Pilar García-Orduña

DNA binding and cytotoxicity of fluorescent curcumin-based Zn(II) complexes

Two new heteroleptic pentacoordinated Zn(II) complexes (1 and 2) containing 4,4′-disubstituted 2,2′-bipyridines as the main ligand and curcumin (curc) as an ancillary ligand have been synthesized, spectroscopically and structurally characterized, and tested in vitro towards different human cancer cell lines. While the nitrogen ligands are almost inactive, Zn(II) curc derivatives 1 and 2 show promising and selective anticancer properties. In particular the curc Zn(II) complex 1 shows the strongest growth inhibition in all cell lines, being even more effective than the pure curc in the LAN-5 neuroblastoma cell line. Furthermore, the curc moiety makes the complexes 1 and 2 fluorescent, a feature enabling investigation of their interaction with DNA through a new optical method previously tested with the reference fluorescent intercalator ethidium bromide. This analysis demonstrates that the interaction mode of curc, 1 and 2 with DNA in the double helix favors their alignment perpendicular to the DNA axis, suggesting a partial inter-base intercalation of these Zn(II) complexes.

Direct Access to Parent Amido Complexes of Rhodium and Iridium through NH Activation of Ammonia

Financial support from CONSOLIDER INGENIO-2010 program under the projects MULTICAT (CSD2009-00050) and Factoria de Cristalizacion (CSD2006-0015). P.G.O. acknowledges financial support from the CSIC “JAE-Doc” program.

Terminal and bridging parent amido 1,5-cyclooctadiene complexes of rhodium and iridium.

The ready availability of rare parent amido d(8) complexes of the type [{M(μ-NH2)(cod)}2] (M=Rh (1), Ir (2); cod=1,5-cyclooctadiene) through the direct use of gaseous ammonia has allowed the study of their reactivity. Both complexes 1 and 2 exchanged the di-olefines by carbon monoxide to give the dinuclear tetracarbonyl derivatives [{M(μ-NH2)(CO)2}2 ] (M=Rh or Ir). The diiridium(I) complex 2 reacted with chloroalkanes such as CH2Cl2 or CHCl3, giving the diiridium(II) products [(Cl)(cod)Ir(μ-NH2)2Ir(cod)(R)] (R=CH2Cl or CHCl2) as a result of a two-center oxidative addition and concomitant metal-metal bond formation. However, reaction with ClCH2CH2Cl afforded the symmetrical adduct [{Ir(μ-NH2)(Cl)(cod)}2] upon release of ethylene. We found that the rhodium complex 1 exchanged the di-olefines stepwise upon addition of selected phosphanes (PPh3, PMePh2, PMe2Ph) without splitting of the amido bridges, allowing the detection of mixed COD/phosphane dinuclear complexes [(cod)Rh(μ-NH2)2Rh(PR3)2], and finally the isolation of the respective tetraphosphanes [{Rh(μ-NH2)(PR3)2}2]. On the other hand, the iridium complex 2 reacted with PMe2 Ph by splitting the amido bridges and leading to the very rare terminal amido complex [Ir(cod)(NH2)(PMePh2)2]. This compound was found to be very reactive towards traces of water, giving the more stable terminal hydroxo complex [Ir(cod)(OH)(PMePh2)2]. The heterocyclic carbene IPr (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) also split the amido bridges in complexes 1 and 2, allowing in the case of iridium to characterize in situ the terminal amido complex [Ir(cod)(IPr)(NH2)]. However, when rhodium was involved, the known hydroxo complex [Rh(cod)(IPr)(OH)] was isolated as final product. On the other hand, we tested complexes 1 and 2 as catalysts in the transfer hydrogenation of acetophenone with iPrOH without the use of any base or in the presence of Cs2CO3, finding that the iridium complex 2 is more active than the rhodium analogue 1.

The dehydrogenation of alcohols through a concerted bimetallic mechanism involving an amido-bridged diiridium complex

Financial support from the CONSOLIDER INGENIO-2010 program under the projects MULTICAT (CSD2009-00050) and Factoria de Cristalizacion (CSD2006-0015), and the DGA-ESF are acknowledged. P.G.O. acknowledges financial support from the CSIC “JAE-Doc” program, a contract co-funded by the ESF.

Temperature Dual Enantioselective Control in a Rhodium‐Catalyzed Michael‐Type Friedel–Crafts Reaction: A Mechanistic Explanation

By changing the temperature from 283 to 233 K, the S (99 % ee) or R (96 % ee) enantiomer of the Friedel-Crafts (FC) adduct of the reaction between N-methyl-2-methylindole and trans-β-nitrostyrene can be obtained by using (SRh ,RC )-[(η(5) -C5 Me5 )Rh{(R)-Prophos}(H2 O)][SbF6 ]2 as the catalyst precursor. This catalytic system presents two other uncommon features: 1) The ee changes with reaction time showing trends that depend on the reaction temperature and 2) an increase in the catalyst loading results in a decrease in the ee of the S enantiomer. Detection and characterization of the intermediate metal-nitroalkene and metal-aci-nitro complexes, the free aci-nitro compound, and the FC adduct-complex, together with solution NMR measurements, theoretical calculations, and kinetic studies have allowed us to propose two plausible alternative catalytic cycles. On the basis of these cycles, all the above-mentioned observations can be rationalized. In particular, the reversibility of one of the cycles together with the kinetic resolution of the intermediate aci-nitro complexes account for the high ee values achieved in both antipodes. On the other hand, the results of kinetic measurements explain the unusual effect of the increment in catalyst loading.

