Photoredox Oxidation of Alkanes by Monometallic Copper-Oxygen Complexes Using Visible Light Including One Sun Illumination.

Oxygenation of hydrocarbons offers versatile catalytic routes to more valuable compounds, such as alcohols, aldehydes, and ketones. Despite the importance of monometallic copper-oxygen species as hydroxylating agents in biology, few synthetic model compounds are known to react with hydrocarbons, owing to high C-H bond dissociation energies. To overcome this challenge, the photoredox chemistry of monometallic copper (pyrazolyl)borate complexes coordinated by chlorate has been explored in the presence of C-C alkanes with BDEs ≥ 93 kcal/mol.

Phenoxythiazoline (FTz)-Cobalt(II) Precatalysts Enable C(sp )-C(sp ) Bond-Formation for Key Intermediates in the Synthesis of Toll-like Receptor 7/8 Antagonists.

Evaluation of the relative rates of the cobalt-catalyzed C(sp )-C(sp ) Suzuki-Miyaura cross-coupling between the neopentylglycol ester of 4-fluorophenylboronic acid and N-Boc-4-bromopiperidine established that smaller N-alkyl substituents on the phenoxyimine (FI) supporting ligand accelerated the overall rate of the reaction. This trend inspired the design of optimal cobalt catalysts with phenoxyoxazoline (FOx) and phenoxythiazoline (FTz) ligands. An air-stable cobalt(II) precatalyst, (FTz)CoBr(py) was synthesized and applied to the cross-coupling of an indole-5-boronic ester nucleophile with a piperidine-4-bromide electrophile that is relevant to the synthesis of reported toll-like receptor (TLR) 7/8 antagonist molecules including afimetoran.

Mechanistic Investigations of Phenoxyimine-Cobalt(II)-Catalyzed C(sp)-C(sp) Suzuki-Miyaura Cross-Coupling.

The mechanism of phenoxyimine (FI)-cobalt-catalyzed C(sp)-C(sp) Suzuki-Miyaura cross-coupling was studied using a combination of kinetic measurements and catalytic and stoichiometric experiments. A series of dimeric (FI)cobalt(II) bromide complexes, [(4-CFPhFI)CoBr], [(4-OMePhFI)CoBr], and [(2,6-diPrPhFI)CoBr], were isolated and characterized by H and F NMR spectroscopies, solution and solid-state magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray crystallography, and diffusion-ordered NMR spectroscopy (DOSY). One complex, [(4-CFPhFI)CoBr], was explored as a single-component precatalyst for C(sp)-C(sp) Suzuki-Miyaura cross-coupling.

Cobalt-Catalyzed C(sp)-C(sp) Suzuki-Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands.

Cobalt(II) halides in combination with phenoxy-imine (FI) ligands generated efficient precatalysts for the C(sp)-C(sp) Suzuki-Miyaura cross coupling between alkyl bromides and neopentylglycol (hetero)arylboronic esters. The protocol enabled efficient C-C bond formation with a host of nucleophiles and electrophiles (36 examples, 34-95%) with precatalyst loadings of 5 mol%. Studies with alkyl halide electrophiles that function as radical clocks support the intermediacy of alkyl radicals during the course of the catalytic reaction.

Taming the Chlorine Radical: Enforcing Steric Control over Chlorine-Radical-Mediated C-H Activation.

Chlorine radicals readily activate C-H bonds, but the high reactivity of these intermediates precludes their use in regioselective C-H functionalization reactions. We demonstrate that the secondary coordination sphere of a metal complex can confine photoeliminated chlorine radicals and afford steric control over their reactivity. Specifically, a series of iron(III) chloride pyridinediimine complexes exhibit activity for photochemical C(sp)-H chlorination and bromination with selectivity for primary and secondary C-H bonds, overriding thermodynamic preference for weaker tertiary C-H bonds.

Capturing the Complete Reaction Profile of a C-H Bond Activation.

The activation of C-H bonds requires the generation of extremely reactive species, which hinders the study of this reaction and its key intermediates. To overcome this challenge, we synthesized an iron(III) chloride-pyridinediimine complex that generates a chlorine radical proximate to reactive C-H bonds upon irradiation with light. Transient spectroscopy confirms the formation of a Cl·|arene complex, which then activates C-H bonds on the PDI ligand to yield HCl and a carbon-centered radical as determined by photocrystallography.

Oxygen activation at a dicobalt centre of a dipyridylethane naphthyridine complex.

The mechanism of oxygen activation at a dicobalt bis-μ-hydroxo core is probed by the implementation of synthetic methods to isolate reaction intermediates. Reduction of a dicobalt(iii,iii) core ligated by the polypyridyl ligand dipyridylethane naphthyridine (DPEN) by two electrons and subsequent protonation result in the release of one water moiety to furnish a dicobalt(ii,ii) center with an open binding site. This reduced core may be independently isolated by chemical reduction.

Structurally characterized terminal manganese(iv) oxo tris(alkoxide) complex.

A Mn(iv) complex featuring a terminal oxo ligand, [Mn(O)(ditox)][K(15-C-5)] (; ditox = BuMeCO, 15-C-5 = 15-crown-5-ether) has been isolated and structurally characterized. Treatment of the colorless precursor [Mn(ditox)][K(15-C-5)] () with iodosobenzene affords as a green free-flowing powder in high yields. The X-ray crystal structure of reveals a pseudotetrahedral geometry about the central Mn, which features a terminal oxo ((Mn-O = 1.

Overcoming double-step CO adsorption and minimizing water co-adsorption in bulky diamine-appended variants of Mg(dobpdc).

Alkyldiamine-functionalized variants of the metal-organic framework Mg(dobpdc) (dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO capture applications owing to their unique step-shaped CO adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. , (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO adsorption/desorption profiles.

Cooperative insertion of CO2 in diamine-appended metal-organic frameworks.

The process of carbon capture and sequestration has been proposed as a method of mitigating the build-up of greenhouse gases in the atmosphere. If implemented, the cost of electricity generated by a fossil fuel-burning power plant would rise substantially, owing to the expense of removing CO2 from the effluent stream. There is therefore an urgent need for more efficient gas separation technologies, such as those potentially offered by advanced solid adsorbents.