Search

The Cu−O−Cu core exhibits methane‐to‐methanol conversion, mirroring the reactivity of the copper–containing enzyme pMMO. Herein, we computationally examined the reactivity of a biomimetic Cu−O−Cu core towards methane–to–methanol conversion. The oxygen atom of the Cu−O−Cu core abstracts hydrogen present in the C−H bond of methane. The spin density at the bridging oxygen helps to abstract hydrogen from the C−H bond. We modulated the spin density of the bridging oxygen by substituting only a single copper atom of the Cu−O−Cu core by metals (M) such as Fe, Co, and Ag. These substitutions result in bimetallic [Cu−O−M]2+ models. We observed that the energy barriers for the C−H activation step and the subsequent rebound step vary with the metal M. [Cu−O−Ag]2+ exhibits the highest reactivity for M2M conversion, while [Cu−O−Fe]2+ displays the lowest reactivity. To understand the different reactivity of these models towards M2M conversion, we employed distortion‐interaction analysis, orbital analysis, spin density analysis, and quantum theory of atoms in molecules analysis. Orbital analysis reveals that all four adducts follow a hydrogen atom transfer mechanism for C−H activation. Further, spin density analysis reveals that a higher spin density on the bridging oxygen leads to a lower C−H activation barrier. [ABSTRACT FROM AUTHOR]

A class of 2‐hydroxypyridine based ligands are explored to achieve enhanced catalytic activity for ortho‐C−H bond activation/arylation reaction over [(η6‐p‐cymene)RuCl2]2 catalyst in water. Extensive studies using a series of substituted 2‐hydroxypyridine based ligands (L1–L6) inferred that 5‐trifluoromethyl‐2‐hydroxypyridine (L6) exhibited favorable effects to enhance the catalytic activity of Ru(II) catalyst for ortho C−H bond arylation of 2‐phenylpyridine by 8 folds compared to those performed without ligands. The (η6‐p‐cymene)Ru – L6 system also exhibited enhanced catalytic activity for ortho C−H bond arylation of 2‐phenylpyridine using a variety of aryl halides. NMR and mass investigations inferred the presence of several ligand coordinated Ru(II) species, suggesting the involvement of these species in C−H bond activation reaction. Further in concurrence with the experimental findings, the density functional theory (DFT) calculations also evidenced the prominent role of 2‐hydroxypyridine based ligands in Ru(II) catalyzed C−H bond arylation of 2‐phenylpyridine with lower energy barrier for the C−H activation step. [ABSTRACT FROM AUTHOR]

It has been observed in literature that the stability of tyrosinase‐mimicked μ‐η2:η2‐peroxo‐dicopper(II) (P) can be perturbed in presence of counter‐anions (CAs) such as PhCO2−, CF3SO3−, TsO− and SbF6−. In this work, we unravel computational indicators using density functional theory to screen and study the stability of P in experimentally‐reported cases. These indicators are Gibbs energies, geometrical parameters such as distances and angles, independent gradient model based on Hirshfeld partition (IGMH) generated data, orbitals' overlap, and distortion‐interaction (DI) energies. Our DFT computed Gibbs energies indicate that P is stable in case of PhCO2− and TsO−. CF3SO3− allows P and its isoelectronic species bis‐μ‐oxo‐dicopper (O) to coexist. SbF6− shows that O is in excess. Our indicators reveal that the stability of P in case of PhCO2− and TsO− is due to the better placing of P and its CA, thus leading to better interactions and overlap of orbitals. Other indicator displays that the plane of Cu2O2 core in P is more bend in PhCO2− and TsO− cases as compared to the plane in the other two cases. In addition, the IGMH‐based indicator displays higher values in the case of PhCO2− and TsO− than the other CAs. [ABSTRACT FROM AUTHOR]

