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Activation of Propargylic Alcohols Derived from Hormonal Steroids by the Indenyl−Ruthenium(II) Complex [RuCl(η5-C9H7)(PPh3)2]: Experimental and Theoretical Evidence of an Allenylidene−Vinylvinylidene Equilibrium

AuthorsCadierno, Victorio; Conejero, Salvador ; Gamasa, María Pilar; Gimeno, José; Rodríguez, Miguel A.
Hormonal Steroids
Allenylidene-Vinylvinylidene equilibrium
Kinetic control
Issue Date11-Dec-2001
PublisherAmerican Chemical Society
CitationOrganometallics 21(1): 203-209 (2002)
AbstractThe indenyl−ruthenium(II) complex [RuCl(η5-C9H7)(PPh3)2] (1) reacts with ethisterone (2a), 17α-ethynylestradiol (2b), and mestranol (2c), in methanol and in the presence of NaPF6, to afford equilibrium mixtures containing the corresponding allenylidene 3a−c and vinylvinylidene 4a−c tautomers. Deprotonation of these mixtures with K2CO3 allows the preparation of σ-enynyl derivatives 5a−c, which can be selectively alkylated with MeOSO2CF3 to yield disubstituted vinylvinylidene complexes 6a−c. Displacement of these equilibriums can also be accomplished by treatment of the reaction mixtures with acetonitrile or PMe2Ph. Thus, while in the first case terminal 1,3-enynes 7a−c are selectively obtained by demetalation of vinylvinylidenes 4a−c, phosphonio-alkynyl complexes 9a−c are exclusively formed in the second case as the result of the nucleophilic addition of PMe2Ph on the electrophilic Cγ atom of allenylidenes 3a−c. Ab initio molecular orbital calculations on the models [Ru{ C C C(H)CH3}(η5-C5H5)(PH3)2]+ and [Ru{ C C(H)CH CH2}(η5-C5H5)(PH3)2]+ show that the vinylvinylidene tautomer is only 2.1 kcal/mol more stable than the allenylidene. The spontaneous tautomerization process between both complexes, which involves a [1,3]-hydrogen sigmatropic rearrangement, requires an activation energy of 66.5 kcal/mol.
Description7 páginas, 1 figura, 1 tabla, esquemas.
Publisher version (URL)http://dx.doi.org/10.1021/om010672d
Appears in Collections:(IIQ) Artículos
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