Addition of Sn–O^<i>i</i>Pr across a CC Bond: Unusual Insertion of an Alkene into a Main-Group-Metal–Alkoxide Bond

An example of unusual addition of a main-group-metal alkoxide across an alkene CC bond was demonstrated with a dimethylvinylsilyl-substituted Sn-POSS complex (POSS = incompletely condensed polyhedral oligomeric silsesquioxane). The structure of the pentacoordinated Sn chelate product was confirmed by ¹H, ¹³C, and ¹¹⁹Sn NMR and ESI-MS

Microkinetic Modeling of Homogeneous and Gold Nanoparticle-Catalyzed Oxidation of Cyclooctene

Small gold nanoparticles (AuNPs) have recently shown potential to act as a catalyst for oxidation reactions mediated by free radicals, with their role postulated to be facilitating hydrogen abstraction by gold superoxo species and/or activation of hydroperoxides. Cyclooctene oxidation using molecular oxygen as the oxidant at 373 K showed high selectivity to the epoxide product, cyclooctene oxide, with either <i>tert</i>-butyl hydroperoxide as an initiator or in the presence of small AuNPs (5–8 atoms). While previous studies have investigated the mechanism leading to high epoxide selectivity using density functional theory, a full microkinetic model was developed in this work using automated network generation to determine the relative contributions of elementary reactions and the role of AuNPs. A cycle of radical addition of peroxy and alkoxy radicals with subsequent epoxidation reactions can justify the observed activity and selectivity to epoxide at multiple temperatures and initiator concentrations. The alcohol, ketone, and hydroperoxide minor products are formed when the peroxy and alkoxy radicals perform hydrogen abstraction or β-scission. The overall selectivity is determined by the competition between the addition and hydrogen abstraction reactions. With the underlying homogeneous reaction model validated, the effect of the AuNPs was determined through an expanded model that includes cycles for both hydrogen abstraction by superoxo gold species and hydroperoxide decomposition via species derived from AuNPs. The model suggests that hydrogen abstraction by the superoxo gold species dominates at short times compared to homogeneous initiation, increasing the activity during the induction period and reducing the time before radical chain oxidation commences. On the time scale of an hour, hydroperoxide decomposition is significantly catalyzed by the presence of gold species, increasing the overall rate of chain propagation

Generating and Stabilizing Co(I) in a Nanocage Environment

A discrete nanocage of core–shell design, in which carboxylic acid groups were tethered to the core and silanol to the shell interior, was found to react with Co₂(CO)₈ to form and stabilize a Co­(I)–CO species. The singular CO stretching band of this new Co species at 1958 cm^–1 and its magnetic susceptibility were consistent with Co­(I) compounds. When exposed to O₂, it transformed from an EPR inactive to an EPR active species indicative of oxidation of Co­(I) to Co­(II) with the formation of H₂O₂. It could be oxidized also by organoazide or water. Its residence in the nanocage interior was confirmed by size selectivity in the oxidation process and the fact that the entrapped Co species could not be accessed by an electrode

Supported Tetrahedral Oxo-Sn Catalyst: Single Site, Two Modes of Catalysis

Mild calcination in ozone of a (POSS)-Sn-(POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV–vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Brønsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn–O–Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions

Acceptorless Dehydrogenative Coupling of Neat Alcohols Using Group VI Sulfide Catalysts

Group VI sulfides were synthesized via coprecipitation of elemental sulfur and metal hexacarbonyl and characterized with XRD, XPS, and TEM. These materials were then demonstrated as active catalysts for the acceptorless dehydrogenative coupling of neat ethanol to ethyl acetate, rapidly reaching equilibrium conversion and up to 90% selectivity. Other primary alcohols form the corresponding esters, while diols formed the corresponding cyclic ethers and oligomers