Osmium oxidative addition

The formation of the first osmium hydrido(alkoxo) complex, a yellow air-stable and thermally stable hydrido(methoxo)osmium(II) complex, trans-[OsH(OMe)(Cl) (NO) (P Pr3)2] (72), by the oxidative addition of MeOH to a 16-electron complex, trans-[OsCl(NO)(P Pr3)2] (71) was briefly reported (Eq. 6.22) [51]. 

Using as catalyst precursors the clusters Os3H2(CO)i0 and Os3(CO)12 [71, 72], Laine and coworkers found a deuteration pattern of quinoline hydrogenation similar to that shown in Scheme 16.16, except for the presence of more deuterium in the 4-position and less in the 2-position, which has been interpreted in terms of the occurrence of oxidative addition of the osmium cluster to C-H bonds in quinoline, and also 1,4-hydrogenation (Scheme 16.17). 

Chloroxytrifluoromethane, 26 137-139 reactions, 26 140-143 addition to alkenes, 26 145-146 oxidative addition, 26 141-145 vibrational spectra, 26 139 Chloryl cation, 18 356-359 internal force constants of, 18 359 molecular structure of, 18 358, 359 properties of, 18 357, 358 synthesis of, 18 357, 358 vibrational spectra of, 18 358, 359 Chloryl compounds, reactions of, 5 61 Chloryl fluoride, 18 347-356 chemical properties of, 18 353-356 fluoride complexes of, 5 59 molecular structure of, 18 349-352 physical properties of, 18 352, 353 preparation, 5 55-57 and reactions, 27 176 properties of, 5 48 reactions, 5 58-61, 18 356 synthesis of, 18 347-349 thermal decomposition of, 18 354, 355 vapor pressures, 5 57, 18 353 vibrational spectra of, 18 349-352 Chloryl ion, 9 277 Cholegobin, 46 529 Cholesterol, astatination, 31 7 Cholorofluorphosphine, 13 378-380 h CHjPRj complexes, osmium, 37 274 Chromatium, HiPIP sequence, 38 249 Chromatium vinosum HiPIP, 38 108, 133 Fe4S4 + core, 33 60 Chromato complexes, osmium, 37 287... 

In many cases the reaction of osmium carbonyls and acetylenes does not stop at the first stages as in [56], [57], or [57]. Instead, two or more acetylene molecules are incorporated, and in some cases acetylene trimerization to benzenes takes place (182, 371, 379). Incorporation of two acetylene molecules can lead to metallacyclo-pentadiene clusters like [55] (126,168,171,182,184, 223, 371), or to metallacyclo-hexadienone clusters hke [59] (126, 223). And the complex [90], another intermediate, is related to [55] by an intramolecular oxidative addition reaction (168,169). 

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

Further chemistry of alkenes and alkynes is described in this chapter, with emphasis on addition reactions that lead to reduction and oxidation of carbon-carbon multiple bonds. First we explain what is meant by the terms reduction and oxidation as applied to carbon compounds. Then we emphasize hydrogenation, which is reduction through addition of hydrogen, and oxidative addition reactions with reagents such as ozone, peroxides, permanganate, and osmium tetroxide. We conclude with a section on the special nature of 1-alkynes— their acidic behavior and how the conjugate bases of alkynes can be used in synthesis to form carbon-carbon bonds. 

The conversion of alkenes to 1,2-diols by osmium tetroxide is also an olefin addition reaction. In this case a hydroxy group is added to each carbon of the olefin group, and the addition is termed an oxidative addition since the diol product is at a higher oxidation level than the alkene reactant. Oxidation of the carbon atoms of the alkene takes place in the first step, which is the reaction with 0s04 to produce the intermediate osmate ester. 

Zinc serves to further reduce osmium and free the diol product. Similar oxidative additions to alkenes occur with bromine, chlorine, IN3, peracids, and many other electrophiles. 

Oxidative additions are frequently observed with transition metal d8 systems such as iron(0), osmium(O), cobalt(I), rhodium(I), iridium(I), nickel(II), palladium(II) and platinum(II). The reactivity of d8 systems towards oxidative addition increases from right to left in the periodic table and from top to down within a triad. The concerted mechanism is most important and resembles a concerted cycloaddition in organic chemistry (Scheme 1.1). The reactivity of metal complexes is influenced by their... 

The analogous bromo and iodo cations have been prepared by oxidative addition of halogen to bis(triphenylphosphine)osmium tricarbonyl (52). 

Reduction of alkyl osmium complex 160 with NaBH4 or NaBD4 gives the methyl hydrido and methyl deutero osmium complexes 169. Treatment of 169 with trityl cation gives the metallaheterocycle 170. This reaction probably occurs via cationic intermediates 171 and 172. The coordinatively unsaturated 172 then undergoes an intramolecular oxidative addition with... 

Osmium forms a wide variety of alkyl and aryl complexes including homoleptic alkyl and aryl complexes and many complexes with ancillary carbonyl (see Carbonyl Complexes of the Transition Metals), cyclopentadienyl (see Cyclopenta-dienyl), arene (see Arene Complexes), and alkene ligands (see Alkene Complexes). It forms stronger bonds to carbon and other ligands than do the lighter elements of the triad. Because of this, most reactions of alkyl and aryl osmium complexes are slower than the reactions of the corresponding ruthenium complexes. However, because osmium is more stable in higher oxidation states, the oxidative addition (see Oxidative Addition) of C-H bonds is favored for osmium complexes. The rate of oxidative addition reactions decreases in the order Os > Ru Fe. 

The oxidative addition of C H bonds of ligands is very common and this reaction forms metal alkyl or metal aryl complexes. In osmium triarylphosphine complexes, orthomet-allation gives four-membered metaUocycles. When the ortho... 

When bulky alkenes are used, addition of a second alkene molecule to produce an oxo-bis(l,2-diolato)osmate(VI) 7 is preferred. Subsequent osmium oxidation and hydrolysis releases the 1,2-diol and regenerates the trioxo(l,2-diolato)osmate(VIII) 4 that can reenter the catalytic cycle. In this latter case amine addition has no major effect. Proof for the existence of species of type 7 (X-ray) as well as for the catalytic properties of 4 have recently been provided38. 

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