- Acceptor pincer chemistry of osmium: Catalytic alkane dehydrogenation by (CF3PCP)Os(cod)(H)
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Syntheses of osmium analogues of acceptor pincer (CF3PCP)Ru(II) systems are reported. Treatment of [Et4N]2OsCl6 with CF3PCPH at 130 C in ethanol in the presence of Et3N gave the coordinatively saturated anionic carbonyl complex HNEt3 +[(CF3PCP)Os(CO)Cl2]-, which subsequently may be converted to cis-(CF3PCP)Os(CO)2Cl or cis-(CF3PCP)Os(CO)2H by reaction with Me3SiOTf or (Et3Si)2(μ-H)+B(C6F 5)4-, respectively. (CF3PCP)Os(cod)H was obtained in modest yields by thermolysis of Os(cod)(η3-2- methylallyl)2 with CF3PCPH in neat cod under 3 atm of H2 at 130 C. The alkane dehydrogenation activity of (CF 3PCP)Os(cod)H was examined: under identical conditions to previously studied (CF3PCP)Ru(cod)H (1:1 cyclooctane/tert-butylethylene, 200 C), the initial turnover rate for cyclooctene production was 1520 h-1, 75% the rate observed for the ruthenium analogue, but with significantly enhanced catalyst lifetime. Acceptorless cyclodecane dehydrogenation under reflux conditions gave 125 turnovers of cyclodecenes in one hour. Spectroscopic evidence on the nature of the catalyst resting state and catalyst thermal and air stability is presented.
- Gruver, Brian C.,Adams, Jeramie J.,Arulsamy, Navamoney,Roddick, Dean M.
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p. 6468 - 6475
(2013/12/04)
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- Acceptorless dehydrogenation of C-C single bonds adjacent to functional groups by metal-ligand cooperation
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Unprecedented direct acceptorless dehydrogenation of C-C single bonds adjacent to functional groups to form α,β-unsaturated compounds has been accomplished by using a new class of group 9 metal complexes. Metal-ligand cooperation operated by the hydroxycyclopentadienyl ligand was proposed to play a major role in the catalytic transformation.
- Kusumoto, Shuhei,Akiyama, Midori,Nozaki, Kyoko
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supporting information
p. 18726 - 18729
(2014/01/06)
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- Diradical-promoted two-carbon ring-expansion reactions by thermal isomerization: Synthesis of functionalized macrocyclic ketones
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A new method for the smooth and highly efficient preparation of functionalized macrocyclic ketones has been developed. Pyrolysis of medium- and large-ring 3-vinylcycloalkanones by dynamic gas-phase thermo-isomerization (DGPTI) at 600-630° yielded, under insertion of a previously attached vinyl side chain by means of a 1,3-C shift, the corresponding γ,δ- unsaturated cycloalkanones. The yield of the two-carbon ring-expanded ketones greatly depended on the relative ring strains of substrate and product (5-87%, cf. Table 5). The formation of minor amounts of one-carbon ring-expanded cycloalkenes (10%) can be ascribed to a subsequent decarbonylation step. A reaction mechanism involving initial cleavage of the weakest single bond in the molecule has been established (cf. Scheme 6). Recombination within the generated diradical intermediate in terminal vinylogous position led to the observed products, while reclosure gave recovered starting material. Substituents on the vinyl moiety were transferred locospecifically into the ring-expanded products. An isopropenyl group did not significantly affect the isomerization process, whereas substrates bearing a prop-1-enyl group in β-position enabled competing intramolecular H-abstraction reactions, leading to acyclic dienones (cf. Schemes 9-11). DGPTI of the 13-membered analogue directly yielded 4-muscenone, which, upon hydrogenation, led to the valuable musk odorant (±)-muscone. Increasing the steric hindrance on the vinyl moiety gave rise to diminishing amounts of the desired γ,δ-unsaturated cycloalkanones. This novel two-carbon ring-expansion protocol was also successfully applied to 3-ethynylcycloalkanones, giving rise to the corresponding ring-expanded cyclic allenes (cf. Scheme 13).
- Rueedi, Georg,Hansen, Hans-Juergen
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p. 1628 - 1665
(2007/10/03)
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- Photochemistry of Alkenes. 9. Medium-sized cycloalkenes
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The behavior of three medium-sized cycloalkenes cyclooctene (10), cyclodecene (17) and cyclododecene (21) on direct irradiation in pentane and methanol solution has been studied.The results are summarized in Tables 1-3.Irradiation of medium-sized cycloalkenes is a convenient procedure for the preparation of bicyclic products (cf. 13, 14, 19, 20 and 23) through transannular insertion reactions of carbene intermediates (cf. 11, 18, and 22) thought to arise from rearrangement of the 1 state via a 1,2-hydrogen shift.The formation of trans-decalin (20) is in contrast to the reported formation of the cis isomer on base-initiated decomposition of the corresponding tosylhydrazone.None of the three cycloalkenes 10, 17, or 21 underwent competing nucleophilic trapping of the 1 state in methanol, in contrast with other alkenes previously studied.However, cyclododecene (21) afforded the methyl ether 25, which apparently resulted from protonation of the 1(?,?*) state, and the epoxide 26, which is thought to arise from electron transfer to oxygen by the 1 state followed by protonation of the resulting superoxide ion and oxidation of unreacted cyclododecene (21).
- Kropp, Paul J.,Mason, J. Derek,Smith, Gardiner F. H.
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p. 1845 - 1849
(2007/10/02)
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