V imido alkylidenes have been applied for the ringopening metathesis polymerization involving cyclic olefins. However, those complexes found limited application in reactions with acyclic terminal olefins due to instability toward ethylene. Experimental and theoretical studies show that the β-hydride elimination from unsubstituted metallacyclobutene is the primary decomposition pathway in those systems. Herein, we report the synthesis of the first catalytically active V oxo alkylidene, VO(CHSiMe 3 )(PEt 3 ) 2 Cl, which exhibits the highest reported productivity with various terminal olefins in ring-closing metathesis reactions among known V catalysts. Presented DFT studies indicate that β-hydride elimination is significantly disfavored for V oxo species.
Vanadium bis-phosphine imido and
oxo chloride alkylidenes have
been extensively applied in the ring-closing metathesis of various
acyclic olefins. However, their reactions involving ethylene have
shown limited productivity due to rapid decomposition. The primary
degradation pathway involving V bis-phosphine imido complexes is β-H
elimination at an unsubstituted metallacyclobutane. In contrast, β-H
elimination is disfavored for V oxo species, but bimolecular decomposition
precludes its high productivity. Herein, we present the synthesis
of V imido NHC complexes that are the most productive V catalysts
toward various terminal olefins in ring-closing metathesis reactions.
Experimental and computational studies suggest that β-H elimination
and bimolecular decomposition are disfavored for V imido NHC complexes.
Cadmium selenide nanomaterials are very important materials in photonics, catalysis, and biomedical applications due to their optical properties that can be tuned through size, shape, and surface passivation. In this report, static and ab initio molecular dynamics density functional theory (DFT) simulations are used to characterize the effect of ligand adsorption on the electronic properties of the (110) surface of zinc blende and wurtzite CdSe and a (CdSe) 33 nanoparticle. Adsorption energies depend on ligand surface coverage and result from a balance between chemical affinity and ligand−surface and ligand−ligand dispersive interactions. In addition, while little structural reorganization occurs upon slab formation, Cd•••Cd distances become shorter and the Se−Cd−Se angles become smaller in the bare nanoparticle model. This originates mid-gap states that strongly influence the absorption optical spectra of nonpassivated (CdSe) 33 . Ligand passivation on both zinc blende and wurtzite surfaces does not induce a surface reorganization, and thus, the band gap remains nonaffected with respect to bare surfaces. In contrast, structural reconstruction is more apparent for the nanoparticle, which significantly increases its highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) gap upon passivation. Solvent effects decrease the band gap difference between the passivated and nonpassivated nanoparticles, the maximum of the absorption spectra being blue-shifted around 20 nm by the effect of the ligands. Overall, calculations show that flexible surface cadmium sites are responsible for the appearance of mid-gap states that are partially localized on the most reconstructed regions of the nanoparticle that can be controlled through appropriate ligand adsorption.
The performance of Ru-based nanoparticles (NPs) in the hydrogen evolution reaction (HER) relies on both their structural properties and the oxidation state of the metal. Herein, the versatility of the...
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