Mechanism of efficient anti-Markovnikov olefin hydroarylation catalyzed by homogeneous Ir(III) complexes

The mechanism of the hydroarylation reaction between unactivated olefins (ethylene, propylene, and styrene) and benzene catalyzed by [(R)Ir(μ-acac-O,O,C^3)-(acac-O,O)_2]_2 and [R-Ir(acac-O,O)_2(L)] (R = acetylacetonato, CH_3, CH_2CH_3, Ph, or CH_2CH_2Ph, and L = H_2O or pyridine) Ir(III) complexes was studied by experimental methods. The system is selective for generating the anti-Markovnikov product of linear alkylarenes (61 : 39 for benzene + propylene and 98 : 2 for benzene + styrene). The reaction mechanism was found to follow a rate law with first-order dependence on benzene and catalyst, but a non-linear dependence on olefin. ^(13)C-labelling studies with CH_3^(13)CH_2-Ir-Py showed that reversible β-hydride elimination is facile, but unproductive, giving exclusively saturated alkylarene products. The migration of the ^(13)C-label from the α to β-positions was found to be slower than the C–H activation of benzene (and thus formation of ethane and Ph-d_5-Ir-Py). Kinetic analysis under steady state conditions gave a ratio of the rate constants for CH activation and β-hydride elimination (k_(CH): k_β) of 0.5. The comparable magnitude of these rates suggests a common rate determining transition state/intermediate, which has been shown previously with B3LYP density functional theory (DFT) calculations. Overall, the mechanism of hydroarylation proceeds through a series of pre-equilibrium dissociative steps involving rupture of the dinuclear species or the loss of L from Ph-Ir-L to the solvento, 16-electron species, Ph-Ir(acac-O,O)_2-Sol (where Sol refers to coordinated solvent). This species then undergoes trans to cis isomerization of the acetylacetonato ligand to yield the pseudo octahedral species cis-Ph-Ir-Sol, which is followed by olefin insertion (the regioselective and rate determining step), and then activation of the C–H bond of an incoming benzene to generate the product and regenerate the catalyst

Facile Functionalization of a Metal Carbon Bond by O-Atom Transfer

The facile conversion of M−R to M−OR that could be useful for the functionalization of electron-rich metal alkyl intermediates is shown to proceed via a Baeyer−Villiger-type pathway involving a nonredox, electrophilic, O-atom insertion in reactions with non-peroxo O-donors

Facile oxy-functionalization of a nucleophilic metal alkyl with a cis-dioxo metal species via a (2+3) transition state

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<i>N</i>‑Difluoromethylation of Imidazoles and Benzimidazoles Using the Ruppert–Prakash Reagent under Neutral Conditions

Direct <i>N</i>-difluoromethylation of imidazoles and benzimidazoles has been achieved using TMS-CF₃ (the Ruppert–Prakash reagent) under neutral conditions. Difluoromethylated products were obtained in good-to-excellent yields. Inexpensive, commercially available starting materials, neutral conditions, and shorter reaction times are advantages of this methodology. Reactions are accessible through conventional as well as microwave irradiation conditions

Design and study of homogeneous catalysts for the selective, low temperature oxidation of hydrocarbons

The direct, low temperature conversion of hydrocarbons to functionalized products using novel, single site catalysts could lead to technological advances that redefine the landscape of the current materials and energy industries. Natural gas continues to represent a vast source of untapped hydrocarbons around the globe that has the potential to replace or augment petroleum as the raw material for materials and energy. Its abundance has garnered much interest in the scientific community as groups have focused on the catalytic conversion of its major component, methane, to functionalized products. The key requirements is to design new catalysts for the oxidative functionalization of methane that operate at lower temperatures and that also meet the basic requirements of selectivity, rate, and lifetime that characterize useful catalysts. Recent advances in the field of hydrocarbon CH activation have shown the potential for transition metal based coordination catalysts to meet these requirements. Described herein are recent advances in designing catalysts based on the CH activation reaction that address the basic requirements for practical systems with emphasis on the issues that have prevented promising reported systems from becoming commercially viable