Review: active homogeneous reagents and catalysts in n -alkane activation (original) (raw)
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Nature chemistry, 2018
C-H functionalization represents a promising approach for the synthesis of complex molecules. Instead of relying on modifying the functional groups present in a molecule, the synthetic sequence is achieved by carrying out selective reactions on the C-H bonds, which traditionally would have been considered to be the unreactive components of a molecule. A major challenge is to design catalysts to control both the site- and stereoselectivity of the C-H functionalization. We have been developing dirhodium catalysts with different selectivity profiles in C-H functionalization reactions with donor/acceptor carbenes as reactive intermediates. Here we describe a new dirhodium catalyst capable of the functionalization of non-activated primary C-H bonds with high levels of site selectivity and enantioselectivity.
Angewandte Chemie International Edition
Selective catalysts for sustainable oxidation of alkanes are highly demanded because of the abundance of these molecules in the environment, the possibility to transform them into higher-value compounds, such as chemicals or synthetic fuels, and the fact that, kinetically speaking, this is a difficult reaction. Numerous chemical and biological catalysts have been developed in the lasts decades for this purpose, rendering the overview over this field of chemistry difficult. After giving a definition of the ideal catalyst for alkane oxyfunctionalization, this review aims to present the catalysts available today that are closest to ideal.
Advances in Development of C–H Activation/Functionalization Using a Catalytic Directing Group
The transition metal catalyzed direct site‐selective carbon –hydrogen functionalization is ubiquitous in organic synthesis and has reached an impressive level of sophistication and efficiency emerging as a powerful synthetic strategy for C–C bond and C–X bond formation to access various useful arylated organic molecules. For the past two decades, directing group strategy has been used for selective activation and functionalization of certain inert C–H bonds. Despite the enormous development in this field, still, the majority of systems require two redundant steps, i. e. installation and removal of DGs. To overcome these limitations, recently, traceless and multitasking groups were invented as a partial solution to DG release however installation still remains unsolved. Ideally, use of the catalytic directing group, which can be reversibly linked to the substrate and can serve as an efficient directing role would circumvent this problem and is considered as one of the most efficient and powerful strategies for the non‐activated C–H functionalization (C(sp2)–H or C(sp3)–H). In this review, we describe the enormous advances in this field for direct selective C–H functionalization without involving additional steps, i. e. installation and removal of directing groups and also discuss less explored but significant non‐covalent interactions such as hydrogen bonding or ion pairing, which helps to control the selectivity of a substrate in a catalytic organic reaction.
Journal of Molecular Catalysis A: Chemical, 2006
The direct, low temperature conversion of hydrocarbons to functionalized products using novel, single site catalysts could lead to technological advances that redefine the landscape of the current materials and energy industries. Natural gas continues to represent a vast source of untapped hydrocarbons around the globe that has the potential to replace or augment petroleum as the raw material for materials and energy. Its abundance has garnered much interest in the scientific community as groups have focused on the catalytic conversion of its major component, methane, to functionalized products. The key requirements is to design new catalysts for the oxidative functionalization of methane that operate at lower temperatures and that also meet the basic requirements of selectivity, rate, and lifetime that characterize useful catalysts. Recent advances in the field of hydrocarbon CH activation have shown the potential for transition metal based coordination catalysts to meet these requirements. Described herein are recent advances in designing catalysts based on the CH activation reaction that address the basic requirements for practical systems with emphasis on the issues that have prevented promising reported systems from becoming commercially viable.
Current Organic Chemistry, 2011
Heterocyclic compounds are of paramount importance in essentially all fields of chemistry and in our daily life. Therefore, the synthesis and modification of such compounds is an ever expanding field in synthetic chemistry. In recent years, all synthetic efforts were guided increasingly by the search for more atom efficient and economical methods. Transition metal catalyzed C-H activation reactions have proved to provide both: i) an increased atom efficiency since the number of functional groups required to form a desired bond can be reduced due to substitution of at least one functional group usually required in cross-coupling reactions by a C-H bond, and ii) shorter overall reaction times and a reduced number of synthetic steps which ultimately leads to more economical processes. Additionally, the C-H activation approach can be considered as an effort towards a greener chemistry, since the reduction in the number of synthetic steps in the majority of cases leads to a decrease in the amount of waste produced (silica gel, solvents, etc.) and energy consumed. The focus of this review is on the direct functionalization of both saturated and unsaturated heterocycles. Methods for the formation of CC and carbon-heteroatom bonds will be discussed. In the case of saturated heterocycles, another focus will be put on the stereospecific functionalization of such building blocks. Dedicated to Emeritus Prof. Fritz Sauter on the occasion of his 80 th birthday.
Enhancing the Enantioselectivity of Novel Homogeneous Organometallic Hydrogenation Catalysts
Angewandte Chemie International Edition, 2003
The exigent need to develop new asymmetric hydrogenation catalysts is universally acknowledged, and many new feasible strategies for the design and synthesis of such catalysts continue to be proposed. Herein, in addition to describing a new set of efficient, diamino-type ligands for a central rhodium or palladium ion that leads to good enantioselective (ee) performance, homogeneously, we also show that significant improvement in the stereoselectivity of the organometallic catalyst may be achieved by heterogenizing it at the inner walls of a mesoporous silica so that advantage is taken of the spatial restrictions imposed by the concave surface at which we have located the active center.
Catalysis Letters, 2011
Selective catalysts that activate small molecules such as hydrocarbons, dioxygen, water, carbon dioxide and dihydrogen are central to new technologies for the use of alternative energy sources. For example, controlled hydrocarbon functionalization can lead to high impact technologies, but such catalysts require a level of molecular control beyond current means. The Center for Catalytic Hydrocarbon Functionalization facilitates collaborations among research groups in catalysis, materials, electrochemistry, bioinorganic chemistry and quantum mechanics to develop, validate and optimize new methods to rearrange the bonds of hydrocarbons, activate and transform water and carbon dioxide, implement enzymatic strategies into synthetic systems and design optimal environments for catalysis.
RECENT PROGRESS IN OXIDATION OF n-ALKANES BY HETEROGENEOUS CATALYSIS
Many heterogeneous catalysts are known to convert alkanes at high temperatures to a variety of products, but unfortunately most of these systems are not amenable to catalytic transformations since the reactive intermediate species are converted to different products in low yields. It is also observed that the product distribution in these reactions strongly depends on the parametric conditions. The commercial interest as the industrially applicable process for the selective oxidation of n-alkanes to give alcohols and carbonyl compounds is AKELLA SIVARAMAKRISHNA et al. 76 gaining a lot of significance in modern catalytic chemistry. Also, the production of hydrogen gas from saturated hydrocarbons is one of the focus areas in the present scenario. This review article mainly focuses on important methodologies adopted to activate CH bonds of n-alkanes by various heterogeneous catalysts by highlighting their strengths as well as drawbacks. As there is a demand in searching for the new te...