Diego del Río

Synthesis, antiapoptotic biological activity and structure of an oxo-vanadium(IV) complex with an OOO ligand donor set

Abstract The oxo–vanadium(IV) complex VO(oda)(H2O)2 (1) (oda=oxydiacetate, O(CH2COO−)2) was obtained by reaction of aerobic aqueous solutions of VO(acac)2 with oxydiacetic acid, O(CH2COOH)2. The antiapoptotic biological activity of 1 was studied in insulin-producing cells. Chemically generated nitric oxide (NO) triggers apoptotic events, such as the appearance of oligonucleosomes in cytosol, and this response was prevented by the presence of 1 in the culture medium. The molecular structure of 1 has been determined by X-ray diffraction analysis.

Reactivity of an anionic Pd(II) metallacycle with CH2X2(X = Cl, Br, I): formal insertion of methylene into a Pd–Caryl bond

Whereas the reaction of the anionic palladium metallacycle [K[Pd(CH2CMe2-o-C6H4)(kappa2-Tp)]] with CH2Cl2 leads to the isolation of the stable Pd(IV) chloromethyl complex [Pd(CH2CMe2-o-C6H4)(kappa3-Tp)(CH2Cl)], the analogous reactions with CH2Br2 and CH2I2 give rise to the six membered metallacycles [Pd(CH2CMe2-o-C6H4(CH2))(kappa3-Tp)X](X = Br or I), as a result of the formal insertion of CH2 into the Pd-C(aryl) bond.

IR and Raman Characterization of the Zincocenes (η5-C5Me5)2Zn2 and (η5-C5Me5)(η1-C5Me5)Zn

The measured Raman and IR spectra of solid, polycrystalline bis(pentamethylcyclopentadienyl)dizinc, (eta(5)-C5Me5)2Zn2, 1, and bis(pentamethylcyclopentadienyl)monozinc, (eta(5)-C5Me5)(eta(1)-C5Me5)Zn, 8, are reported in some detail. The IR spectra of the vapors of 1 and 8 each trapped in a solid Ar matrix at 12 K confirm the essentially molecular character of the solids. The experimental results have been interpreted with particular reference (i) to the corresponding spectra of (68)Zn-enriched samples of the compounds, and (ii) to the spectra simulated by density functional theory (DFT) calculations at the B3LYP level. The marked differences of structure of 1 and 8 contrast with the relatively close similarity of their vibrational spectra, disparities being revealed only on detailed scrutiny, including the effects of (68)Zn enrichment, and primarily at wavenumbers below 1000 cm(-1). The Zn-Zn stretching motion of 1 features not as a single, well-defined mode identifiable with intense Raman scattering but in several normal modes which respond in varying degrees to (68)Zn substitution. A stretching force constant of 1.42 mdyne A(-1) has been estimated for the Zn-Zn bond of 1.

Synthesis and Reactivity of Ene-Diamido and Ene-Diolato ((Trimethylsilyl)- cyclopentadienyl)niobium(V) Complexes and a Comparative DFT Study of the Bonding Capabilities of Diazabutadiene and Butadiene Ligands

The reactions of [NbCp′Cl2(Me3SiCCSiMe3)] (Cp′ = η5-C5H4SiMe3) with 2,3-dimethyl-1,4-diphenyl-1,4-diazabuta-1,3-diene (Me,Ph-DAD) and diketones R−CO−CO−R (R = Me, Ph) gave ene-diamido complexes [NbCp′Cl2(Me,Ph-DAD)] (1) and ene-diolato complexes [NbCp′Cl2{O(R)CC(R)O}] (R = Me, 2; Ph, 3), respectively, with simultaneous elimination of bis(trimethylsilyl)acetylene. The NMR spectroscopic data of these compounds are in agreement with a supine conformation, with respect to the Cp′ ring, of the ene-diamido and ene-diolato ligands. In order to gain further information concerning the bonding capabilities of the ene-diamido ligand, a DFT study of the model complex [NbCpCl2(HNCHCHNH)] (I) was performed. For comparison, a DFT analysis of the model compound [NbCpCl2(η4-CH2CHCHCH2)] (II) was also carried out. Differences in the bonding description of the diazabutadiene and butadiene ligands bonded to a common [NbCpCl2] moiety are discussed. A detailed analysis of the fragment orbital interactions in I provides no evidence for any positive overlap between the Nb centre and the inner carbon atoms of the DAD ligand. Dialkylation of the dichloro complex 1 gave dialkyl derivatives [NbCp′R2(Me,Ph-DAD)] (R = Me, 4; CH2SiMe3, 5; CH2C6H5, 6), for which the NMR spectroscopic data suggests a prone conformation of the DAD ligand. Treatment of the dimethyl derivative 4 with carbon monoxide and 2,6-dimethylphenyl isocyanide led to the formation of the oxa- and azaniobacyclopropane complexes [NbCp′{η2-(E)CMe2}(Me,Ph-DAD)] [E = O, 7; N(2,6-Me2C6H3), 8], respectively. Subsequent insertion of isocyanide into the Nb−C bond of 7 proceeds with formation of derivatives [NbCp′{η2-(O)CMe2-(CNAr)x}(Me,Ph-DAD)], (Ar = 2,6-Me2C6H3; x = 1, 9; 2, 10). All the complexes isolated were characterized by IR and NMR (1H, 13C{1H}) spectroscopy. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Theoretical study of the bonding capabilities of 1,4-diaza-1,3-butadiene and cis-1,3-butadiene ligands in cyclopentadienyl tantalum(V) complexes

