Osmium complexes, oxidative-addition reactions

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). 

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. 

Osmium, quinuclidinetetraoxime-stereochemistry, 44 Osmium, tetrachloronitrido-tetraphenylarsenate stereochemistry, 44 Osmium, tris( 1,10-phenanthroline) -structure, 64 Osmium(II) complexes polymerization electrochemistry, 488 Osmium(III) complexes magnetic behavior, 273 Osmium(lV) complexes magnetic behavior, 272 Osmium(V) complexes magnetic behavior, 272 Osmium(VI) complexes magnetic behavior, 272 Oxaloacetic acid decarboxylation metal complexes, 427 Oxamidoxime in gravimetry, 533 Oxidation-reduction potentials non-aqueous solvents, 27 Oxidation state nomenclature, 120 Oxidative addition reactions, 282 Oxidative dehydrogenation coordinated imines, 455 Oximes... 

Unlike the above example, the majority of five-coordinate complexes appear to undergo oxidative-addition reactions in two separate steps. Additions to the bis phosphine complexes of ruthenium(O) (36) and osmium(O) (39) (XIV) are the most thoroughly studied examples of this generalization (see Section IV). The configurations of these complexes have been established by infrared spectroscopy and, in the case of the osmium complex, by X-ray diffraction (72), Addition of an electrophile A" " (for example H+, HgX+, or Br+ from Br2) to the five-coordinate complexes... 

Figure 5.2. Synthetic pathway for producing Os(CS)(CO)2(PPh3)3, a zerovaient osmium thiocarbonyl complex intended for use in novel oxidative addition reactions.

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... 

The very sensitive ether peroxide test strips (Merckoquant, Art. No. 10011), available from E. Merck, Darmstadt, are used. If the test is still positive at this point, an additional 0.2 ml. of N-methyl morpholine is added. Stirring and heating at 75° are continued for another 5 hours. Remaining peroxide renders the work-up and drying of the product potentially hazardous. N-Methylmorpholine N-oxide (1) and hydrogen peroxide form a strong 1 1 complex. In the reaction with osmium tetroxide, this complex produces conditions similar to those of the Milas reaction,7 and some ketol formation may result. 

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... 

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... 

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... 

Oxidative addition to ruthenium and osmium four-coordinate complexes occurs readily. These complexes are excellent starting materials for group VIII complexes. Addition of formaldehyde to complexes M(CO)L(PPh3)2 (L = CO or PPhs selection of L is metal dependent) leads to oxidative addition products, a reaction of relevance to Fischer-Tropsch processes. The ruthenium complex is proposed as an intermediate only the osmium complex has been isolated ... 

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