Ring‐functionalized niobocene complexes

Abstract

4 ) was synthesized and characterized by electron paramagnetic resonance. Three structures were determined by X-ray diffraction analysis and revealed the expected bent metallocene structure with two cyclopentadienyl ligands and two chlorides coordinated to niobium in the oxidation state IV. Chlorides and the centroids of the η 5 -bonded cyclopentadienyl rings define a distorted tetrahedron. The cytotoxicity study has demonstrated that substitution with methoxybenzyl groups can lead to highly active species, but the activity strongly varies with the number and positions of the methoxy groups in the benzene ring. The most active species under study -{2,4-(MeO) 2 C 6 H 3 CH 2 C 5 H 4 } 2 NbCl 2 -has a maximal inhibitory concentration value comparable with cisplatin.

Recent Advances in the Chemistry of Pentafulvenes

“…235 More recently, the powerful superhydride reagent LiBEt 3 H has been widely applied to a large variety of 6-arylfulvenes. This method readily gives access to the corresponding lithium cyclopentadienyl precursors for direct use in the synthesis of titanocene, 236−246 zirconocene, 247 vanadocene, 248−250 niobocene, 251 molybdocene, 252 and tin 253 complexes (Scheme 87).…”

Cyclopentadienyl Molybdenum(II) Compounds Bearing Ether and Thioether Functions in the Side Chain: Synthesis, Characterization, and Cytotoxic/Cytostatic Studies

“…Strong effect of coordinated chelating ligand on in vitro cytotoxic activity of [(η 5 ‐Cp’)Mo(CO) 2 (L)][BF 4 ] has been well documented already in the early stage of investigation on mouse Ehrlich ascites tumor cells [18] and human MOLT‐4 leukemia cells [19] while effects of cyclopentadienyl (Cp) ligand substitution seemed to be negligible for a long time [19,20] as several substitution patterns brought only minor lowering of half‐maximal inhibitory concentrations (IC 50 ). Studies on MOLT‐4 cell line documented a high cytotoxicity for various species bearing modified Cp/Ind ring and following N,N’ ‐chelating ligands: 1,10‐phenanthroline (phen), 4,7‐diphenyl‐1,10‐phenanthroline (4,7‐Ph 2 Phen), 5‐amino‐1,10‐phenanthroline (5‐NH 2 Phen) [19–22] . Indenyl molybdenum compounds bearing 4,7‐Ph 2 Phen and 2,2’‐biquinoline (bq) exhibit high in vitro activity against human colorectal cancer cells HT‐29 and gastric cancer cells MKN45, GP‐202 and GP‐220 [18] .…”

“…(5-NH 2 Phen). [19][20][21][22] Indenyl molybdenum compounds bearing 4,7-Ph 2 Phen and 2,2'-biquinoline (bq) exhibit high in vitro activity against human colorectal cancer cells HT-29 and gastric cancer cells MKN45, GP-202 and GP-220. [18] However, scrutinizing a wider range of compounds bearing modified Cp/Ind ring has shown unusually high cytotoxicity against MOLT-4 and HL-60 leukemia cells for particular complexes of 2,2'-bipyridine (bpy) [23] even though parent cyclopentadienyl species [(η 5 -Cp)Mo(CO) 2 (bpy)][BF 4 ] is almost inactive.…”

Regioselective Synthesis of 6-Chlorofulvene and 6-Aminofulvene via Keto–Enol Tautomerism

“…Because of the unique conjugated systems, fulvene derivatives are very important for the synthesis of natural products and metallocene complexes. − In our previous works, we found that 6′-hydroxyfluvene 1 was almost the exclusive form in the equilibrium with 1-1, because it could be stabilized by intramolecular hydrogen-bonding (Scheme ). Compound 1 can readily react with n -butylamine to give amination product 3 - 1 . , On the basis of the result, we continued to study regioselectivity in the chlorination reaction of 6′-hydroxyfluvene 1 by treating it with POCl 3 and DMF.…”