Mild Epoxidation of Allylic Alcohols Catalyzed by Titanium(III) Complexes: Selectivity and Mechanism

Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study

In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non-catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non-catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions.

Rational Design of Self-Supported CuO x -Decorated Composite Films as an Efficient and Easy-Recycling Catalyst for Styrene Oxidation

The applications of graphene-based materials in catalysis are limited by their strong tendency to aggregate, which may lead to a decrease in active sites. Herein, we propose a facile and controllable strategy to fabricate a series of heterogeneous catalysts with a unique nanostructure wherein CuO _x -decorated reduced graphene oxide (rGO) sheets are incorporated into a solid matrix composed of poly(vinylpyrrolidone) (PVP) and carboxymethyl cellulose (CMC). The resultant materials are self-supported films and could be directly used as catalysts for the liquid-phase oxidation of styrene without the requirement for extra substrates. The employment of PVP-CMC (PC) as the support for CuO _x -decorated rGO sheets successfully inhibits their aggregation. Benefiting from the dispersion of copper species, these films exhibit good catalytic activity and recyclability under mild reaction conditions. Especially, they can be conveniently removed from the reaction mixture by tweezers due to their structural stability. For catalyzing multiple reactions with high efficiency and facile recyclability, this study offers a universal strategy to design heterogeneous catalysts based on graphene materials and provides a promising platform.

The Proven Versatility of Cp2TiCl

In the last two decades, titanocene monochloride has been postulated as a monoelectronic transfer reagent capable of catalyzing an important variety of chemical transformations. In this Perspective, our contributions to this growing field of research are summarized and analyzed. Especially known have been our contributions in C-C bond formation reactions, hydrogen-atom transfer from water to radicals, and isomerization reactions, as well as the development of a catalytic cycle that has subsequently allowed the preparation of a great variety of natural terpenes. It is also worth mentioning our contribution in the postulation of this single-electron transfer agent (SET) as a new green catalyst with a broad range of applications in organic and organometallic chemistry. The most significant catalytic processes developed by other research groups are also briefly described, with special emphasis on the reaction mechanisms involved. Finally, a reflection is made on the future trends in the research of this SET, aimed at consolidating this chemical as a new green reagent that will be widely used in fine chemistry, green chemistry, and industrial chemical processes.

Theoretical Studies of the Zeolite-Y Encapsulated Chlorine-Substituted Copper(II)phthalocyanine Complex on the Formation Glycidol from Allyl Alcohol

Density functional theory (DFT) used to study the encapsulation of copper(II)phthalocyanine and chlorine-substituted copper(II)phthalocyanine to a zeolite-Y framework. Changes occurring in the redox properties, as well as the red shift of the time-dependent DFT (TD-DFT) spectra, point out the influence of encapsulation on the geometric parameters of the complexes. Also, the TD-DFT calculations show good agreement with the energy changes occurred in the highest occupied molecular orbital and lowest unoccupied molecular orbital. DFT-based descriptors are used for scrutinizing the reactivity of the encapsulated complexes and a mechanism of the glycidol formation is proposed based on the energetics involved in the transformation.