Examples of Oxidative Addition and Reductive Elimination Used in Industry

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Late Transition Metal Catalysis: examples of oxidative addition and reductive elimination used in industry 1. Alkene Hydrogenation many proceed by ox. addn / red. elim (see below) but radical - + and heterolytic H2 transfer (H and H sequentially) also known Wilkinson’s catalyst (next page) . selective for C=C over C=O and CN . does not scramble H and D . exclusively syn H2 addition (see eg. below) . commercially available 2. Hydroformylation (Oxo process) O R + H2 + CO R H synthesis gas 3. Monsanto Acetic Acid Process (carbonylation of MeOH) main use of acetic acid is in the synthesis of vinyl acetate, cellulose acetate, pharmaceuticals, dyes and pesticides. Acetic acid for food purposes is made by biocatalysis. the Monsanto process dominates the market but older methods such as Wacker chemistry (oxidation of ethylene via acetaldehyde – see section 5) are still practiced. conditions: 180 C / 30-40 atm / 10-3 M catalyst 4. Pd catalyzed cross couplings (2010 Nobel Prize) general mechanism is the same for many of the variants; they simply differ in the transmetallation reagent General mechanism: Pd2+ or Pd0 precatalyst concerted (sp2) or stepwise (sp3) R'X OA PdL2(solv) - solvent R'-R L R' Pd L X RE Isomerize L R' solvent Pd X L E-R L R' L R' Pd Pd L R R L Transmetallation Isomerize E-X Meet the family… Reaction E R’ type R type Promoter ! n 2 Stille SnBu 3 wide range sp>sp >aryl CuI, LiCl 3 >allylic>sp 2 2 - Hiyama SiR”3 sp , aryl sp , aryl F (required) $ 2 2 Suzuki B(OH)2 sp , aryl sp , aryl, base alkyl alkyl NaOH or Cs2CO3 Kumada MgX various various Negishi $ ZnX various various Sonogashira* Cu sp2>aryl CCR CuI, base e- poor>e- rich e- rich>e- poor (* without Pd this is the Stephens-Castro) $ awarded 2010 Nobel Prize in Chemistry (along with Heck) ! deceased 1989 in UA 232 crash in Sioux City, Iowa (http://www.youtube.com/watch?v=OAiYkX-Woh0) .

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4 Experimental
Chapter 1 Introduction Introduction Chapter 1 1.1 Transition Metal Complexes as Homogeneous Catalysts A variety of transition metals and metal complexes act as catalysts for organic reactions. The use of transition metal complexes to catalyse organic reactions is one of the most important applications of organometallic chemistry and has been the driving force in the rapid development of this field since catalysts are crucial to the turnover and selectivity in many chemical syntheses.1* Organometallic complexes catalyse a wide range of reactions, both in nature and in industry. For example, the naturally occurring metalloenzymes are vital catalysts in many metabolic processes such as respiration and are crucial in the photosynthetic cycle. Transition metal catalysts are used industrially in the production of bulk materials, pharmaceuticals, agrochemicals, flavours and fragrances2 by technological application such as; the hydroformylation of alkenes, the oxidation of alkenes, hydrocyanation of butadiene, and hydrogenation (Scheme 1.1).3 Hydroformylation of Alkenes (Oxo Process) O O H C Co(I) or Rh(I) C R + H2 +CO R H + R * Oxidation of alkenes (Wacker Process) O Pd(II) + Cu(II) + 1 O H 2 2 Hydrocyanation of Butadiene Ni(0) CN + 2HCN NC Hydrogenation (Wilkinson’s Catalyst) [RhCl(PPh3)3] R + H2 R Scheme 0.1 * References begin on page 16. 1 Introduction Chapter 1 One of the most important examples of homogeneous catalysis is the carbonylation of methanol to produce acetic acid, in what is known as the Monsanto Process (Scheme 1.2). Acetic acid is used for different purposes in the industry such as producing vinegar, food preservatives, solvents and plastics.
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Bimetallic Catalyst Catalyzed Carbonylation of Methanol to Acetic Acid
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Oxidative Addition & Reductive Elimination
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Oxidative Addition of Polar Reagents
OXIDATIVE ADDITION OF POLAR REAGENTS Organometallic chemistry has vastly expanded the practicing organic chemist’s notion of what makes a good nucleophile or electrophile. Pre-cross-coupling, for example, using unactivated aryl halides as electrophiles was largely a pipe dream (or possible only under certain specific circumstances). Enter the oxidative addition of polarized bonds: all of a sudden, compounds like bromobenzene started looking a lot more attractive as starting materials. Cross-coupling reactionsinvolving sp2- and sp-hybridized C–X bonds beautifully complement the “classical” substitution reactions at sp3electrophilic carbons. Oxidative addition of the C–X bond is the step that kicks off the magic of these methods. In this post, we’ll explore the mechanisms and favorability trends of oxidative additions of polar reagents. The landscape of mechanistic possibilities for polarized bonds is much more rich than in the non-polar case—concerted, ionic, and radical mechanisms have all been observed. Concerted Mechanisms 2 Oxidative additions of aryl and alkenyl Csp –X bonds, where X is a halogen or sulfonate, proceed through concertedmechanisms analogous to oxidative additions of dihydrogen. Reactions of N–H and O–H bonds in amines, alcohols, and water also appear to be concerted. A π complex involving η2-coordination is an intermediate in the mechanism of insertion into aryl halides at least, and probably vinyl halides too. As two open coordination sites are necessary for concerted oxidative addition, loss of a ligand from a saturated metal complex commonly precedes the actual oxidative addition event. Concerted oxidative addition of aryl halides and sulfonates. Trends in the reactivity of alkyl and aryl (pseudo)halides toward oxidative addition are some of the most famous in organometallic chemistry.
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18- Electron Rule. 18 Electron Rule Cont’D Recall That for MAIN GROUP Elements the Octet Rule Is Used to Predict the Formulae of Covalent Compounds
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Some Problems in the Oxidative Addition and Binding of an Ethylene to a Transition-Metal Center
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