Catalyzed by Transition Metals

The transformation of alkenes in the presence of Group VUI metal catalysts affords carboxylic acids or carboxylic acid derivatives depending on the protic reagent used 10 14-16 23 7-123 

A similar addition to alkynes results in the formation of the corresponding unsaturated acids and derivatives.14,23,121-124 Cobalt, nickel, and iron carbonyls, as well as palladium complexes, are the most often used catalysts.14 

The syntheses of carboxylic acids and esters are widely studied processes. Since the first examples of carboxylation in the presence of metal carbonyls were reported by Reppe, these reactions are sometimes referred to as the Reppe reactions. In his pioneering work125-127 stoichiometric or catalytic amounts of [Ni(CO)4] and ethylene or acetylene were reacted in the presence of water or alcohols to form saturated and unsaturated acids and esters. Commercial processes are practiced in the manufacture of propionic acid, acrylic acid and acrylates (see Section 7.2.4). 

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A large number of organometallic compounds are based on transition metals Examples include organic derivatives of iron nickel chromium platinum and rhodium Many important industrial processes are catalyzed by transition metals or their complexes Before we look at these processes a few words about the structures of transition metal complexes are m order... 

Transition-metal-catalyzed oxidations may or may not proceed via peroxocomplexes. Twelve important industrial organic oxidation processes catalyzed by transition metals, many of which probably involve peroxo intermediates, have been tabulated (88). Even when peroxo intermediates can be isolated from such systems, it does not necessarily foUow that these are tme intermediates in the main reaction. 

Peroxyesters decompose by an electron-transfer process catalyzed by transition metals (44,168,213) (eq. 34). This reaction has been used synthetically to bond an acyloxy group to appropriate coreactive substrates (eq. 35). 

Magnesium reacts slowly at lower temperatures to give the amide, as do all active metals this reaction is catalyzed by transition metal ions. Aluminum nitride [24304-00-5] AIN, barium nitride [12047-79-9] Ba2N2, calcium nitride [12013-82-0] Ca2N2, strontium nitride [12033-82-8], Sr2N2, and titanium nitride [25583-20-4], TiN, may be formed by heating the corresponding amides. 

Coupling of butadiene with CO2 under electrochemically reducing conditions produces decadienedioic acid, and pentenoic acid, as weU as hexenedioic acid (192). A review article on diene telomerization reactions catalyzed by transition metal catalysts has been pubUshed (193). 

Elemental Huonne as a Legitimate Reagent for Selective Fluonnation of Orgamc Compounds Fluoroaromatic Compounds Synthesis, Reactions, and Commercial Applications New Aspects of Carbonylations Catalyzed by Transition Metal Complexes Polyfluoroaromatics An Excursion m Carbamon Chemistry ... 

Direct carbonylation of heterocycles at C—H bond catalyzed by transition metal complexes 98YGK443. 

Synthesis of N-heterocycles with C—N bond formation catalyzed by transition metal catalysts 97SL749. 

Total syntheses of pyrrole alkaloids, furanoterpenes, macrolide antibiotics, and carbohydrates based on transformations catalyzed by transition metals 99SL1523. 

In some cases the rearrangement can be catalyzed by transition metal compounds, and thus caused to take place at room temperature. The ordinary, uncatalyzed rearrangement requires temperatures in the range of 150-250 °C. 

The hydrosilation of conjugated dienes is catalyzed by transition metal complexes34, and has been developed into a useful asymmetric synthesis of allylsilanes35,36. 

The Metathesis of Unsaturated Hydrocarbons Catalyzed by Transition Metal Compounds... 

The addition of halocarbons (RX) across alkene double bonds in a radical chain process, the Kharasch reaction (Scheme 9.29),261 has been known to organic chemistry since 1932. The overall process can be catalyzed by transition metal complexes (Mt"-X) it is then called Atom Transfer Radical Addition (ATRA) (Scheme 9.30).262... 

Figure 4.5 Simplified mechanism of the racemization of sec-alcohols catalyzed by transition metal complexes.

The racemization mechanism of sec-alcohols has been widely studied [16,17]. Metal complexes of the main groups of the periodic table react through a direct transfer of hydrogen (concerted process), such as aluminum complexes in Meerwein-Ponn-dorf-Verley-Oppenauer reaction. However, racemization catalyzed by transition metal complexes occurs via hydrogen transfer processes through metal hydrides or metal dihydrides intermediates (Figure 4.5) [18]. 

Deronzier A, Moutet J-C. 2003. Electrochemical reactions catalyzed by transition metal complexes. In Ward MD, editor. Comprehensive Coordination Chemistry, II. Volume 9. Amsterdam Elsevier, p. 471. 

Catecholborane and pinacolborane are especially useful in hydroborations catalyzed by transition metals.163 Wilkinson s catalyst Rh(PPh3)3Cl is among those used frequently.164 The general mechanism for catalysis is believed to be similar to that for homogeneous hydrogenation and involves oxidative addition of the borane to the metal, generating a metal hydride.165... 

Lewis acids catalyze the reaction of alkylzinc reagents with acyl chlorides.160 The reaction is also catalyzed by transition metals, as is discussed in Chapter 8. 

Ring opening polymerization can also be catalyzed by transition metals as shown in reaction (13) (12,30). The process appears to involve hydrogenolysis of the Si-N bond, given that reaction (13)... 

Hydrolysis of oximes catalyzed by transition-metal complexes has not been studied prior to a report by Kostic et al. They have reported kinetics of hydrolysis of acetoxime to acetone catalyzed by two palladium(II) complexes, identified active species in the hydrolysis reaction, proposed a reaction mechanism, and fully characterized a bis(acetoxime) complex that is relatively stable toward hydrolysis.458... 

Ojima, I. Zhang, Z. Korda, A. Ingallina, P. Clos, N. New Carbonylations Catalyzed by Transition Metal Complexes, In Advances in Chemistry Series 230 American Chemical Society, Washington, DC, 1992, 277-296. 

Electrochemical Reactions Catalyzed by Transition Metal Complexes... 

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