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CYCLPENTADIENYL MLYBDENUM ACETYLIDE CMPLEXES AS NVEL CATALYST FR XIDATIN REACTINS A THESIS SUBMITTED T THE UNIVERSITY F PUNE FR THE DEGREE F DCTR F PHILSPHY IN CHEMISTRY BY Research Student Ankush V. Biradar Research guide Dr. Shubhangi B. Umbarkar CATALYSIS DIVISIN NATINAL CHEMICAL LABRATRY PUNE , INDIA Dec 2008 CERTIFICATE Certified that the work incorporated in the thesis entitled Cyclopentadienyl Molybdenum Acetylide Complexes As Novel Catalysts For xidation Reactions submitted by Ankush V. Biradar for the Degree of Doctor of Philosophy, in Chemistry was carried out by the candidate under my supervision in the Catalysis Division, National Chemical Laboratory, Pune , India. Materials obtained from other sources have been duly acknowledged in the thesis. Date : Dr. Shubhangi B. Umbarkar (Research Supervisor) DECLARATIN I hereby declare that the thesis entitled Cyclopentadienyl Molybdenum Acetylide Complexes As Novel Catalysts For xidation Reactions submitted for my Ph.D. degree to the University of Pune has been carried out at National Chemical Laboratory, under the guidance of Dr. Shubhangi B. Umbarkar. The work is original and has not been submitted in part or full by me for any degree or diploma to this or any other University. Date: Ankush V. Biradar (Research Student) Dedicated to my Parents and Teachers I know quite certainly that I myself have no special talent; curiosity, obsession and dogged endurance, combined with selfcriticism, have brought me to my ideas. -- Albert Einstein.. Suits me as well!!! Acknowledgments It is a great privilege for me to be a student of Dr. Shubhangi B. Umbarkar, my supervisor, who has suggested the problem, offered constructive criticism and encouragement at every stage of my research work. I pay my gratitude to her, in particular for her valuable guidance, her meticulous attention to this work and her exemplary editing of thesis. She has provided many opportunities for me to increase my abilities as researcher and responsibilities as a team member. My most sincere and heartfelt thanks go to Dr.Mohan K. Dongare, who whole heartedly helped me at every stage of my work. His outstanding source of knowledge, numerous scientific discussions and practicability made large impact on my thesis. My thanks goes to Dr. S. Sivaram, Director, Dr. B. D. Kulkarni Dy.director NCL for allowing me to carry out the research work at NCL and CSIR, New Delhi, INDIA, for the financial support in the form of senior research fellowship and DST for financial support for research project, SAIF, Lucknow for providing mass spectrum. Thanks to Leon Gengembre, Martin Trentesaux and Marie Angelique Languille, UCCS, University of Lille 1, France for XPS studies. I am thankful to Dr. Rajiv Kumar, former Head, Catalysis Division, NCL for providing the permission for my work. It gives me a great pleasure to express my deep sense of gratitude and indebtedness to Dr. Hegde, Dr. Satyanarayana, Dr. Vedavati Puranik, Dr. Pardhy, Dr. Deshpande, Dr. Nandini, Dr. kinge, Dr. Vijaymohanan, Ms.Violet, Mr. Niphadkar, Mr. Tejas, Mr. Purushothaman, Mr. Dipak Mr. Madhu, and all the other scientific and non-scientific staff of NCL for their help and inspiring guidance and suggestions in carrying out the research work. Dr. Martin, Dr. Udo, Dr. Narayana, Dr. Jonge, Dr. Illyas and all members of Leibniz institute for catalysis Rostock University Germany, Pratap and Ankush who made my staying very easy in Germany thanks a lot. I sincerely thank my labmates Sanyo, Trupti, Vaibhav, Vincent, Nishita, Rajani and Amol. I enjoyed a lot scientific co-operation with Bhaskar with fruitful results. Many many thanks. My special thanks to Amrut with whom I shared a cup of tea, debating and offering me a helping hand when needy time. Dr. Mahesh, Dr. Rohit, Dr. Amit, Dr. Suman, Dr. Ankur, Ramakant, Atul, Dr. Devu, Ganesh, Dr. Sachin, Dr. Pallavi, Selva, Surendran, Dr. Pranjal and many others for their cooperation, encouragement, invaluable help and moral support in one way or other, which made my work much easier. I also wish to Thank to Dr. R. V. Chudhari, Savita, Dr. Kelkar, Dr. Gupte, Dr. Rode and Mr. Joshi. Prof. Bandgar, Dr. kamble. I cannot forget the rejoice full moments with Dr.Yogesh Dr. Sunil, Dr. Anand, Dr. Charu, Dr. Nandu, Mahesh, Anamica, Atul, Makarand, Samadhan, Lalita, Amit, Dr. Debu, Dr. Sarkar, Mahesh Bhure, JP, Vikas and many others. All my sincere thanks to all NCL mates especially Satish, Kishan, Sudhir, Bapu Dr. Namdev, Bhalchandra, Dr. Mahima, Dhanraj, Laximan, Mukund, Arvind, Prasana kumar, Tanaji. Rajesh and many more. I would also like to thank my friends Amit Mehtre, Anand and vaishali Jadhav and Parag for their presence in my life. It would be very difficult to stay in NCL campus without support of Rajaput kaku, maushi, Mr. Khandekar and Mr.Pagare thankful to all of them. The words are not enough to express all my love and thankfulness towards parents and specially my brother (dada & vahini) who was behind me in every good and bad time and kept inspiring me all the way. I would like to express my deep felt gratitude to kaka, Bhau and Baspure. I could not have completed my research work without their help and blessings. Lastly, I would like to thank my wife Archana. We've endured a lot together throughout our relationship and the recent difficulty and uncertainty of finding a job. Still, through it all, she has been a loving companion and my best friend. Ankush V. Biradar Table of Contents Abbreviations Chapter 1 Introduction: rganometallic molybdenum complexes and oxidation reactions Introduction Catalysis rganometallic chemistry and homogeneous catalysis Application of organometallic catalysts in the chemical 8 industry 1.5 Heterogenization of homogeneous catalysts xidation reactions: A challenge Scope and contents of thesis References 24 Chapter 2 Synthesis and characterization of cyclopentadienyl Molybdenum acetylide complexes Introduction Experimental Results and discussions Characterization of formation of oxo-peroxo species Summary and conclusions References 59 Chapter 3 Selective cis-dihydroxylation of alkenes using a molybdenum 62 acetylide catalyst 3.1 Introduction Experimental Results and discussion xidation of different alkenes Reaction mechanism 77 3.6 Summary and conclusions References 86 Chapter 4 xidation of amines, alcohols and sulfide using 90 cyclopentadienyl molybdenum (VI) oxo peroxo complex 4.1. Introduction 92 Part A: Selective N-oxidation of aromatic amines to nitroso 92 derivatives 4.2 Introduction Experimental Result and discussion xidation of substitute anilines Mechanism Summary and conclusions 104 Part B: Solvent free oxidation of aromatic primary alcohols to 104 aldehydes 4.8 Introduction Experimental Results and discussion The scope of substrate Summary and conclusions 110 Part C: Selective oxidation of sulfides to Sulfoxides or 111 Sulfones 4.13 Introduction xidation of refractory sulfides Experimental Result and discussion Substrate scope Catalyst recycle study xidation of thioanisole with heterogenized catalyst Summary and conclusions References 124 Chapter 5 Dioxo cyclopentadienyl molybdenum acetylide catalyzed 130 oxyfunctionazation of hydrocarbons 5.1 Introduction Experimental Results and Discussion Summary and conclusions References 144 Summary conclusions and future prospects 147 Selected analytical data 152 Publication list 162 Corrigendum 164 ABBREVIATINS Cp CP MAS NMR EDAX FID FT-IR GC GCMS NMR TBHP TLC TN TF TS UV-Vis XPS XRD s 4 NM Cat h Mol THF δ ν Cyclopentadienyl anion Cross Polarization Magic Angle Spinning NMR Energy Dispersive X-ray spectroscopy Flame Ionized Detector Fourier-Transform Infrared Gas Chromatography Gas Chromatography-Mass Spectroscopy Nuclear Magnetic Resonance tert- Butyl Hydrogen Peroxide Thin Layer Chromatography Turn ver Number Turn ver Frequency Time n Stream Ultra Violet-Visible X-ray Photoelectron Spectroscopy X-ray Diffraction smium Tetroxide N- Methymorpholine N-oxide Catalyst, Catalytic Hour (s) Mole Tetrahydrofuran Chemical Shift Wave Number Chapter-1 Introduction Chapter- 1 Introduction: rganometallic molybdenum complexes and oxidation reactions Catalysis Division, National Chemical Laboratory, Pune 1 Chapter-1 Introduction 1. Introduction: rganometallic molybdenum complexes and oxidation reactions Abstract: The oxidation of organic compounds with high selectivity is of extreme importance in synthetic chemistry. Important oxidation reactions include the transformation of alkenes to epoxides and diols, oxidation of sulfides to sulfoxides, and alcohols to either the corresponding carbonyl compounds or carboxylic acids. Transition metal complexes play an important role in the selective oxidation. Environmental concerns and regulations have increased in the public, political, and economical world over the last decade as quality of life is strongly connected to a clean environment. The present introductory chapter is not intended to give a complete survey of all published work on oxidation catalysis but rather to give a background and summary of recent important developments in catalytic oxidation reactions. Included is detail literature review on synthetic aspect of mononuclear Mo complexes and catalysis of various reactions such as oxidation of alkenes, amines and sulfide and further objective of thesis. Catalysis Division, National Chemical Laboratory, Pune 2 Chapter-1 Introduction 1.1 Introduction Chemistry is usually described as the science of matter and its changes at the atomic and molecular levels. It therefore deals primarily with collections of atoms, such as gases, molecules, crystals, and metals; describing, both the composition and statistical properties of such structures, as well as their transformations and interactions to become materials encountered in everyday life. This scientific subject also seeks to understand the properties and interactions of individual atoms, with the purpose of applying that knowledge to macroscopic