Rhenium oxo complexes in catalytic oxidations

Synthesis of 1-Aryltetralins via Re2O7/HReO4 Mediated Intramolecular Hydroarylations

Here, we describe highly efficient intramolecular hydroarylations mediated by Re2O7/HReO4. Styrene derivatives of different electronic properties have been activated to effect a challenging intramolecular hydroarylation for the facile access to various substituted 1-aryltetralin structures. This method is characterized by mild reaction conditions, broad substrate scope, high chemical yields, and 100% atom economy. The potential synthetic application of this methodology was exemplified by the efficient total synthesis of an isoCA-4 analogue.

Rhenium-catalysed reactions in chemical synthesis: selected case studies

This Perspective presents and discusses a selection of examples that reinforce the enabling and distinctive reactivity provided by homogeneous rhenium catalysis in chemical synthesis. Specifically, the ability for lower oxidation...

Methyltrioxorhenium (MTO) catalysis in the epoxidation of alkenes: a synthetic overview

Epoxides are biologically important moiety that is also used as synthetic intermediates. This review aims to present the up-to-date advancements in methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes using diverse oxidizing agents.

A recyclable cobalt(iii)–ammonia complex catalyst for catalytic epoxidation of olefins with air as the oxidant

A recyclable [Co(NH₃)₆]Cl₃ complex was synthesized to catalyze the epoxidation of α-pinene. With air as the oxidant, [Co(NH₃)₆]Cl₃ obtained 97.4% conversion of α-pinene and 98.3% selectivity of epoxide.

Rhenium in the core of porphyrin and rhenium bound to the periphery of porphyrin: synthesis and applications

An overview of most of the well known rhenium porphyrins (rhenium in the core of porphyrins) is presented here reviewing their synthesis, coordination chemistry, and applications. The important features of oxorhenium(v) porphyrins are discussed elaborately taking into account their application in epoxidation reaction. Moreover, the chemistry of some recently known porphyrin-Re conjugates (rhenium bound to the periphery of porphyrin) is reported considering their applications in the photochemical carbon dioxide reduction process and photodynamic therapy. The number of well characterized rhenium porphyrinoids are limited but they show interesting diverse properties, some of which are also discussed in this review.

Catalytic hydrogenation of carboxylic acids using low-valent and high-valent metal complexes

Carboxylic acids are ubiquitous in bio-renewable and petrochemical sources of carbon.

Catalytic transformation of functionalized carboxylic acids using multifunctional rhenium complexes

Carboxylic acids (CAs) are one of the most ubiquitous and important chemical feedstocks available from biorenewable resources, CO₂, and the petrochemical industry. Unfortunately, chemoselective catalytic transformations of CH_nCO₂H (n = 1–3) groups into other functionalities remain a significant challenge. Herein, we report rhenium^V complexes as extremely effective precatalysts for this purpose. Compared to previously reported heterogeneous and homogeneous catalysts derived from high- or low-valent metals, the present method involves a α-C–H bond functionalization, a hydrogenation, and a hydrogenolysis, which affords functionalized alcohols with a wide substrate scope and high chemoselectivity under relatively mild reaction conditions. The results represent an important step toward a paradigm shift from ‘low-valent’ to ‘high-valent’ metal complexes by exploring a new portfolio of selective functional group transformations of highly oxygenated organic substrates, as well as toward the exploitation of CAs as a valuable biorenewable feedstock.

Acetogenins from Annonaceae

In recent decades, annonaceous acetogenins have become highly studied plant secondary metabolites in terms of their isolation, structure elucidation, synthesis, biological evaluation, mechanism of action, and toxicity. The aim of the present contribution is to summarize chemical and biological reports published since 1997 on annonaceous acetogenins and synthetic acetogenin mimics. The compounds are considered biologically in terms of their cytotoxicity for cancer cell lines, neurotoxicity, pesticidal effects, and miscellaneous activities.

The unexpected mechanism underlying the high-valent mono-oxo-rhenium(V) hydride catalyzed hydrosilylation of C=N functionalities: insights from a DFT study

In this study, we theoretically investigated the mechanism underlying the high-valent mono-oxo-rhenium(V) hydride Re(O)HCl2(PPh3)2 (1) catalyzed hydrosilylation of C=N functionalities. Our results suggest that an ionic S(N)2-Si outer-sphere pathway involving the heterolytic cleavage of the Si-H bond competes with the hydride pathway involving the C=N bond inserted into the Re-H bond for the rhenium hydride (1) catalyzed hydrosilylation of the less steric C=N functionalities (phenylmethanimine, PhCH=NH, and N-phenylbenzylideneimine, PhCH=NPh). The rate-determining free-energy barriers for the ionic outer-sphere pathway are calculated to be ∼28.1 and 27.6 kcal mol(-1), respectively. These values are slightly more favorable than those obtained for the hydride pathway (by ∼1-3 kcal mol(-1)), whereas for the large steric C=N functionality of N,1,1-tri(phenyl)methanimine (PhCPh=NPh), the ionic outer-sphere pathway (33.1 kcal mol(-1)) is more favorable than the hydride pathway by as much as 11.5 kcal mol(-1). Along the ionic outer-sphere pathway, neither the multiply bonded oxo ligand nor the inherent hydride moiety participate in the activation of the Si-H bond.

Mechanistic insights into hydrogen generation for catalytic hydrolysis and alcoholysis of silanes with high-valent oxorhenium(v) complexes

The ionic outer-sphere pathway, which proceeds via the nucleophilic anti attack of water or alcohol on the silicon atom is the most favorable pathway for the high-valent oxorhenium(v) complex-catalyzed hydrolysis/alcoholysis of organosilanes.

Re2O7catalyzed dienone-phenol rearrangement

The dienone-phenol rearrangement of 4,4-disubstituted cyclohexadienones to multi-substituted phenols is achieved by employing Re₂O₇as the catalyst.

Methyltrioxorhenium-catalyzed highly selective dihydroxylation of 1,2-allenylic diphenyl phosphine oxides

Methyltrioxorhenium catalyzed highly selective dihydroxylation of allenes – a novel catalytic protocol for the synthesis of α-hydroxyl ketones.

Mechanistic insights into B–H bond activation with the high-valent oxo-molybdenum complex MoO2Cl2

The ionic mechanistic model involving the heterolytic cleavage of the B–H bond is slightly energetically favorable than the [2+2] addition mechanism for the high-valent oxo-molybdenum complex MoO₂Cl₂activating the B–H bond.