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Chapter 2 Ligands used for aqueous organometallic catalysis Solubility of the catalysts in water is determined by their overall hydrophilic nature which may arise either as a consequence of the charge of the complex ion as a whole, or may be due to the good solubility of the ligands. Although transition metal complexes with small ionic ligands, such as halides, pseudohalides or simple carboxylates can be useful for specific reactions the possibility of the variation of such ligands is very limited. As in organometallic catalysis in general, phosphines play a leading role in aqueous organometallic catalysis (AOC), too. There is a vast armoury of synthetic organic chemistry available for preparation and modification of various phosphine derivatives of which almost exclusively the tertiary phosphines are used for catalysis. The main reason for the ubiquity of tertiary phosphines in catalysis is in that most transformations in AOC involve the catalysts in a lower valent state at one or more stages along the catalytic cycle and phosphines are capable of stabilizing such low oxidation state ions, such way hindering metal precipitation. For the same reason, ligands posessing only hard donor atoms (e.g. N or O) are not common in AOC and used mainly for synthesizing catalysts for oxidations or other reactions where the oxidation state of the metal ion remains constant throughout the catalytic cycle (examples can be the heterolytic activation of dihydrogen or certain hydrogen transfer reactions). Some of the neutral (that is non-ionic) ligands are water-soluble due to their ability of forming several strong hydrogen bonds to the surrounding water molecules. These ligands usually contain several N or O atoms, such as the l,3,5-triaza-7-phosphaadamantane (PTA, the phosphorus analog of urotropin), tris(hydroxymethyl)phosphine, or several phosphines containing long polyether (e.g. polyethyleneglycol-, PEG-type) chains. Most of the ligands in AOC, however, are derived from water- insoluble tertiary phosphines by attaching onto them ionic or polar groups, 11 12 Chapter 2 namely sulfonate, sulfate, phosphonate, carboxylate, phenolate, quaternary ammonium and phosphonium, hydroxylic, polyether, or polyamide (peptide) etc. substituents or a combination of those. This latter approach stems from the philosophy behind research into AOC in the early days when the aim was to “transfer” efficient catalytic processes, like hydroformylation, from the homogeneous organic phase into an aqueous/organic biphasic system simply by rendering the catalyst water soluble through proper modification (e.g. sulfonation) of its ligands. Although this approach is still useful, so much more is known today of the specific characteristics and requirements of the processes in AOC that tayloring the ligands (and by this way the catalysts) to the particular chemical transformation in aqueous or biphasic systems is not only a more and more manageable task but a drive at the same time for synthesis of new compounds for specific use in aqueous environment. In the following few sections we shall now review the most important water-soluble ligands and the synthetic methods of general importance. It should be noted, that in many cases only a few examples of the numerous products available through a certain synthetic procedure are shown in the tables and the reader is referred to the literature for further details. 2.1 TERTIARY PHOSPHINE LIGANDS WITH SULFONATE OR ALKYLENE SULFATE SUBSTITUENTS This class of compounds is comprised by far the most important ligands in aqueous organometallic chemistry. The main reasons for that are the following: sulfonated phosphines are generally well soluble in the entire World Energy Use World Energy Use Bởi: OpenStaxCollege Energy is an important ingredient in all phases of society We live in a very interdependent world, and access to adequate and reliable energy resources is crucial for economic growth and for maintaining the quality of our lives But current levels of energy consumption and production are not sustainable About 40% of the world’s energy comes from oil, and much of that goes to transportation uses Oil prices are dependent as much upon new (or foreseen) discoveries as they are upon political events and situations around the world The U.S., with 4.5% of the world’s population, consumes 24% of the world’s oil production per year; 66% of that oil is imported! Renewable and Nonrenewable Energy Sources The principal energy resources used in the world are shown in [link] The fuel mix has changed over the years but now is dominated by oil, although natural gas and solar contributions are increasing Renewable forms of energy are those sources that cannot be used up, such as water, wind, solar, and biomass About 85% of our energy comes from nonrenewable fossil fuels—oil, natural gas, coal The likelihood of a link between global warming and fossil fuel use, with its production of carbon dioxide through combustion, has made, in the eyes of many scientists, a shift to non-fossil fuels of utmost importance—but it will not be easy World energy consumption by source, in billions of kilowatt-hours: 2006 (credit: KVDP) 1/8 World Energy Use The World’s Growing Energy Needs World energy consumption continues to rise, especially in the developing countries (See [link].) Global demand for energy has tripled in the past 50 years and might triple again in the next 30 years While much of this growth will come from the rapidly booming economies of China and India, many of the developed countries, especially those in Europe, are hoping to meet their energy needs by expanding the use of renewable sources Although presently only a small percentage, renewable energy is growing very fast, especially wind energy For example, Germany plans to meet 20% of its electricity and 10% of its overall energy needs with renewable resources by the year 2020 (See [link].) Energy is a key constraint in the rapid economic growth of China and India In 2003, China surpassed Japan as the world’s second largest consumer of oil However, over 1/3 of this is imported Unlike most Western countries, coal dominates the commercial energy resources of China, accounting for 2/3 of its energy consumption In 2009 China surpassed the United States as the largest generator of CO2 In India, the main energy resources