The chemoselective hydroboration of aldehydes and ketones, catalyzed by Zinc(II) complexes [κ2‐(PyCH=NR)ZnX2] [R=CPh3, X=Cl (1) and R=Dipp (2,6‐diisoropylphenyl) and X=I (2)], in the presence of pinacolborane (HBpin) at ambient temperature and under solvent‐free conditions, which produced the corresponding boronate esters in high yield, is reported. Zinc metal complexes 1 and 2 were derived in 80–90% yield from the reaction of iminopyridine [PyCH=NR] with anhydrous zinc dichloride in dichloromethane at room temperature. The solid‐state structures of both zinc complexes were confirmed using X‐ray crystallography. Zinc complex 1 was also used as a competent pre‐catalyst in the reductive amination of carbonyl compounds with HBpin under mild and solvent‐free conditions to afford a high yield (up to 97%) of the corresponding secondary amines. The wider substrate scope of both reactions was explored. Catalytic protocols using zinc as a pre‐catalyst demonstrated an atom‐economic and green method with diverse substrates bearing excellent functional group tolerance. Computational studies established a plausible mechanism for catalytic hydroboration. [ABSTRACT FROM AUTHOR]

The reaction of biphenylene ( 1) with Et2SiH2 in the presence of [Ni(PPhMe2)4] results in the formation of a mixture of 2-diethylhydrosilylbiphenyl [ 2(Et2HSi)] and 9,9,-diethyl-9-silafluorene ( 3). Silafluorene 3 was isolated in 37.5 % and 2(Et2HSi) in 36.9 % yield. The underlying reaction mechanism was elucidated by DFT calculations. 4-Methyl-9,9-diethyl-9-silafluorene ( 7) was obtained selectively from the [Ni(PPhMe2)4]-catalyzed reaction of Et2SiH2 and 1-methylbiphenylene. By contrast, no selectivity could be found in the Ni-catalyzed reaction between Et2SiH2 and the biphenylene derivative that bears tBu substituents in the 2- and 7-positions. Therefore, two pairs of isomers of tBu-substituted silafluorenes and of the related diethylhydrosilylbiphenyls were formed in this reaction. However, a subsequent dehydrogenation of the diethylhydrosilylbiphenyls with Wilkinson's catalyst yielded a mixture of 2,7-di- tert-butyl-9,9-diethyl-9-silafluorene ( 8) and 3,6-di- tert-butyl-9,9-diethyl-9-silafluorene ( 9). Silafluorenes 8 and 9 were separated by column chromatography. [ABSTRACT FROM AUTHOR]

The reaction of biphenylene ( 1) with Et2SiH2 in the presence of [Ni(PPhMe2)4] results in the formation of a mixture of 2-diethylhydrosilylbiphenyl [ 2(Et2HSi)] and 9,9,-diethyl-9-silafluorene ( 3). Silafluorene 3 was isolated in 37.5 % and 2(Et2HSi) in 36.9 % yield. The underlying reaction mechanism was elucidated by DFT calculations. 4-Methyl-9,9-diethyl-9-silafluorene ( 7) was obtained selectively from the [Ni(PPhMe2)4]-catalyzed reaction of Et2SiH2 and 1-methylbiphenylene. By contrast, no selectivity could be found in the Ni-catalyzed reaction between Et2SiH2 and the biphenylene derivative that bears tBu substituents in the 2- and 7-positions. Therefore, two pairs of isomers of tBu-substituted silafluorenes and of the related diethylhydrosilylbiphenyls were formed in this reaction. However, a subsequent dehydrogenation of the diethylhydrosilylbiphenyls with Wilkinson's catalyst yielded a mixture of 2,7-di- tert-butyl-9,9-diethyl-9-silafluorene ( 8) and 3,6-di- tert-butyl-9,9-diethyl-9-silafluorene ( 9). Silafluorenes 8 and 9 were separated by column chromatography. [ABSTRACT FROM AUTHOR]

We highlight the structural diversity of strategically designed two short peptide amphiphiles (sPAs) and describe their structure–function relationship studies. The shuffling of two key amino acids, that is, tyrosine and phenylalanine, in a designed sPA lead to a pair of constitutional isomers. Such small and strategic alteration can bring a substantial change in the self‐assembling pattern. Inspired from the naturally occurring metallopeptides, bioactive transition‐metal ions were used for constructing the unusual nanostructures. Use of appropriate metal ions created bigger differences between the properties of these isomers and hence the self‐assembly. Coordination of appropriate transition metal ions modifies the internal nanoscale structures of sPA, thus leading to the formation of vertically stacked terraced layers with decreasing size, which possess a high degree of dimensional regularity. We propose that such metal‐induced terraced nanodome‐like hierarchical self‐assembly may have relevance for specific biotechnology applications. [ABSTRACT FROM AUTHOR]