Tuning the activity and selectivity of iridium-NSiN catalyzed CO2 hydrosilylation processes

The catalytic activity of various Ir-NSiN-type complexes, containing different ancillary ligands and/or modified NSiN-type ligands, as catalyst precursors for CO2 hydrosilylation has been studied. The results from these experiments evidenced that the activity and selectivity of the above mentioned catalytic systems depend on the nature of the ancillary ligands as well as on the reaction parameters (temperature and CO2 pressure). Thus, the best catalytic performance has been achieved at 328 K and 8 bar of CO2 using the complex [Ir(H)(CF3CO2)(NSiN*)(coe)] (NSiN* = fac-bis-(4-methylpyridine-2-yloxy)methylsilyl) as a catalyst precursor.

C-NH2 bond formation mediated by iridium complexes.

In the presence of phosphanes (PR3 ), the amido-bridged trinuclear complex [{Ir(μ-NH2 )(tfbb)}3 ] (tfbb=tetrafluorobenzobarrelene) transforms into mononuclear discrete compounds [Ir(1,2-η(2) -4-κ-C12 H8 F4 N)(PR3 )3 ], which are the products of the CN coupling between the amido moiety and a vinylic carbon of the diolefin. An alternative synthetic approach to these species involves the reaction of the 18 e(-) complex [Ir(Cl)(tfbb)(PMePh2 )2 ] with gaseous ammonia and additional phosphane. DFT studies show that both transformations occur through nucleophilic attack. In the first case the amido moiety attacks a diolefin coordinated to a neighboring molecule following a bimolecular mechanism induced by the highly basic NH2 moiety; the second pathway involves a direct nucleophilic attack of ammonia to a coordinated tfbb molecule.

Catalytic Hydrodechlorination of Benzyl Chloride Promoted by Rh–N‐heterocyclic Carbene Catalysts

The rhodium(I) complexes [Rh(Cl)(COD)(R-NHC-(CH2 )3 Si(OiPr)3 )] [COD=cyclooctadiene; R=2,6-diisopropylphenyl (1 a); n-butyl (1 b)] are effective catalyst precursors for the homogeneous hydrodechlorination of benzyl chloride using HSiEt3 as hydrogen source. This reaction is selective to the formation of toluene. However, in presence of a stoichiometric amount of potassium tert-butoxide (KtBuO) the formation of mixtures containing toluene together with 17-19 mol % of the C--C homocoupling product, namely PhCH2 CH2 Ph, is observed. A mechanism proposal based on experimental insights and theoretical calculations at the DFT level that allows explanation of the experimental findings is included. Moreover, the heterogeneous catalytic system based on catalyst 1 a supported on MCM-41 has been demonstrated to be effective for the solvent-free hydrodechlorination of benzyl chloride using HSiEt3 and HSiMe(OSiMe3 )2 .

Grafting of Copper(I)–NHC Species on MCM‐41: Homogeneous versus Heterogeneous Catalysis

The copper(I) complexes [Cu(X){2,6‐diisopropylphenyl–NHC–(CH2)3Si(OiPr)3}] (X=Cl (2 a); I (2 b), NHC=N‐heterocyclic carbene) have been synthesized and characterized. Furthermore, the structure of 2 b has been confirmed by X‐ray diffraction studies. Complex 2 a has been successfully anchored in MCM‐41 to afford 2–MCM‐41. The activity of both the homogeneous, 2 a, and heterogeneous, 2–MCM‐41, catalysts in acetophenone hydrosilylation with HSiEt3 and [3+2] cycloaddition of benzyl azide and phenylacetylene has been investigated. The heterogeneous catalyst exhibits catalytic activity for the cycloaddition reaction though, unexpectedly, shows no catalytic activity for hydrosilylation.

Rhodium-Catalyzed Dehydrogenative Silylation of Acetophenone Derivatives: Formation of Silyl Enol Ethers versus Silyl Ethers

A series of rhodium-NSiN complexes (NSiN=bis (pyridine-2-yloxy)methylsilyl fac-coordinated) is reported, including the solid-state structures of [Rh(H)(Cl)(NSiN)(PCy3 )] (Cy=cyclohexane) and [Rh(H)(CF3 SO3 )(NSiN)(coe)] (coe=cis-cyclooctene). The [Rh(H)(CF3 SO3 )(NSiN)(coe)]-catalyzed reaction of acetophenone with silanes performed in an open system was studied. Interestingly, in most of the cases the formation of the corresponding silyl enol ether as major reaction product was observed. However, when the catalytic reactions were performed in closed systems, formation of the corresponding silyl ether was favored. Moreover, theoretical calculations on the reaction of [Rh(H)(CF3 SO3 )(NSiN)(coe)] with HSiMe3 and acetophenone showed that formation of the silyl enol ether is kinetically favored, while the silyl ether is the thermodynamic product. The dehydrogenative silylation entails heterolytic cleavage of the Si-H bond by a metal-ligand cooperative mechanism as the rate-determining step. Silyl transfer from a coordinated trimethylsilyltriflate molecule to the acetophenone followed by proton transfer from the activated acetophenone to the hydride ligand results in the formation of H2 and the corresponding silyl enol ether.