Cristina Tubaro

Blue-emitting dinuclear N-heterocyclic dicarbene gold(I) complex featuring a nearly unit quantum yield.

Dinuclear N-heterocyclic dicarbene gold(I) complexes of general formula [Au(2)(RIm-Y-ImR)(2)](PF(6))(2) (R = Me, Cy; Y = (CH(2))(1-4), o-xylylene, m-xylylene) have been synthesized and screened for their luminescence properties. All the complexes are weakly emissive in solution whereas in the solid state some of them show significant luminescence intensities. In particular, crystals or powders of the complex with R = Me, Y = (CH(2))(3) exhibit an intense blue emission (λ(max) = 450 nm) with a high quantum yield (Φ(em) = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au···Au distance (3.272 Ǻ). Time dependent density functional theory (TDDFT) calculations have been used to calculate the UV/vis properties of the ground state as well as of the first excited state of the complex, the latter featuring a significantly shorter Au···Au distance.

Synthesis and biological assays on cancer cells of dinuclear gold complexes with novel functionalised di(N-heterocyclic carbene) ligands.

New dinuclear di(N-heterocyclic carbene) silver(I), gold(I) and gold(III) complexes have been synthesised and their antiproliferative effects towards various cancer cell lines have been screened. The di(N-heterocyclic carbene) ligands have a propylene linker between the carbene moieties and the imidazole backbone has been functionalised with a 1-benzyl- or 1-PEG-1,2,3-triazole ring (PEG=poly(ethylene glycol)) via a CuAAC (copper azido alkyne cycloaddition) reaction. The resulting gold(I) and gold(III) complexes display an antiproliferative activity superior to that of the unfunctionalised pristine complexes together with a higher selectivity towards cancerous cells with respect to healthy cells.

Reactions of Diazo Compounds with Alkenes Catalysed by [RuCl(cod)(Cp)]: Effect of the Substituents in the Formation of Cyclopropanation or Metathesis Products

The reaction of diazo compounds with alkenes catalysed by complex [RuCl(cod)(Cp)] (cod = 1,5-cyclooctadiene, Cp = cyclopentadienyl) has been studied. The catalytic cycle involves in the first step the decomposition of the diazo derivative to afford the reactive [RuCl(Cp){=C(R(1))R(2)}] intermediate and a mechanism is proposed for this step based on a kinetic study of the simple coupling reaction of ethyl diazoacetate. The evolution of the Ru-carbene intermediate in the presence of alkenes depends on the nature of the substituents at both the diazo N(2)=C(R(1))R(2) (R(1), R(2) = Ph, H; Ph, CO(2)Me; Ph, Ph; C(R(1))R(2) = fluorene) and the olefin substrates R(3)(H)C=C(H)R(4) (R(3), R(4) = CO(2)Et, CO(2)Et; Ph, Ph; Ph, Me; Ph, H; Me, Br; Me, CN; Ph, CN; H, CN; CN, CN). A remarkable reactivity of the complex was recorded, especially towards unstable aryldiazo compounds and electron-poor olefins. The results obtained indicate that either cyclopropanation or metathesis products can be formed: the first products are favoured by the presence of a cyano substituent at the double bond and the second ones by a phenyl.

Alkyne hydroarylation with palladium(II) complexes bearing chelating N-heterocyclic ligands: effect of non-coordinated nitrogens on catalyst efficiency

Palladium(II) complexes with chelating N-heterocyclic ligands bearing uncoordinated nitrogen atoms are efficient catalysts in the hydroarylation of alkynes, giving selectively trans-hydroarylation of the triple bond. The catalytic efficiency of these systems is markedly dependent on the strength of the acid added as reaction promoter, thus suggesting the formation, via ligand protonation, of highly electrophilic metal intermediates, which are responsible for the observed selectivity.

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

Summary Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh3). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction.

Reaction of platinum acetate with phosphines and molecular structure of trans-[Pt(OAc)2(PPh3)2]

An improved synthesis of platinum acetate is reported in detail. This tetrameric complex reacts with PPh3 or P � /n-Bu3 at room temperature to give the thermodynamically unstable bis-substituted trans -[Pt(OAc)2L2] complexes, which are not easily accessible via other routes. The structure of the new compound trans -[Pt(OAc)2(PPh3)2] has been determined by X-ray analysis. # 2003 Elsevier B.V. All rights reserved.

