Pazhamalai Anbarasan

Bio: Pazhamalai Anbarasan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Aryl & Cyanation. The author has an hindex of 30, co-authored 108 publications receiving 4309 citations. Previous affiliations of Pazhamalai Anbarasan include Indian Institute of Science & Leibniz Association.

Recent developments and perspectives in palladium-catalyzed cyanation of aryl halides: synthesis of benzonitriles

Abstract: The palladium-catalyzed cyanation of Ar–X (X = I, Br, Cl, OTf, and H) allows for an efficient access towards benzonitriles. After its discovery in 1973 and following significant improvements in recent decades, this methodology has become nowadays the most popular for preparation of substituted aromatic nitriles. In this critical review, we summarize the important developments in this area from 2000 until 2010 (151 references).

From Noble Metal to Nobel Prize: Palladium-Catalyzed Coupling Reactions as Key Methods in Organic Synthesis

Abstract: Palladium is known to a broad audience as a beautiful, but expensive jewellery metal. In addition, it is nowadays found in nearly every car as part of the automotive catalysts, where palladium is used to eliminate harmful emissions produced by internal combustion engines. On the other hand, and not known to the general public, is the essential role of palladium catalysts in contemporary organic chemistry, a topic which has now been recognized with the Nobel Prize for Chemistry 2010. Have a look at any recent issue of a chemical journal devoted to organic synthesis and you will discover the broad utility of palladium-based catalysts. Among these different palladium-catalyzed reactions, the so-called cross-coupling reactions have become very powerful methods for the creation of new C C bonds. In general, bond formation takes place here between less-reactive organic electrophiles, typically aryl halides, and different carbon nucleophiles with the help of palladium. Remember the situation 50 years ago, when palladium began to make its way into organic chemistry. At that time C C bond formation in organic synthesis was typically achieved by stoichiometric reactions of reactive nucleophiles with electrophiles or by pericyclic reactions. Ironically, however, oxidation catalysis was the start of today s carbon–carbon bond-forming methods: The oxidation of olefins to carbonyl compounds, specifically the synthesis of acetaldehyde from ethylene (Wacker process) by applying palladium(II) catalysts, was an important inspiration for further applications. Probably also for Richard Heck, who worked in the 1960s as an industrial chemist with Hercules Corporation. There, in the late 1960s, he developed several coupling reactions of arylmercury compounds in the presence of either stoichiometric or catalytic amounts of palladium(II). Some of this work was published in 1968 in a remarkable series of seven consecutive articles, with Heck as the sole author! Based on the reaction of phenylmercuric acetate and lithium tetrachloropalladate under an atmosphere of ethylene, which afforded styrene in 80% yield and 10% trans-stilbene, he described in 1972 a protocol for the coupling of iodobenzene with styrene, which today is known as the “Heck reaction”. A very similar reaction had already been published by Tsutomo Mizoroki in 1971. However, Mizoroki didn t follow up on the reaction and died too young from cancer. The coupling protocol for aryl halides with olefins can be considered as a milestone for the development and application of organometallic catalysis in organic synthesis and set the stage for numerous further applications. Hence, palladium-catalyzed coupling reactions were disclosed continuously during the 1970s (Scheme 1). One of the related reactions is the Sonogashira coupling of aryl halides with alkynes, typically in the presence of catalytic amounts of palladium and copper salts.

Integration of chemical catalysis with extractive fermentation to produce fuels

Abstract: The integration of biological and chemocatalytic routes can be used to convert acetone–butanol–ethanol fermentation products efficiently into ketones by palladium-catalysed alkylation, leading to a renewable method for the alternative production of petrol, jet and diesel blend stocks in high yield. Using a method that combines biological and chemical catalysis, Dean Toste and colleagues demonstrate the efficient conversion of acetone–butanol–ethanol fermentation products into ketones via a palladium-catalysed alkylation. With further improvement, this process could provide a means of selectively manufacturing gasoline, jet and diesel blend stocks from lignocellulosic and cane sugars derived from biomass at yields close to the theoretical maxima. Nearly one hundred years ago, the fermentative production of acetone by Clostridium acetobutylicum provided a crucial alternative source of this solvent for manufacture of the explosive cordite. Today there is a resurgence of interest in solventogenic Clostridium species to produce n-butanol and ethanol for use as renewable alternative transportation fuels1,2,3. Acetone, a product of acetone–n-butanol–ethanol (ABE) fermentation, harbours a nucleophilic α-carbon, which is amenable to C–C bond formation with the electrophilic alcohols produced in ABE fermentation. This functionality can be used to form higher-molecular-mass hydrocarbons similar to those found in current jet and diesel fuels. Here we describe the integration of biological and chemocatalytic routes to convert ABE fermentation products efficiently into ketones by a palladium-catalysed alkylation. Tuning of the reaction conditions permits the production of either petrol or jet and diesel precursors. Glyceryl tributyrate was used for the in situ selective extraction of both acetone and alcohols to enable the simple integration of ABE fermentation and chemical catalysis, while reducing the energy demand of the overall process. This process provides a means to selectively produce petrol, jet and diesel blend stocks from lignocellulosic and cane sugars at yields near their theoretical maxima.

Well-Defined Iron Catalyst for Improved Hydrogenation of Carbon Dioxide and Bicarbonate

Abstract: The most efficient, stable, and easy-to-synthesize non-noble metal catalyst system for the reduction of CO2 and bicarbonates is presented. In the presence of the iron(II)-fluoro-tris(2-(diphenylphosphino)phenyl)phosphino]tetrafluoroborate complex 3, the hydrogenation of bicarbonates proceeds in good yields with high catalyst productivity and activity (TON > 7500, TOF > 750). High-pressure NMR studies of the hydrogenation of carbon dioxide demonstrate that the corresponding iron-hydridodihydrogen complex 4 is crucial in the catalytic cycle.

Introduction of Fluorine and Fluorine-Containing Functional Groups

Abstract: Over the past decade, the most significant, conceptual advances in the field of fluorination were enabled most prominently by organo- and transition-metal catalysis. The most challenging transformation remains the formation of the parent C-F bond, primarily as a consequence of the high hydration energy of fluoride, strong metal-fluorine bonds, and highly polarized bonds to fluorine. Most fluorination reactions still lack generality, predictability, and cost-efficiency. Despite all current limitations, modern fluorination methods have made fluorinated molecules more readily available than ever before and have begun to have an impact on research areas that do not require large amounts of material, such as drug discovery and positron emission tomography. This Review gives a brief summary of conventional fluorination reactions, including those reactions that introduce fluorinated functional groups, and focuses on modern developments in the field.

Catalysis for fluorination and trifluoromethylation

Abstract: Recent advances in catalysis have made the incorporation of fluorine into complex organic molecules easier than ever before, but selective, general and practical fluorination reactions remain sought after. Fluorination of molecules often imparts desirable properties, such as metabolic and thermal stability, and fluorinated molecules are therefore frequently used as pharmaceuticals or materials. But the formation of carbon-fluorine bonds in complex molecules is a significant challenge. Here we discuss reactions to make organofluorides that have emerged within the past few years and which exemplify how to overcome some of the intricate challenges associated with fluorination.

Frontiers, Opportunities, and Challenges in Biochemical and Chemical Catalysis of CO2 Fixation

Abstract: Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.