Titanocene Dihalides and Ferrocenes Bearing a Pendant alpha-D-Xylofuranos-5-yl or alpha-D-Ribofuranos-5-yl Moiety. Synthesis, Characterization, and Cytotoxic Activity
Abstract
Titanocene dichlorides of general formula [(eta(5)-C5H5)(eta(5)-C5H4R)TiCl2] (where R = 5-deoxy-1,2-di-O-isopropylidene-3-O-benzyl-alpha-D-xylofuranos-5-yl (Xylf) (8a); R = 5-deoxy-1,2-di-O-isopropylidene-3-O-benzyl-alpha-D-ribofuranos-5-yl (Ribf) (8b)) and [(eta(5)-C5H4R)(2)TiCl2] (R = Xylf (9a); R = Ribf (9b)) were prepared by reaction of the corresponding lithium cyclopentadienides 7a,b with an equimolar amount of [(eta(5)-C5H5)TiCl3] or a 0.5 mol amount of [TiCl4(THF)(2)]. Titanocene difluorides of the general formula [(eta(5)-C5H4R1)(eta(5)-C5H4R2)TiF2] (R-1 = H and R-2 = Ribf (10); R-1 = R-2 = Xylf (11a); R-1 = R-2 = Ribf (11b)) were obtained by fluorination of the corresponding titanocene dichlorides 8b and 9 with the fluorinating agent {2-(CH2NMe2)C6H4-kappa C,N}(n-Bu)(2)SnF in high yields.
Alternatively, complexes 11 were prepared in a straightforward way by direct reaction of [TiF4(THF)(2)] with 2 equiv of the corresponding lithium cyclopentadienide 7a,b. Ferrocene complexes [(eta(5)-C5H4R)(2)Fe] (R = Xylf (12a); R = Ribf (12b)) were synthesized by metathesis of 2 equiv of lithium cyclopentadienide 7a,b and 1 equiv of anhydrous FeCl2.
Deprotection of the benzyl group in ferrocenes 12 proceeded cleanly by a catalytic hydrogenation on Pd/C and afforded the ferrocene diols [(eta(5)-C3H4R)(2)Fe] (R = 5-deoxy-1,2-di-O-isopropylidene-alpha-D-xylofuranos-5-yl (Xylf-OH) (14a); R = 5-deoxy-1,2-di-O-isopropylidene-alpha-D-ribofuranos-5-yl (Ribf-OH) (14b)). A scaled up benzyl deprotection with Et3SiH as a hydrogen source led to the replacement of only one benzyl group, which gave the ferrocene alcohol [(eta(5)-C5H4R1)(eta(5)-C5H4R2)Fe] (R-1 = Xylf and R-2 = Xylf-OH (13)).
The prepared complexes were characterized by elemental analysis, melting point determination, NMR, IR, and ESI-MS, and the molecular structure of 9b was determined by X-ray diffraction analysis.