are biomass (wood and dung) and coal Half of India’s oil is imported About 70% of India’s electricity is generated by highly polluting coal Yet there are sizeable strides being made in renewable energy India has a rapidly growing wind energy base, and it has the largest solar cooking program in the world Past and projected world energy use (source: Based on data from U.S Energy Information Administration, 2011) 2/8 World Energy Use Solar cell arrays at a power plant in Steindorf, Germany (credit: Michael Betke, Flickr) [link] displays the 2006 commercial energy mix by country for some of the prime energy users in the world While non-renewable sources dominate, some countries get a sizeable percentage of their electricity from renewable resources For example, about 67% of New Zealand’s electricity demand is met by hydroelectric Only 10% of the U.S electricity is generated by renewable resources, primarily hydroelectric It is difficult to determine total contributions of renewable energy in some countries with a large rural population, so these percentages in this table are left blank Energy Consumption—Selected Countries (2006) Country Consumption, Oil in EJ (1018 J) Energy Electricity Use Natural Other Use per per Coal Nuclear Hydro Gas Renewables capita capita (kWh/yr) (GJ/ yr) Australia 5.4 34% 17% 44% 0% 3% 1% 10000 260 Brazil 9.6 48% 7% 5% 35% 2% 2000 50 China 63 22% 3% 69% 1% 6% 1500 35 Egypt 2.4 50% 41% 1% 6% 990 32 Germany 16 37% 24% 24% 11% 1% 6400 173 India 34% 7% 52% 1% 5% 470 13 Indonesia 4.9 51% 26% 16% 0% 2% 3% 420 22 Japan 24 48% 14% 21% 12% 4% 1% 7100 176 New Zealand 0.44 32% 26% 6% 11% 19% 8500 102 Russia 31 19% 53% 16% 5% 6% 5700 202 U.S 105 40% 23% 22% 8% 3% 1% 12500 340 World 432 39% 23% 24% 6% 6% 2% 2600 71 15 1% 0% 0% 3% Energy and Economic Well-being The last two columns in this table examine the energy and electricity use per capita Economic well-being is dependent upon energy use, and in most countries higher standards of living, as measured by GDP (gross domestic product) per capita, are 3/8 World Energy Use matched by higher levels of energy consumption per capita This is borne out in [link] Increased efficiency of energy use will change this dependency A global problem is balancing energy resource development against the harmful effects upon the environment in its extraction and ... HƯỚNG DẪN CÀI ĐẶT,TẠO USER VÀ SỬ DỤNG CHƯƠNG TRÌNH SKYPE  HƯỚNG DẪN CÀI ĐẶT, TẠO USER VÀ SỬ DỤNG CHƯƠNG TRÌNH SKYPE. 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These chapters will change before the book is published. Download all of the book's code here. Chapter P: Preface There’s no doubt that the Web was a catalyst for a revolution that changed the lives of software developers and end users alike. Web services provide the foundation for another profound revolution in the way we build and use applications. It is up to developers like you and I to take this foundation and make the revolution happen. With this book, I aim to give you the information and insight you need to design and build next generation distributed interoperable applications with Web services. Chapter 1: Introduction to Web Services You've probably heard about Web services and may have read about them. It seems like every trade publication, book, and Web site has some mention of Web services. Unfortunately, most of the current coverage of Web services does not clearly explain what they are really all about, they just trumpet how wonderful Web services are, which comes across as hype. In this chapter I focus on two things: Explaining what Web services are really all about and showing you scenarios where you would use Web services and scenarios where you really should not use them. Chapter 2: XSD: The Web Services Type System Web services are all about data exchange between heterogenous applications. This data exchange cannot be accomplished without a common, agreed upon type system that provides standard types as well as the ability to define your own types. This chapter is designed to first get you up and running with XSD, the Web services type system, then show you how XSD is used to specify message formats and validate data exchanged between client and service. This is not intended as a rigorous explanation of XSD – that would require an entire book. Rather, this chapter explains those aspects of XSD that are commonly used in Web services. Chapter 3: SOAP: Invoking Web Services In chapter 1 you learned how to invoke a Web service using the SOAP Toolkit and .NET. In this chapter you will learn how these and other tools use SOAP messages to invoke Web services. I will explain the goals and architecture of SOAP and the ways it can be used including messaging and RPC. This chapter’ s objective is to teach you what SOAP is capable of doing and how, so that you get a better understanding of the tools you’ll be using such as .NET and the SOAP Toolkit. Such understanding will come in handy when you need to invoke a Web service and you find the tools have limitations that prevent from using them. This and the next chapter are tightly integrated and together complete the picture of how Web services work. Chapter 4: WSDL: Describing Web Services Just as XML Schemas are used to describe the data types exposed by Web services, there is a need for a language that can be used to describe the complete interfaces exposed by Web services. In this chapter I explain the concepts and terminology behind the most commonly used language for describing Web service interfaces, the Web Services Description Language. I will show you how to write WSDL documents that describe your Web service’s interface and how to read WSDL documents for services that you want to invoke. The goal of this chapter is to teach you to World Wide Web World Wide Web Bởi: Lê Văn Tâm World .. .World Energy Use The World s Growing Energy Needs World energy consumption continues to rise, especially in the developing countries (See [link].) Global demand for energy has tripled... renewable energy India has a rapidly growing wind energy base, and it has the largest solar cooking program in the world Past and projected world energy use (source: Based on data from U.S Energy. .. dependent upon energy use, and in most countries higher standards of living, as measured by GDP (gross domestic product) per capita, are 3/8 World Energy Use matched by higher levels of energy consumption