of H2 and an alcohol by using 1a as a well-defined dinuclear catalyst. The iridium complex [(Cp*Ir)2(μ-NTs)2] (1b) as well as a rhodium complex [Cp*RhCl2]2 without bridging imido ligands did not catalyze these aerobic oxidation reactions

Isolation and Interconversion of Protic<i></i> N-Heterocyclic Carbene and Imidazolyl Complexes: Application to Catalytic Dehydrative Condensation of <i>N</i>-(2-Pyridyl)benzimidazole and Allyl Alcohol

Treatment of the protic N-heterocyclic carbene (NHC) complex [Cp*RuCl(LH)] (2; LH = N-(2-pyridyl)benzimidazolin-2-ylidene-κ2N,C) with AgNO2 gives the nitrosyl–imidazolyl complex [Cp*Ru(NO)(L)][OTf] (OTf = OSO2CF3), which undergoes reversible protonation to afford the NHC complex [Cp*Ru(NO)(LH)][OTf]2. The bifunctional complex 2 also catalyzes the dehydrative condensation of N-(2-pyridyl)benzimidazole and allyl alcohol, leading to the formation of trans- and cis-2-(1-propenyl)-N-(2-pyridyl)benzimidazole