The key role of Au-substrate interactions in catalytic gold subnanoclusters

The development of gold catalysis has allowed significant levels of activity and complexity in organic synthesis. Recently, the use of very active small gold subnanoclusters (Au n, n < 10) has been reported. The stabilization of such nanocatalysts to prevent self-aggregation represents a true challenge that has been partially remediated, for instance, by their immobilization in polymer matrices. Here, we describe the transient stabilization of very small gold subnanoclusters (Au n, n < 5) by alkyl chains or aromatic groups appended to the reactive bond of simple alkynes. The superior performance toward Brønsted acid-free hydration of medium to long aliphatic alkynes (1-hexyne and 1-docecyne) and benzylacetylene with respect to phenylacetylene is demonstrated experimentally and investigated computationally. A cooperative network of dispersive Au···C-H and/or Au··· interactions, supported by quantum mechanical calculations and time-resolved luminescence experiments, is proposed to be at the origin of this stabilization. © 2017 The Author(s)

SixC1 12xO2 alloys: A possible route to stabilize carbon-based silica-like solids?

Novel extended tetrahedral forms Of CO2 have been synthesized recently under high-pressure conditions. We perform ab initio density functional theory calculations to investigate whether doping with Si can extend the stability range of such tetrahedral forms Of CO2 to ambient pressure. Calculations are performed with a simple cubic cell containing eight formula units in alpha-cristobalite-like structure. Though we find that all the SiC1-xO2 structures considered by us are thermodynamically unstable with respect to decomposition into the end members at ambient pressures, the energy differences are small, suggesting that it might be possible for such phases to exist in metastable forms. At higher pressures, the heat of formation is found to be negative. The bonding between C and O atoms is more covalent than that between Si and 0 atoms. We also find indications that some C atoms may prefer three-fold coordination at low pressur