levels [1]. Chemistry is rightfully described as a central science as it links together other sciences such as material science, nanotechnology, biology, pharmacology and geology. The application of chemistry can be traced back to early human activities such as the use of fire to prepare food, salt to preserve food, use of pigments in cave paintings and dyes to create beautiful clothing. ne of the biggest challenges in chemistry is discovering new chemical reactions that will enable society to function in a sustainable manner. Atom economy and waste minimization are at the heart of industrial policy, driven both by governmental incentives and by market considerations [2]. This complicated problem was addressed by various groups and is continuously tried to be solved using novel methodologies, such as catalysis. 1.2 Catalysis The word catalysis came from two Greek words, the prefix, cata meaning down, and the verb lysein meaning to split or break. Catalysis is a widely occurring process in nature. Enzymes catalyze numerous biological transformations and involve complex and large molecular weight structures that are evolved in nature over millions of years to carry out particular reactions very selectively. Man-made catalysts are relatively simple. Historically important examples are the production of H 2 S 4 using V 2 5 and the production of ammonia using iron-based catalysts. Research on the mode of operation and the synthesis of catalysts, including an improved understanding of thermodynamics due to the pioneering works of stwald and Van t Hoff, paved the way for a rational approach in developing more sophisticated and superior catalysts [3]. Catalysis Division, National Chemical Laboratory, Pune 3 Chapter-1 Introduction The term catalysis was coined by Berzelius around 1850 after observing changes in substances when they come in contact with small amount of species called ferments. Many years later in 1895 stwald came up with a definition A catalyst is a substance that changes the rate of a chemical reaction without itself appearing into the products according to which a catalyst could also slow down a reaction. Now a days, the definition in use is A catalyst is a substance which increases the rate at which a chemical reaction approaches equilibrium without becoming itself permanently involved. The effect of the catalyst is purely kinetic; catalysts work by providing an alternative mechanism that involves a different transition state at lower activation energy (Figure 1.1). Figure 1.1: Effect of the catalysts on a thermodynamically favorable reaction The basic principle of all catalysts is that they lower the activation energy by offering an alternative reaction path [4]. A catalyst decreases the activation energy of a reaction (ΔG is lowered), thereby increasing the rate of the reaction, but has no effect on the chemical equilibrium of the reaction (ΔG remains the same). The action of a catalyst can be very specific, which under ideal conditions, results in selective formation of the desired product and avoids side reactions. Further advantages of the use of catalytic reagents are reduced time and energy requirements, which results in an overall process with increased environmental sustainability. A catalyst can be poisoned when another Catalysis Division, National Chemical Laboratory, Pune 4 Chapter-1 Introduction compound binds to it irreversibly or chemically alters it. This effectively destroys the usefulness of the catalyst. Catalysis plays a key role in production of such a wide variety of products, which are having applications in food, clothing, drugs, plastics, agrochemicals, detergents, fuels etc. [5]. In addition to these, it plays an ever-expanding role in the balance of ecology and environment by providing cleaner alternative routes for stoichiometric technologies [6], by conversion of polluting emissions to harmless streams. Thus the importance of catalysis to society is obviously based on its great economic impact in the production of broad range of commodity products that improve our standard of living and quality of life. Usually, catalysts are categorized depending on the physical form in which they are used. There are mainly three types of catalysis processes: biocatalysis, homogeneous catalysis, and heterogeneous catalysis. In biocatalysis the catalyst is a biologically active molecule like enzyme. In homogeneous catalysis the catalyst is a transition metal with various ligand, which is in the same phase as that of the reactant and product whereas in heterogeneous catalysis the catalyst is a metal supported on various inorganic supports, which form a separate phase from reactant and product. Table 1.1 highlights major advantages of both homogeneous and heterogeneous catalytic processes. Table 1.1. Advantages of homogeneous and heterogeneous catalytic processes Homogeneous High and controllable chemo-, regio-, and enantio-selectivity High activity in terms of TN and TF Excellent accessibility of catalytic