Olefin complexes oxidations

High-valent ruthenium oxides (e. g., Ru04) are powerful oxidants and react readily with olefins, mostly resulting in cleavage of the double bond [132]. If reactions are performed with very short reaction times (0.5 min.) at 0 °C it is possible to control the reactivity better and thereby to obtain ds-diols. On the other hand, the use of less reactive, low-valent ruthenium complexes in combination with various terminal oxidants for the preparation of epoxides from simple olefins has been described [133]. In the more successful earlier cases, ruthenium porphyrins were used as catalysts, especially in combination with N-oxides as terminal oxidants [134, 135, 136]. Two examples are shown in Scheme 6.20, terminal olefins being oxidized in the presence of catalytic amounts of Ru-porphyrins 25 and 26 with the sterically hindered 2,6-dichloropyridine N-oxide (2,6-DCPNO) as oxidant. The use... 

Organoiron complexes (7) are converted in high yield into ammonium salts (8) these in turn undergo oxidatively induced ligand transfer and cyclization to give azetidinones (9) in moderate yields (Scheme 9). Formation of the trans product (9b) indicates a stereochemical sequence of trans addition to the olefin complex followed by carboxamidation with retention of configuration at the C—Fe bond. 

The effective atomic number rule (the 18-electron rule) was described briefly in Chapter 16, but we will consider it again here because it is so useful when discussing carbonyl and olefin complexes. The composition of stable binary metal carbonyls is largely predictable by the effective atomic number (EAN) rule, or the "18-electron rule" as it is also known. Stated in the simplest terms, the EAN rule predicts that a metal in the zero or other low oxidation state will gain electrons from a sufficient number of ligands so that the metal will achieve the electron configuration of the next noble gas. For the first-row transition metals, this means the krypton configuration with a total of 36 electrons. 

In most palladium-catalyzed oxidations of unsaturated hydrocarbons the reaction begins with a coordination of the double bond to palladium(II). In such palladium(II) olefin complexes (1), which are square planar d8 complexes, the double bond is activated towards further reactions, in particular towards nucleophilic attack. A fairly strong interaction between a vacant orbital on palladium and the filled --orbital on the alkene, together with only a weak interaction between a filled metal d-orbital and the olefin ji -orbital (back donation), leads to an electrophilic activation of the alkene9. 

In a different approach, Franck-Neumann et al. [24] utilized the manganese complex 14 (formed by deracemization) to obtain the enantiomerically pure target molecule 12 via Horner-Wadsworth-Emmons olefination and oxidative decomplexation of the intermediate vinylallene complex 15 (Scheme 18.6). 

Other possible mechanisms, corresponding to those discussed for the alkyne, have been considered. The oxidative addition pathway is excluded because all vinyl intermediates (see below) are found at high energy with respect to the n olefin complex. 

Examples of catalytic formation of C-C bonds from sp C-H bonds are even more scarce than from sp C-H bonds and, in general, are limited to C-H bonds adjacent to heteroatoms. A remarkable iridium-catalyzed example was reported by the group of Lin [116] the intermolecular oxidative coupling of methyl ethers with TBE to form olefin complexes in the presence of (P Pr3)2lrH5 (29). In their proposed mechanism, the reactive 14e species 38 undergoes oxidative addition of the methyl C-H bond in methyl ethers followed by olefin insertion to generate the intermediate 39. p-hydride elimination affords 35, which can isomerize to products 36 and 37 (Scheme 10). The reaction proceeds under mild condition (50°C) but suffers from poor selectivity as well as low yield (TON of 12 after 24 h). 

Palladium chloride or the chloropalladite ion catalyze the oxidation of olefins to aldehydes or ketones, presumably by forming unstable palladium-olefin complex intermediates 196). A reaction of great industrial importance is the palladium chloride/cupric chloride catalyzed oxidation of ethylene to acetaldehyde 195). The first stage is presumably the oxidative hydrolysis of ethylene,... 

When an appropriate chiral phosphine ligand and proper reaction conditions are chosen, high enantioselectivity is achieved. If a diphosphine ligand of C2 symmetry is used, two diastereomers of the enamide coordination complex can be produced because the olefin can interact with either the re face or the si face. This interaction leads to enantiomeric phenylalanine products via diastereomeric Rh(III) complexes. The initial substrate-Rh complex formation is reversible, but interconversion of the diastereomeric olefin complexes may occur by an intramolecular mechanism involving an olefin-dissociated, oxygen-coordinated species (18h). Under ordinary conditions, this step has higher activation enthalpies than the subsequent oxidative addition of H2, which is the first... 

Benzamido-cinnamic acid, 20, 38, 353 Benzofuran polymerization, 181 Benzoin condensation, 326 Benzomorphans, 37 Benzycinchoninium bromide, 334 Benzycinchoninium chloride, 334, 338 Bifiinctional catalysts, 328 Bifiinctional ketones, enantioselectivity, 66 BINAP allylation, 194 allylic alcohols, 46 axial chirality, 18 complex catalysts, 47 cyclic substrates, 115, 117 double hydrogenation, 72 Heck reaction, 191 hydrogen incorporation, 51 hydrogen shift, 100 hydrogenation, 18, 28, 57, 309 hydrosilylation, 126 inclusion complexes, oxides, 97 ligands, 19, 105 molecular structure, 50, 115 mono- and bis-complexes, 106 NMR spectra, 105 olefin isomerization, 96... 

This paper presents the results of an investigation of the oxidation of substituted olefins in the presence of hydrocarbon-soluble transition metal complexes. Results indicate that the initial interaction of oxygen with the olefin probably does not occur within the coordination sphere of the metal. The best interpretation appears to be autoxidation of the olefin, initiated either by the metal or by metal catalyzed decomposition of peroxidic impurities. The initial product of an olefin having allylic hydrogens is an allylic hydroperoxide species this is usually the case in radical initiated autoxidations. Nonetheless, with some metal complexes the product profile differs markedly from that observed when radical initiators are used. In the presence of several complexes, oxidation is... 

---