Osmium alkenyl

The molecular structure of this compound determined by X-ray diffraction analysis reveals a significant contribution of the resonance form b (Scheme 34) to the osmium alkenyl bond, which is improved by the presence of the carboxyl substituent.71... 

Decatrienes, in intramolecular Alder-ene reactions, 10, 578 Dechlorination reactions, via cobalt(III) complexes, 7, 44 Decomposition pathways mixed metal carbonyls, via sonochemistry, 1, 310 in mononuclear ruthenium and osmium alkenyl formations, 6, 405... 

The structure of the styryl derivative Os ( ,)-CH=CHPh Cl(CO)(PIPr3)2 has been determined by X-ray diffraction analysis.33 In agreement with OsHCl(CO) (P Pr3)2, the coordination polyhedron around the osmium atom can be rationalized as square-pyramidal with the phosphines, mutually tram disposed, the chloride and the carbonyl group occupying the basal sites, and the alkenyl located at the... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

Mononuclear osmium half-sandwiches, with rf-cyclopentadienyls and 7]5-indenyls alkenyls and allenyls with t/-M-C bonds, 6, 558 alkenyl vinylidenes, 6, 593 alkyl, aryl, acyl complexes, 6, 552 with alkylidyne complexes, 6, 599 alkynyl and enynyl complexes, 6, 567 allenylidene and cumulenylidene complexes,... 

An example is the acid-catalyzed condensation between the dimethyl acetal of an ot,/ -un-saturated aldehyde and a suitably AT-protected norephedrine which affords 2-alkenyloxazoli-dines 1 with a general kinetic as well as a thermodynamic preference for the diastereomer with the alkenyl moiety cis to the methyl and phenyl substituents1. Reaction with osmium tetroxide leads to the cw-diols 2 and 3 with a d.r. of 73 27. 

In contrast to the reaction with phenylacetylene, the treatment of 190 with 2 equiv of methyl propiolate leads to the alkenyl-alkynyl compound 200 (Scheme 55). The use of a 1 1 molar ratio of alkyne to osmium complex gives the same product along with unreacted dihydride-dihydrogen complex [79]. The addition of a toluene solution of HCl to a toluene solution of 200 produces the carbon-carbon coupling of the alkynyl and alkenyl fragments to give selectively the... 

The reactions collected in Schemes 56 and 57 contain overwhelming evidence proving that the direction of the addition to alkynyl and alkenyl acetate complexes of osmium and ruthenium is determined by the electronic nature of the metallic center (Os or Ru), by the electronic properties of the ancillary ligands of the complexes, and also by the source of the electrophile. 

Pandit and coworkers also prepared a functionahzed tricyclic core (148) by a different version of the intramolecular Diels-Alder reaction (Scheme 13). For further introduction of an alkenyl group, the trisubstituted alkene in 148 was subjected to osmium dihydroxylation followed by dehydration imder... 

It is interesting to note that the OsHCl(CO)(PR3)2 complexes catalyze the hydrogenation of styrene to ethylbenzene at faster rates than those for the alkyne reduction, suggesting that the origin of the selectivity is not kinetic. Thus, the stable alkenyl complexes represent a thermodynamic sink that causes virtually all the osmium in solution to be present as Os (E)-CH=CHPh Cl(CO)(PR3)2. Therefore, the kinetically unfavorable pathway becomes the only one available in the presence of alkyne. This thermodynamic difference is illustrated qualitatively in Figure 29. 

Treatment of the Os(ii) precursor [OsGlGp(PPr 3)2] with 2-methyl-3-butyn-2-ol and 1-ethynylcyclohexanol in toluene at 85 °G results in the formation of the neutral alkenyl vinylidenes [OsGl =G=G(H)R Gp(PPr 3)] (R = GMe=GH2, 1-cyclohexenyl) via release of PPr 3. Intermediate species containing these propargylic alcohols 7r-coordinated to osmium could be isolated working at RT. The related allenyl vinylidene [0sGl =G=G(G02Me)G-... 

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