A folded envelope geometry is generally encountered in structurally characterized high valent early transition metal compounds containing a substituted 1,4-diaza-1,3-butadiene ligand. In these cases the diazabutadiene ligand can be regarded as dianionic ene-diamido ligand and the folded five-membered ring can be described as a metallacyclo-2,5-diazapent-3-ene. A comparable metallacyclopent-3-ene description is attributed to η4-butadiene complexes of early transition metals, in which the ligand exhibits a σ2, π-character. For this reason, a parallel description was initially adopted by several authors for the ene-diamido ligands and the origin of the folding of the five-membered ring was attributed to the saturation of the metal center through the CC double bond. The aim of this paper is to discriminate the bonding capabilities of the 1,4-diaza-1,3-butadiene and cis-1,3-butadiene ligands on high-valent tantalum complexes, and to establish the origin of the folding of the 1,4-diaza-1,3-butadiene ligand. A Density Functional study (DFT) of the model complex [CpTaCl2(HNCHCHNH)] (1) and compound [CpTaCl2(η4-butadiene)] (2) has been carried out. The differences in the bonding description of these ligands coordinated to the identical [CpTaCl2] moiety are discussed through the examination of the HOMOs of 1 and 2 and on the basis of a FMO analysis. In complex 1, there is no evidence of any positive overlap between the tantalum center and the inner carbon atoms of the diazabutadiene ligand, while for 2 the classical σ2,π-description for the η4-butadiene ligand is well-founded. Consequently, the generally accepted bonding description of 1,4-diaza-1,3-butadiene ligands coordinated to high valent early transition complexes should be modified. The origin of the folding is the reorientation of the N hybrid orbitals with the purpose of saturating the metal center and no significant donation through the CC bond occurs.

Synthesis, molecular structure and properties of oxo-vanadium(IV) complexes containing the oxydiacetate ligand

The complex [V(O)(oda)(H2O)2] 1 [oda = O(CH2COO−)2] has been obtained by reaction of aqueous solutions of [V(O)(acac)2] with oxydiacetic acid. The coordination geometry around the vanadium in 1 is distorted octahedral with mutually trans water ligands and a planar conformation of the oda ligand (mer). The relative stability of the experimentally determined structure and that of the alternative isomer with a puckered oda conformation (fac) has been investigated by DFT calculations. The latter confirms that the mer geometry is more stable by 35.6 kJ mol−1. The complex [V(O)(oda)(μ-OMe)]2[Na(H2O)]22a is obtained by reaction of 1 with NaOH in methanol. The anions feature two V(O)(oda) units symmetrically bridged by methoxy groups in a syn-orthogonal arrangement, while the oda ligands have the fac conformation. Similar complexes [V(O)(oda)(μ-OMe)]2[K(H2O)]22b and [V(O)(oda)(μ-OMe)]2[HL]22c–2g are obtained from reaction with KOH or with selected N-donor bases (L), respectively. An excess of pyridine, however, causes the simple substitution of the water molecules in 1 and generates the monomer [V(O)(oda)(py)2] 3. Antiferromagnetic behaviour of binuclear compounds 2a, 2d and 2e is suggested by a variable-temperature study. Finally, the reaction of 1 with bidentate N-donor ligands allows the synthesis of the complexes [V(O)(oda)(N–N)]·H2O (N–N = 2,2′-bipyridine, 4; o-phenanthroline, 5). X-Ray characterization of 4 shows that the conformation of oda has changed from mer (as in the reactant 1) to fac.

Rhodium diphosphite pincer complexes. Rare preferred in-plane olefin conformation in square-planar compounds

Square-planar ethylene rhodium derivatives bearing pincer diphosphite ligands have been prepared and characterized, they display a rare in-plane coordination which, based on DFT calculations, has been mainly attributed to steric effects.

Theoretical analysis of bis(ethylene) complexes of molybdenum and tungsten

Abstract Density functional calculations on the zero-valent bis(ethylene) trans -[M(C 2 H 4 ) 2 (PH 3 ) 4 ] model complexes and the actual trans -[M(C 2 H 4 ) 2 (PMe 3 ) 4 ] (M=Mo, W) compounds were carried out at the BPW91 level of theory. The experimentally characterised molecular structures of both molybdenum and tungsten complexes were properly reproduced by the energy optimised geometries only when the trimethylphosphine ligands were used. The experimentally observed ruffling of the phosphine ligands was not detected when the simplified model was considered. This discrepancy was interpreted as a consequence of different steric interactions between the PH 3 and PMe 3 ligands. The theoretical analysis gives a good account of some chemical properties observed in these compounds. In particular, the low PMe 3 dissociation energies calculated for these compounds are in agreement with the experimental observation of free phosphine dissociation in the solutions of trans -[M(C 2 H 4 ) 2 (PMe 3 ) 4 ] compounds. The comparison of energy data for PH 3 and PMe 3 complexes corroborates the experimental hypothesis that phosphine dissociation has a steric origin.