Antiaromatic compounds have recently received considerable attention because of their novel properties such as narrow HOMO-LUMO gaps and facile formation of mutual stacking. Here, the spontaneous assembly of antiaromatic meso-2-thienyl-substituted 5,15-dioxaporphyrin (DOP-1) is scrutinized at the liquid-solid interface by scanning tunneling microscopy (STM). Polymorphism in monolayers characterized by the orthogonal and parallel assemblies is found at the low concentration of 0.05 mM. The parallel assembly is more stable and dominantly formed at higher concentrations. Aggregation was observed at concentrations > 0.2 mM, and the STM images of the aggregates implied the formation of stacked layers. The intrinsic electronic structures of the mutually stacked bilayer generated by applying an electric pulse to the monolayer were probed by scanning tunneling spectroscopy to reveal the narrowing of the HOMO-LUMO gap by about 20 % compared with the monolayer, thus suggesting significant molecular orbital interactions.
Visible light-driven cross-coupling reactions of alkyl halides with phenylacetylene and its derivatives catalyzed by the cobalamin derivative (B12) with the [Ir(dtbbpy)(ppy)2]PF6 photocatalyst at room temperature are reported.
A series of Ir complexes has been developed as multifunctional photocatalysts for CO2 reduction to give HCO2H selectively. The catalytic activities and photophysical properties vary widely across the series, and...
Although
hydrocarbons are known to act as reductants for the catalytic
reduction of nitric oxides (NO
x
) over
copper-based catalysts, the reaction mechanism requires clarification.
Herein, density functional theory (DFT) calculations were carried
out to investigate the reduction mechanisms of NO
x
to dinitrogen coupled to the hydroxylation of methane or
benzene using the dicopper complex reported by Zhang and co-workers
[J. Am. Chem. Soc.20191411015910164]. The B3LYP functional was used to optimize
the (μ-oxo)(μ-nitrosyl)dicopper complex in the quartet
state and the (μ-η2:η2-NO2)dicopper complex in the doublet state, the latter of which
was found to be the ground state. Then, we investigated the reactivities
of the (μ-η2:η2-NO2)dicopper complex toward methane and benzene by considering the conversions
of N2O to N2 in the presence and the absence
of methane or benzene. In the presence of methane and benzene, the
calculated activation energies were 27.0 and 21.0 kcal/mol, respectively,
whereas that with N2O alone was prohibitively high (61.9
kcal/mol). Thus, the (μ-η2:η2-NO2)dicopper complex prefers the reactions with methane
and benzene to that with N2O. The reaction of the (μ-η2:η2-NO2)dicopper complex with
methane or benzene generated the (μ-nitrosyl)dicopper complex.
The (μ-nitrosyl)dicopper complex then reacted with N2O to regenerate the (μ-η2:η2-NO2)dicopper complex and N2 with an activation
barrier of 31.5 kcal/mol. The overall reactions for methane and benzene
hydroxylation were calculated to be exothermic by 41.7 and 54.1 kcal/mol,
respectively. These results suggest that the catalytic reduction of
NO
x
using hydrocarbons is feasible at
certain operating temperatures. Thus, our calculations provide new
insights into the design of catalysts for NO
x
purification.
A density functional theory study was carried out to investigate the reduction mechanisms of NO to N2O using a dicopper complex reported by Zhang and coworkers (J. Am. Chem. Soc....
Antiaromatic compounds have recently received considerable attention because of their novel properties such as narrow HOMO–LUMO gaps and facile formation of mutual stacking. Here, the spontaneous assembly of antiaromatic meso‐2‐thienyl‐substituted 5,15‐dioxaporphyrin (DOP‐1) is scrutinized at the liquid‐solid interface by scanning tunneling microscopy (STM). Polymorphism in monolayers characterized by the orthogonal and parallel assemblies is found at the low concentration of 0.05 mM. The parallel assembly is more stable and dominantly formed at higher concentrations. Aggregation was observed at concentrations >0.2 mM, and the STM images of the aggregates implied the formation of stacked layers. The intrinsic electronic structures of the mutually stacked bilayer generated by applying an electric pulse to the monolayer were probed by scanning tunneling spectroscopy to reveal the narrowing of the HOMO–LUMO gap by about 20 % compared with the monolayer, thus suggesting significant molecular orbital interactions.
Co(II)-pyrocobester (P -Co(II) ), a dehydrocorrin complex, was semisynthesized from vitamin B 12 (cyanocobalamin), and its photochemical and electrochemical properties were investigated and compared to those of the cobester (C -Co(II) ), the cobalt-corrin complex. The UV−vis absorptions of P -Co(II) in CH 2 Cl 2 , ascribed to the π−π* transition, were red-shifted compared to those of C -Co(II) due to the πexpansion of the macrocycle in the pyrocobester. The reversible redox couple of P -Co(II) was observed at E 1/2 = −0.30 V vs Ag/AgCl in CH 3 CN, which was assigned to the Co(II)/Co(I) redox couple by UV−vis, ESR, and molecular orbital analysis. This redox couple was positively shifted by 0.28 V compared to that of C -Co(II) . This is caused by the high electronegativity of the dehydrocorrin macrocycle, which was estimated by DFT calculations for the free-base ligands. The reactivity of the Co(I)pyrocobester (P -Co(I) ) was evaluated by the reaction with methyl iodide in CV and UV−vis to form a photosensitive Co(III)-CH 3 complex (P -Co(III)-CH3 ). The properties of the excited state of P -Co(I) , *Co(I), were also investigated by femtosecond transient absorption (TA) spectroscopy. The lifetime of *Co(I) was estimated to be 29 ps from the kinetic trace at 587 nm. The lifetime of *Co(I) became shorter in the presence of Ar-X, such as iodobenzonitrile (1a), bromobenzonitrile (1b), and chlorobenzonitrile (1c), and the rate constants of electron transfer (ET) between the *Co(I) and Ar-X were determined to be 2.
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