192653-44-4Relevant academic research and scientific papers
Ligand effects in the hydrogenation of methacycline to doxycycline and epi-doxycycline catalysed by rhodium complexes molecular structure of the key catalyst [closo-3,3-(η2,3-c7h7ch2)-3,1,2-rhc2b9h11]
Felekidis,Goblet-Stachow,Liegeois,Pirotte,Delarge,Demonceau,Fontaine,Noels,Chizhevsky,Zinevich,Bregadze,Dolgushin,Yanovsky,Struchkov
, p. 405 - 412 (1997)
The catalytic reduction of the exocyclic methylene group of methacycline (A) leads to the formation of two diastereoisomers, doxycycline (B, the α-epimer) and 6-epi-doxycycline (C, the β-epimer), with a selectivity which markedly depends on the nature of hydrocarbon and carborane ligands of closo-(π-cyclodienyl)rhodacarborane catalysts. Neutral norbornadienyl complexes with unsubstituted carborane ligands [closo-3,3-(η2,3-C7H7CH2)-3,1,2-RhC2B9H11] (1) and [closo-2,2-(η2,3-C7H7CH2)-2,1,7-RhC2B9H11] (7) are more active and afford higher selectivity in the formation of doxycycline than those having mono-or di-substituents at the carborane cage, [closo-3,3-(cyclodienyl)-1-R-2-R′-3,1,2-RhC2B9H9] (R = H, R′ = Me, PhCH2; R = R′ = Me; cyclodienyl = η2,3-C7H7CH2 or η-C10H13) as well as those from the closely related series of η5-cyclopentadienyl complexes [(η2,3-C7H7CH2)Rh(η5-C5Rn)]+PF-6 (Rn = H5, Me5, or H2-1,2,4-Ph3). Mechanistic aspects of the hydrogenation reaction of methacycline are sketched. The results of the X-ray diffraction study of the best catalyst 1 are reported.
