Catalytic dehydrogenative cross-coupling: forming carbon-carbon bonds by oxidizing two carbon-hydrogen bonds

Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific C-H bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site. A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of C-H bond functionalization reactions towards complex molecule synthesis. Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rh-catalyzed methods for C-H bond functionalization stand out, with several syntheses being described in the literature that utilize C-H bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.

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Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1–3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the s...

Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities

Aromatic substrates with oxygen- and nitrogen-containing substituents undergo oxidative coupling with alkynes and alkenes under rhodium catalysis through regioselective C-H bond cleavage. Coordination of the substituents to the rhodium center is the key to activate the C-H bonds effectively. Various fused-ring systems can be constructed through these reactions.

/pdf/oxidative-coupling-of-aromatic-substrates-with-alkynes-and-38wvfopo33.pdf

Oxidative Coupling of Aromatic Substrates with Alkynes and Alkenes under Rhodium Catalysis

Catalytic transformation of ubiquitous C–H bonds into valuable C–N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C–H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

Transition Metal-Catalyzed C–H Amination: Scope, Mechanism, and Applications

The development of an efficient catalytic activation (cleavage) system for C−H and C−C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C−H and C−C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate. In this Account, we describe our entire efforts to activate C−H or C−C bonds adjacent to carbonyl groups by employing a new concept of metal−organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C−C triple bond cleavage, hydrative dime...

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

Intermolecular hydroacylation by transition-metal complexes

The dehydroformylation of aldehydes to generate olefins occurs during the biosynthesis of various sterols, including cholesterol in humans Here, we implement a synthetic version that features the transfer of a formyl group and hydride from an aldehyde substrate to a strained olefin acceptor A Rhodium (Xantphos)(benzoate) catalyst activates aldehyde carbon-hydrogen (C–H) bonds with high chemoselectivity to trigger carbon-carbon (C–C) bond cleavage and generate olefins at low loadings (03 to 2 mole percent) and temperatures (22° to 80°C) This mild protocol can be applied to various natural products and was used to achieve a three-step synthesis of (+)-yohimbenone A study of the mechanism reveals that the benzoate counterion acts as a proton shuttle to enable transfer hydroformylation

http://science.sciencemag.org/content/sci/347/6217/56.full.pdf

Rh-catalyzed C–C bond cleavage by transfer hydroformylation

Novel Au25(C6S)17PyS clusters (pyrene-functionalized Au25 clusters) showing interesting electrochemical and optical properties are synthesized and characterized. Significant fluorescence quenching is observed for pyrene attached to Au25 clusters, suggesting strong excited-state interactions. Time-resolved fluorescence upconversion and transient absorption measurements are utilized to understand the excited-state dynamics and possible interfacial electron- and energy-transfer pathways. Electrochemical investigations suggest the possibility of electron transfer from Au25 clusters to the attached pyrene. Fluorescence upconversion measurements have shown faster luminescence decay for the case of pyrene attached to Au25 clusters pointing toward ultrafast photoinduced electron/energy-transfer pathways. Femtosecond transient absorption measurements have revealed the presence of the anion radical of pyrene in the excited-state absorption, suggesting the directional electron transfer from Au25 clusters to pyrene. ...

Jung‐Woo Park

Papers

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

Intermolecular hydroacylation by transition-metal complexes

Rh-catalyzed C–C bond cleavage by transfer hydroformylation

Directional electron transfer in chromophore-labeled quantum-sized Au 25 clusters: Au25 as an electron donor

Post-grafting of silica surfaces with pre-functionalized organosilanes: new synthetic equivalents of conventional trialkoxysilanes.