Ruthenium(0) complexes with triazolylidene spectator ligands: Oxidative activation for (de)hydrogenation catalysis

Transmetallation of silver triazolylidene intermediates with the ruthenium(0) precursor [Ru(Cp]O) (CO)2]2 afforded low-valent ruthenium(0) complexes containing a triazole-derived NHC ligand (Cp] O \ubc 3,4-di(4-methoxyphenyl)-2,5-diphenyl-cyclopentadienone). Protonation of the carbonyl group of the Cp]O ligand significantly reduces the p character of the RueCO bond as deduced from nCO analysis. The new triazolylidene ruthenium(0) complexes were evaluated as catalyst precursors in transfer hydrogenation of 4-fluoro-acetophenone and in the acceptorless dehydrogenation of benzyl alcohol. Low activities were noted, though in both reactions, catalytic performance is markedly increased when cerium( IV) was added. Electrochemical analysis indicates that activation of the catalyst precursor proceeds via cerium-mediated oxidation of the ruthenium center, which facilitates dissociation of a CO ligand to enter the catalytic cycle. Such oxidative activation of catalyst precursors may be of more general scope

Glycol methyl ether and glycol amine substituted titanocenes as antitumor agents

6-[4-(2-Methoxyethoxy)phenyl]fulvene (3a) and 6-(4-[2-(di-methylamino)ethoxy]phenyl)fulvene (3b) were prepared as starting materials for the synthesis of three dofferent classes of titanocenes, which are ansa-titanocenes, diarylmethyl-substituted titanicenes and benzyl-substituted titanocenes and benyzyl-subtituted titanocenes. Because the synthetic possibilities seem to be limited, only ansa-titanocene {1,2-bis(cyclopentadienyl)-1,2-bis[4-(2-methoxyethoxy)phenyl]ethanediyl}titanium dichloride (4a) and benzyl-substituted titanocene bis-{[4-(2-methoxyethoxy)benzyl]cyclopentadienyl}titantium(IV) dichloride (6a) were obtained and characterised. The change in the substitution pattern f the phenyl moiety from an oxygen atom to a nitrogen atom had such a big influence on the reaction that not one compound of the threee titanocene classes could be synthesised, and it was also not possible to obtain diarylmethyl-substituted titanocenes with the use of either of the fulvenes. When benzyl-substituted titanocene 6a was tested agianst pig kidney cells (LLC-PK), an antiproliferative effect that result in an IC50 value of 43 mu m, was observed. This IC50 value is in the lower range of the cytotoxicities evaluated for titanocenes up to now. ansa-Titanocene 4a surprisingly showed, when tested on the same cell line, a proliferative effect together with a fast rate of hydrolysis

Heteroaryl substituted titanocenes as potential anti-cancer drugs

From the reaction of Super Hydride (LiBEt3H) with 6-(furyl)fulvene (1a), 6-(thiophenyl)fulvene (1b) or 6-(N-methyl-pyrrole)fulvene (1c) the corresponding lithium cyclopentadienide intermediates (2a-c) were obtained. These intermediates were reacted with titanium tetrachloride and bis-[(furyl-2-cyclopentadienylmethane)] titanium(IV) dichloride (3a) and bis-[(thiophenyl-2-cyclopentadienylmethane)] titanium(IV) dichloride (3b) and bis-[(N-methylpyrrole-2-cyclopentadienylmethane)] titanium(IV) dichloride (3c) were obtained and subsequently characterised by X-ray crystallography. When titanocenes 3a-c were tested against pig kidney (LLC-PK) cells inhibitory concentrations (IC50) of 1.6 x 10(-4) M, 1.5 x 10(-4) M and 9.1 x 10(-5) M, respectively, were observed. These values represent improved cytotoxicity against LLC-PK, when compared to their corresponding ansa substituted analogues and also in comparison to unsubstituted titanocene dichloride. (c) 2006 Elsevier Inc. All rights reserved

Novel platinum pyridinehydroxamic acid complexes: synthesis, characterisation, X-ray crystallographic study and nitric oxide relaled properties

7nonenoneD. GRIFFITH; BERGAMO A; S. PIN; M. VADORI; H. MÜLLER-BUNZ; G. SAVA; CJ. MARMIOND., Griffith; Bergamo, A; S., Pin; M., Vadori; H., MÜLLER-BUNZ; G., Sava; Cj., Marmio

Electronic vs structural ordering in a manganese(III) spin crossover complex

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