- Demystifying Cp2Ti(H)Cl and Its Enigmatic Role in the Reactions of Epoxides with Cp2TiCl
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The role of Cp2Ti(H)Cl in the reactions of Cp2TiCl with trisubstituted epoxides has been investigated in a combined experimental and computational study. Although Cp2Ti(H)Cl has generally been regarded as a robust species, its decomposition to Cp2TiCl and molecular hydrogen was found to be exothermic (ΔG = -11 kcal/mol when the effects of THF solvation are considered). In laboratory studies, Cp2Ti(H)Cl was generated using the reaction of 1,2-epoxy-1-methylcyclohexane with Cp2TiCl as a model. Rapid evolution of hydrogen gas was demonstrated, indicating that Cp2Ti(H)Cl is indeed a thermally unstable molecule, which undergoes intermolecular reductive elimination of hydrogen under the reaction conditions. The stoichiometry of the reaction (Cp2TiCl:epoxide = 1:1) and the quantity of hydrogen produced (1 mol per 2 mol of epoxide) is consistent with this assertion. The diminished yield of allylic alcohol from these reactions under the conditions of protic versus aprotic catalysis can be understood in terms of the predominant titanium(III) present in solution. Under the conditions of protic catalysis, Cp2TiCl complexes with collidine hydrochloride and the titanium(III) center is less available for "cross-disproportionation" with carbon-centered radicals; this leads to byproducts from radical capture by hydrogen atom transfer, resulting in a saturated alcohol.
- Gordon, Jonathan,Hildebrandt, Sven,Dewese, Kendra R.,Klare, Sven,Gans?uer, Andreas,Rajanbabu,Nugent, William A.
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p. 4801 - 4809
(2019/01/08)
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- Catalytic hydrogen atom transfer (HAT) for sustainable and diastereoselective radical reduction
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Going cyclic! A catalytic cycle and cyclic transition states enable a novel sustainable and catalytic hydrogen atom transfer (HAT) for highly diastereoselective radical reductions. Readily available nontoxic silanes are the terminal reductants for epoxides that are opened by bifunctional titanocene(III) hydride catalysts. Copyright
- Gansaeuer, Andreas,Klatte, Max,Braendle, Gerhard M.,Friedrich, Joachim
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p. 8891 - 8894
(2012/10/08)
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- INTRAMOLECULAR ALKYLATION OF VINYLGERMANES AND IODODEGERMYLATION OF 1-CYCLOALKENYLGERMANES
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Whereas 2-methyl-2,3-epoxy-6-triethylgermyl-6-tridecene gave the expected alkylidenecyclopentanol upon treatment with TiCl4, 5-triethylgermyl-5-dodecenal dimethyl acetal provided the unexpected cyclohexene derivative.Transformation of 1-tri-ethylgermylcyc
- Oda, Hiroji,Oshima, Koichiro,Nozaki, Hitosi
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