sites, no mass transfer limitations, no pressure drop Use of complex ligand systems to modify the catalyst Excellent catalyst description, mechanistic understanding Heterogeneous Easy separation of the catalyst from the product Excellent reuse of the catalyst (high total TN) Continuous operation frequently applied Resistance to drastic operational conditions Choice of a large variety of supports, e.g. silica, alumina, zeolites, carbon etc. Catalysis Division, National Chemical Laboratory, Pune 5 Chapter-1 Introduction Many homogeneous catalysts contain a metal ion that is surrounded by a ligand system, which stabilizes it in a certain oxidation state and offers coordination sites for substrates and reagents. By ingenious designing of ligands, more active and selective catalysts can be obtained. Transition metal catalysts are the largest class of homogeneous catalysts available to the synthetic chemist. In heterogeneous processes, the catalytic sites are part of an insoluble inorganic solid or are distributed on the surface of an insoluble support like silica, alumina or carbon. ne of the limiting factors of the catalytic activity of heterogeneous catalysts is the number of active sites, i.e. the surface area of the bulk material or of the supported species. Without surrounding organic ligands, it can be difficult to achieve high product selectivity; moreover, achieving enantioselectivity is generally difficult. n the other hand the big advantage of this kind of process is the easy separation of the catalyst from the reaction mixture. This allows easy purification of the product and facile reuse of the catalytic material. Hence, most of the industrial catalysts are heterogeneous in nature. In spite of this, there are a lot of important industrial processes based on homogeneous catalysis [7]. It is estimated that 85% of all chemical processes are run catalytically, with a ratio of applications of heterogeneous to homogeneous catalysis of approximately 3:1 [8]. In general, the advantages of the two systems are complementary to each other. The Nobel prizes [9] awarded in 2001 to Sharpless, Noyori and Knowles for their discovery of chirally catalysed oxidation and hydrogenation reactions, and in 2005 to Chauvin, Grubbs, and Schrock for their discovery of metathesis catalysts exemplify how a new catalyst can cause a paradigm shift in the chemical industry. However, the basic concept used for exploring the catalyst in homogeneous catalysis has not changed the catalyst productivity, defined as turnover number (TN), i.e. the number of moles of product produced per mole of catalyst. This number determines the catalyst costs. If a catalyst can be re-used, its productivity increases. The catalyst activity, often defined as turnover frequency (TF), i.e. how many moles of product one mole of the catalyst produces per unit time, determines the production capacity of a given catalyst. Catalysis Division, National Chemical Laboratory, Pune 6 Chapter-1 Introduction 1.3 rganometallic chemistry and homogeneous catalysis rganometallic compounds are defined as materials, which possess direct, more or less polar bonds between metal and carbon atoms [10]. Since Zeise synthesized in 1827 the first organometallic compound, K[PtCl 3 (CH 2 =CH 2 )], the organometallic chemistry has grown enormously although most of its applications have only been developed in recent decades. Some of the key points in the fast expansion of organometallic chemistry are the selectivity of organometallic complexes in organic synthesis (discovered with Grignard reagents at the end of the 19 th century) [11], and the interesting role that metals play in biological systems (e.g. enzymes, hemoglobin, etc.) [12]. ne of the important aspect of organometallic compounds is that they can be used as homogeneous catalysts in processes where all the reacting partners are present in one phase, usually the liquid [13]. Transition metal complexes act in different ways within the catalytic reaction: they bring the substrates together, activate the substrates by coordinating to the metal and lower the activation energy of the transition state. In general the use of a homogeneous catalyst in a reaction provides a new pathway, because the reactants interact with the metallic complex. These interactions make it possible for thermodynamically favored reactions, which need long times to reach equilibrium, to be accomplished within hours. Therefore, homogeneous catalysts can be used to synthesize compounds, which can hardly be obtained by conventional methods. The success of organometallic catalysts lies in the easy modification of their environment by ligand exchange. A very large number of different types of ligands can coordinate to transition metal ions. nce the ligands are coordinated, the reactivity of the metals may change dramatically. In fact the rate and selectivity of a given process can be optimized to the desired level by controlling the li
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