C–H Functionalization Reactivity of a Nickel–Imide

This article discusses C-H functionalization reactivity of a Nickel-Imide

Oxyfunctionalization with Cp*Ir^III(NHC)(Me)(Cl) with O₂: Identification of a Rare Bimetallic Ir^IV μ‑Oxo Intermediate

Methanol formation from [Cp*Ir^III(NHC)­Me­(CD₂Cl₂)]⁺ occurs quantitatively at room temperature with air (O₂) as the oxidant and ethanol as a proton source. A rare example of a diiridium bimetallic complex, [(Cp*Ir­(NHC)­Me)₂(μ-O)]­[(BAr^F₄)₂], <b>3</b>, was isolated and shown to be an intermediate in this reaction. The electronic absorption spectrum of <b>3</b> features a broad observation at ∼660 nm, which is primarily responsible for its blue color. In addition, <b>3</b> is diamagnetic and can be characterized by NMR spectroscopy. Complex <b>3</b> was also characterized by X-ray crystallography and contains an Ir^IV–O–Ir^IV core in which two d⁵ Ir­(IV) centers are bridged by an oxo ligand. DFT and MCSCF calculations reveal several important features of the electronic structure of <b>3</b>, most notably, that the μ-oxo bridge facilitates communication between the two Ir centers, and σ/π mixing yields a nonlinear arrangement of the μ-oxo core (Ir–O–Ir ∼ 150°) to facilitate oxygen atom transfer. The formation of <b>3</b> results from an Ir oxo/oxyl intermediate that may be described by two competing bonding models, which are close in energy and have formal Ir–O bond orders of 2 but differ markedly in their electronic structures. The radical traps TEMPO and 1,4-cyclohexadiene do not inhibit the formation of <b>3</b>; however, methanol formation from <b>3</b> is inhibited by TEMPO. Isotope labeling studies confirmed the origin of the methyl group in the methanol product is the iridium–methyl bond in the [Cp*Ir­(NHC)­Me­(CD₂Cl₂)]­[BAr^F₄] starting material. Isolation of the diiridium-containing product [(Cp*Ir­(NHC)­Cl)₂]­[(BAr^F₄)₂], <b>4</b>, in high yields at the end of the reaction suggests that the Cp* and NHC ligands remain bound to the iridium and are not significantly degraded under reaction conditions

Reductive functionalization of a rhodium(iii)–methyl bond by electronic modification of the supporting ligand

Net reductive elimination (RE) of MeX (X = halide or pseudo-halide: Cl(-), CF3CO2(-), HSO4(-), OH(-)) is an important step during Pt-catalyzed hydrocarbon functionalization. Developing Rh(I/III)-based catalysts for alkane functionalization is an attractive alternative to Pt-based systems, but very few examples of RE of alkyl halides and/or pseudo-halides from Rh(III) complexes have been reported. Here, we compare the influence of the ligand donor strength on the thermodynamic potentials for oxidative addition and reductive functionalization using [(t)Bu3terpy]RhCl (1) {(t)Bu3terpy = 4,4',4''-tri-tert-butylpyridine} and [(NO2)3terpy]RhCl (2) {(NO2)3terpy = 4,4',4''-trinitroterpyridine}. Complex 1 oxidatively adds MeX {X = I(-), Cl(-), CF3CO2(-) (TFA(-))} to afford [(t)Bu3terpy]RhMe(Cl)(X) {X = I(-) (3), Cl(-) (4), TFA(-) (5)}. By having three electron-withdrawing NO2 groups, complex 2 does not react with MeCl or MeTFA, but reacts with MeI to yield [(NO2)3terpy]RhMe(Cl)(I) (6). Heating 6 expels MeCl along with a small quantity of MeI. Repeating this experiment but with excess [Bu4N]Cl exclusively yields MeCl, while adding [Bu4N]TFA yields a mixture of MeTFA and MeCl. In contrast, 3 does not reductively eliminate MeX under similar conditions. DFT calculations successfully predict the reaction outcome by complexes 1 and 2. Calorimetric measurements of [(t)Bu3terpy]RhI (7) and [(t)Bu3terpy]RhMe(I)2 (8) were used to corroborate computational models. Finally, the mechanism of MeCl RE from 6 was investigated via DFT calculations, which supports a nucleophilic attack by either I(-) or Cl(-) on the Rh-CH3 bond of a five-coordinate Rh complex

Methane Oxidation to Methanol Catalyzed by Cu-Oxo Clusters Stabilized in NU-1000 Metal–Organic Framework

Copper oxide clusters synthesized via atomic layer deposition on the nodes of the metal–organic framework (MOF) NU-1000 are active for oxidation of methane to methanol under mild reaction conditions. Analysis of chemical reactivity, in situ X-ray absorption spectroscopy, and density functional theory calculations are used to determine structure/activity relations in the Cu-NU-1000 catalytic system. The Cu-loaded MOF contained Cu-oxo clusters of a few Cu atoms. The Cu was present under ambient conditions as a mixture of ∼15% Cu⁺ and ∼85% Cu²⁺. The oxidation of methane on Cu-NU-1000 was accompanied by the reduction of 9% of the Cu in the catalyst from Cu²⁺ to Cu⁺. The products, methanol, dimethyl ether, and CO₂, were desorbed with the passage of 10% water/He at 135 °C, giving a carbon selectivity for methane to methanol of 45–60%. Cu oxo clusters stabilized in NU-1000 provide an active, first generation MOF-based, selective methane oxidation catalyst

Installing Heterobimetallic Cobalt–Aluminum Single Sites on a Metal Organic Framework Support

A heterobimetallic cobalt–aluminum complex was immobilized onto the metal organic framework NU-1000 using a simple solution-based deposition procedure. Characterization data are consistent with a maximum loading of a single Co–Al complex per Zr₆ node of NU-1000. Furthermore, the data support that the Co–Al bimetallic complex is evenly distributed throughout the NU-1000 particle, binds covalently to the Zr₆ nodes, and occupies the NU-1000 apertures with the shortest internode distances (∼8.5 Å). Heating the anchored Co–Al complex on NU-1000 at 300 °C for 1 h in air completely removes the organic ligand of the complex without affecting the structural integrity of the MOF support. We propose that a Co–Al oxide cluster is formed in place of the anchored complex in NU-1000 during heating. Collectively, the results suggest that well-defined heterobimetallic complexes can be effective precursors for installing two different metals simultaneously onto a MOF support. The CoAl-functionalized NU-1000 samples catalyze the oxidation of benzyl alcohol to benzaldehyde with <i>tert</i>-butyl hydroperoxide as a stoichiometric oxidant. Density functional theory calculations were performed to elucidate the detailed structures of the Co–Al active sites on the Zr₆-nodes, and a Co-mediated catalytic mechanism is proposed