Alkyne Hydroarylation in Ionic Liquids Catalyzed by Palladium(II) Complexes

The efficiency of dicarbene palladium(II) complexes and of simple palladium(II) acetate as catalysts for alkyne hydroarylation under liquid-liquid biphasic conditions involving an ionic liquid as the catalyst-containing phase is investigated. The results obtained under these conditions, both in terms of activity and selectivity, are compared with those previously obtained under homogeneous conditions. The catalytic efficiency of the systems is found to be markedly dependent on the nature of the anion of the ionic liquid. Suitable anions are found to significantly improve the catalytic performance in comparison to homogeneous conditions. Preliminary investigations on the recyclability of the system as well as the on advantages of using an acidic ionic liquid are also carried out.

Dinuclear complexes of silver(I) and gold(I) with macrocyclic dicarbene ligands bearing a 2,6-lutidinyl bridge: synthesis, structural analysis and dynamic behaviour in solution

Dinuclear silver(I) and gold(I) complexes with nonsymmetric macrocyclic dicarbene ligands featured by a 2,6-lutidinyl bridge as well as by a linker 3–4 carbon atoms long (1,3-propylene, o-xylylene, and 1,4-butylene) between two N-heterocyclic carbene groups have been prepared and structurally characterised. All complexes are formed as a mixture of two isomers, which have been interpreted as syn and anti isomers. Whereas in the case of the gold(I) complexes the two isomeric forms do not interconvert at a measurable rate, fast interconversion is recorded with the silver(I) complexes. Finally, the capability of the gold(I) complexes to act as organometallic ligands towards additional group 11 metal centres has been preliminarily evaluated.

Metal complexes with di(N-heterocyclic carbene) ligands bearing a rigid ortho-, meta or para-phenylene bridge

Three novel dinuclear bis-dicarbene silver(i) complexes of general formula [Ag2(MeIm-phenylene-MeIm)2](PF6)2 (Im = imidazol-2-ylidene) were synthesized. The corresponding copper(i) and gold(i) complexes were obtained by transmetalation of the di(N-heterocyclic carbene) ligand from the silver(i) species, and both coordination geometry and stoichiometry are maintained for all three group 11 metals as expected. The photophysical properties of the Ag(i) and Au(i) complexes were also investigated and discussed; in particular the most strongly emitting complex was also studied via DFT calculations. In addition, the ruthenium(ii) and iridium(iii) complexes [RuCl(MeIm-(o-phenylene)-MeIm)(p-cym)](PF6) and [IrClCp*(MeIm-(o-phenylene)-MeIm)](PF6) were prepared and shown to present in these cases a chelating coordination of the di(N-heterocyclic carbene) ligand.

Insights into the Halogen Oxidative Addition Reaction to Dinuclear Gold(I) Di(NHC) Complexes

Gold(I) dicarbene complexes [Au2 (MeIm-Y-ImMe)2 ](PF6 )2 (Y=CH2 (1), (CH2 )2 (2), (CH2 )4 (4), MeIm=1-methylimidazol-2-ylidene) react with iodine to give the mixed-valence complex [Au(MeIm-CH2 -ImMe)2 AuI2 ](PF6 )2 (1 a(I) ) and the gold(III) complexes [Au2 I4 (MeIm-Y-ImMe)2 ](PF6 )2 (2 c(I) and 4 c(I) ). Reaction of complexes 1 and 2 with an excess of ICl allows the isolation of the tetrachloro gold(III) complexes [Au2 Cl4 (MeIm-CH2 -ImMe)2 ](PF6 )2 (1 c(Cl) ) and [Au2 Cl4 (MeIm-(CH2 )2 -ImMe)2 ](Cl)2 (2 c(Cl) -Cl) (as main product); remarkably in the case of complex 2, the X-ray molecular structure of the crystals also shows the presence of I-Au-Cl mixed-sphere coordination. The same type of coordination has been observed in the main product of the reaction of complexes 3 or 4 with ICl. The study of the reactivity towards the oxidative addition of halogens to a large series of dinuclear bis(dicarbene) gold(I) complexes has been extended and reviewed. The complexes react with Cl2 , Br2 and I2 to give the successive formation of the mixed-valence gold(I)/gold(III) n a(X) and gold(III) n c(X) (excluding compound 1 c(I) ) complexes. However, complex 3 affords with Cl2 and Br2 the gold(II) complex 3 b(X) [Au2 X2 (MeIm-(CH2 )3 -ImMe)2 ](PF6 )2 (X=Cl, Br), which is the predominant species over compound 3 c(X) even in the presence of free halogen. The observed different relative stabilities of the oxidised complexes of compounds 1 and 3 have also been confirmed by DFT calculations.