Search

Ruthenium complexes have proved to exhibit antineoplastic activity1,2 related to the interaction of metal ion with DNA nucleobases. It is indeed of great interest to provide new insights on theses cutting-edge studies such as the identification of different coordinative modes of DNA binding sites. This report deals with the reaction between dihydride Ruthenium complex [(PPh3)3Ru(CO)(H)2], 1, and the Thymine Acetic Acid N[CHC(CH3)C(O)NH]CH2C(O)OH THA, as model for nucleobases. The reaction of 1 with THA affords an unstable monohapto acetate hydride complex, which rapidly evolves into elusive intermediates whose nature was evidenced by NMR spectra and proposed by DFT calculation. Crystallizations enable to freeze the species [(PPh3)2Ru(CO)(1-THA)(2-THA)],4, adopting concomitant monohapto (1-O) in the species 2 and the chelate (2-O,O) coordinative fashion modes as in 3. Investigations by the analogue reactions of 1 with acetic acid confirmed the proposed mechanism. Further, the unexpected isolation of intermolecular dimeric crystalline species, [Ru(CO)(PPh3)2(2-N,O[THA(A)];1-O[THA(B)]]2, 3 whose X-ray structure, beside the monohapto acetate coordination, shows a reciprocal interannular four-membered (2-N,O) chelation. This fashion binding mode, displacing phosphine ligand, enables to stabilize the less stable tautomeric form (+10.1 kcalmol-1,calculated at B3LYP/Def2-TZVP level) of thymine. The spectroscopic features will be presented and discussed in comparison with X-ray molecular structures and DFT calculations.

The use of silylated ligands such as [RC5H4(CH2)2OSiMe3 R=H, SiMe3] constitutes an efficient method to generate p-coordination and/or metal-alkoxy complexes [Firenze]. Upon the favoured release of Me3SiCl, [1] the silyl-mediated synthesis is an efficient strategy to afford nucleophilic additions under milder condition. The silyl-fluorenide [SiMe3Flu-, Flu=C13H8] with propylene oxide causes prompt O-silyl migration to give [Flu(CH2CH(Me)OSiMe3]- to obtain (scheme1): A) p- Rh-coordination. B) Monohapto s-1Flu(CH2CHMeOSiMe3)TiCl3(THF)2 1, which forms h5- Flu(CH2CHMeOSiMe3)TiCl3 2 under thermal treatment. C) Siloxy-silyl Fluorene derivative, which can be viewed as a synthone of the corresponding dianion. With the aim of extending the chemistry of Cp- alkoxide Ti complexes [2] to p--extended ligands, we explored the reaction of TiCpCl3 with Flu derivatives bearing alcohol- or siloxy-moieties [C13H9(CH2CH(Me)OR)] [R=H FluOH a; R=SiMe3 FluOSi b]. Both a and b give rise to new alkoxy-Ti species FluOTiCpCl2 3, via releasing of [HPy]Cl (scheme 2). X-ray structures of a and 3 will be reported. [1] Trouvé G.; Laske D.A.; Meetsma A.; Teuben J.H. J. Organomet. Chem. 1996, 511, 255; Christie S.D.R.; Man K.W.; Whitby R.J.; Slawin, A.M.Z, Organomet. 1999, 18, 348 [2] Turner L.E., Thorn M.G., Swartz R.D., Chesnut R.W., Fanwick P.E., Rothwell I.P., Dalton Trans., 2003, 4580.

The nucleophylic addition of lithium fluorenyl to an excess of racemic propylene oxide forms bifunctionalized fluorenes (80%). The mixture presents substantial diasteromeric selection with enhancement of the racemic (R,R or S,S) with respect to meso form (R,S) (2.6 : 1). This effect can be ascribed to the identification of the preferred chiral conformation in the intermediate step (scheme 1). The resulting species, having memory of chirality (1) of the first-tethered side arm, adds preferentially the second having homochiral conformation. Spectroscopic features and X-ray crystal structure determination of the racemic, meso and enantiopure forms of 1 will be discussed. The reaction with Cr(CO)3(NCMe)3 and molecular grafting to TiCpCl3 will be also reported. (1). Zhao H.; Hsu D.C.; Carlier P.R. Synthesis 2005, 1, 1-16; J. Gawroński J.; Gawrońska K.; Kwit M.; Kacprzak K.; Rychlewska U. Chirality 2004, 16, 405-413.

In the last decade, knowledge of the chemistry of N-arylnitrenium ions has advanced significantly and continue to attract attention arising from synthetic, theoretical and biological interest. Here we report the reactions of five 2-oxo arylnitrenium-BF3 ions generated from deactivated 2-oxoazidobenzenes, including 2-azidobenzenecarbaldehyde, 1-(2-azidophenyl)-1-ethanone, (2-azidophenyl) (phenyl)methanone , 2-azidobenzoic acid and 2-azidobenzenecarbonitrile, with Lewis acid BF3•OEt2 in the presence of benzene, as a possible source of 2-anilino-oxobenzenes and/or acridines. Synthesis of azido azoles: According to the proton-lithium (or halogen-lithium) exchange reaction via butyllithium, the metallation of the methylimidazole, the methylpyrazole and the thiazole rings occurs regioselectively at the C-2 (or at C-5 when the position-2 is unavailable) and the resulting 2-(or 5-) heteroaryllithium was employed for the azido transfer protocol with tosyl azide.

New Catalysis Methodologies aimed to reduce toxicity for human health and environment constitute a recognized target for Sustainable Chemistry (1). Our studies concern new ligands design and development by using non-injurious solvents, moderate conditions and no waste products. Currently our group is working on projects involving the synthesis and characterization of new water soluble polydentate Cyclopentadienyl ligands, tethering 1-3 alcoholic pendants of the type CpO,O,O = [C5H5-nRn] (n=1,2,3 R = CH(CH2)3CHOH), obtained by one-pot reaction between NaCp and oxirane excess [CH(CH2)3CH]O (Scheme1). The reaction discriminates position and chirality sequence of the cycloalkyl substituents stereocentres {for example (S,R,S) for (1,2,4)-C5H2[C*H(CH2)3CHOH]3}. Coordination to transition metals stereospecifically selects less congested enantioface (pR), affording one unique stereoisomer. Coordinative pi greco-abilities give raise to Mn, Fe and Rh complexes. The nature of complexes has determined by different spectroscopic means (ESI-Ms, UV, ORD, CD, IR, bidimensional and n.O.e. NMR techniques). X-ray diffraction studies on examples of the class (LL)Rh{C5H2[CH(CH2)3CHOH]3} (LL = NBD,CO)(1) species confirm the suggested structure. The [NBDRhCpO,O,O] complexes show a peculiar solubility and high stability in ethanol or water. Currently, we are exploring further coordination abilities of alcoholic pendants towards Titanium centre, to obtain bimetallic complexes. Extension of the described synthetic protocol to test general applicability on further polyfunctionalized pi greco-ligands as Indenyl, Fluorenyl and Thienyl is also under investigation. These experiments are of support to investigate on discrete model the cooperativity exerted by metal of different nature (Rh, Ti) or acidic sites (Ti, OH) inside heterogeneous catalytic structures (zeolites, perowskites or mixed oxides) and to test grafting ability or alterations in the stereo-electronic requisites of immobilized Rh sites. We plan to get insight into hydrophilic Rhodium complexes as promising transfer hydrogenation (2) mediator or polymerization of oxygenated olefins in biphasic catalysis. 1 a Cornils, B.; Herrmann, W.A.; Aqueous-Phase Organ ometallic Catalysis Wiley-VCH ed. 2002. 1 b Cornils B; Herrmann.A. Multiphase Homogenous Catalysis Wiley-VCH ed. 2005. 2 Mebi, C.A.; Frost, B.J.; Organometallics 2005, 24, 2339.

Chelate ligands, combining five electron donor rings with alkoxy units, form complexes that exhibit catalytic activity in olefin polymerization 1,2. In this report we describe the syntheses of five electron donor ligands, bearing alcohol or ether units as alkyl lateral chain substituents, namely CpOH [C5H4R], 1-IndOSi [C9H6R’] or FluOMe [C13H8R’’] [R= CH2CH(Me)OH; R’ = CH(CH2)3CHOSiMe3, R’’ = (CH2)3OMe] ; [1,2] via oxirane ring opening reaction and a variety of novel -Rh COD-containing complexes (1-3).

Recently we focused our attention on the chemistry of hydroxy functionalised π-extended ring systems (1). These ligands have been obtained by one-step nucleophilic addition reaction of cyclopentadienyl or the benzo-condensed homologues indenyl and fluorenyl anions on substituted oxirane, as propylene (CH2CHMe)O and its enantiomerically pure form, styrene (CH2CHPh)O and cyclopentene oxides [CH(CH2)3CH]O. In the case of propylene oxide, reactions have been found to be quantitatively and regiospecifically driven to the less congested epoxide carbon atom. We succeeded in isolating unusual hapticity modes (eta1 or eta3) by reacting [Ind*]- or [Flu*]- with Re carbonyl halides1, whereas the eta5-coordination has been accomplished with FeCl2, yielding substituted metallocenes of the type [eta5-C9H6(CH2CHMe)OSiMe3]2Fe as further examples of planar chirality (2). Reaction between Na[C5H4(CH2CHPhOH)] and [Rh(COD)Cl]2, afforded the desired piano stool complex [eta5-C5H4(CH2CHPhOH)]Rh(COD). 1-S. Cerini, PhD Thesis, University of Bologna, 2004. 2- Paley R.S.; Chem.Rew.; 2002; 102; 1493, and references therein.