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Feliu Maseras

Publications and source records attributed to Feliu Maseras.

9 recordsLinked to original sources
PubMed2003

Influence of media and homoconjugate pairing on transition metal hydride protonation. An IR and DFT study on proton transfer to CpRuH(CO)(PCy3).

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy(3)) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF(3))(3)COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (eta(2)-H(2))-complex 3 (DeltaH() = 11.0 +/- 0.5 kcal/mol and DeltaS() = -19 +/- 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF(3)COOH and (CF(3))(3)COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR](-) in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy(3))(eta(2)-H(2))](+) is driven by the formation of the homoconjugated anionic complex [ROHOR](-). Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy(3)), observed at temperatures above 250 K.

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PubMed2003

An oscillating C2(2-) unit inside a copper rectangle.

[Cu4(mu-dppm)4(mu4-eta1,eta2-C[triple bond]C-)]2+ has been shown by 31P and 1H NMR studies to undergo two fluxional processes in solution, the oscillation of the C[triple bond]C2- unit inside the copper rectangle and the flipping of the diphosphines, and this has been supported by DFT(B3LYP) calculations.

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PubMed2003

Density functional study on the mechanism of the vanadium-catalyzed oxidation of sulfides by hydrogen peroxide.

A computational study with the Becke3LYP method is carried out on the mechanism of the reaction of complexes V(O)(L)(OOH) and V(O)(LH)(OO) (L = O(CH)(3)N(CH(2))(2)O) with CH(3)S-SCH(3), a system that stands as a model for experimental systems where the metal complex contains larger chelating Schiff bases and the substrate is bis(tert-butyl) disulfide. The different possible isomers of both the hydroperoxo V(O)(L)(OOH) and the peroxo V(O)(LH)(OO) forms of the catalyst are explored, and the reactivity of the most stable among them with the dimethyl disulfide substrate is studied through location of the corresponding transition states. A large variety of reactive paths happen to exist, though in all cases the reaction takes place through a direct transfer process, with the simultaneous formation of the S-O bond and breaking of the O-O bond being the rate-limiting step.

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PubMed2002

Silyl, hydrido-silylene, or other bonding modes: some unusual structures of [(dhpe)Pt(SiHR2)]+ (dhpe = H2P-CH2-CH2-PH2; R = H, Me, SiH3, Cl, OMe, NMe2) and [(dhpe)Pt(SiR3)](+) (R = Me, Cl) from DFT calculations.

DFT (B3LYP) calculations have been carried out in order to quantitatively evaluate the energies and stereochemistry of the accessible structures of [(dhpe)Pt(SiHR(2))](+) (dhpe = H(2)P-CH(2)-CH(2)-PH(2); R = H, CH(3), SiH(3), Cl, OMe, SMe, NMe(2)) and of [(dhpe)Pt(SiR(3))](+) (R = CH(3), Cl). A number of different isomers have been located. The expected terminal silyl or hydrido-silylene complexes are often not the most stable complexes. An isomer in which an H or an R group bridges a Pt=SiHR or Pt=SiR(2) bond is found to compete with the terminal silyl or hydrido-silylene isomers. In some cases, isomers derived from cleavage of a C-H bond and formation of a silene or disilene ligand are obtained. The structures of the platinum silyls differ from that of the equivalent alkyl complex, calculated for [(dhpe)Pt(CH(3))](+).

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PubMed1999

Thermally Activated Site Exchange and Quantum Exchange Coupling Processes in Unsymmetrical Trihydride Osmium Compounds.

Reaction of the hexahydride complex OsH(6)(P(i)Pr(3))(2) (1) with pyridine-2-thiol leads to the trihydride derivative OsH(3){kappa-N,kappa-S-(2-Spy)}(P(i)Pr(3))(2) (2). The structure of 2 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted pentagonal bipyramid with the phosphine ligands occupying axial positions. The equatorial plane contains the pyridine-2-thiolato group, attached through a bite angle of 65.7(1) degrees, and the three hydride ligands. The theoretical structure determination of the model complex OsH(3){kappa-N,kappa-S-(2-Spy)}(PH(3))(2) (2a) reveals that the hydride ligands form a triangle with sides of 1.623, 1.714, and 2.873 Å, respectively. A topological analysis of the electron density of 2a indicates that there is no significant electron density connecting the hydrogen atoms of the OsH(3) unit. In solution, the hydride ligands of 2 undergo two different thermally activated site exchange processes, which involve the central hydride with each hydride ligand situated close to the donor atoms of the chelate group. The activation barriers of both processes are similar. Theoretical calculations suggest that the transition states have a cis-hydride-dihydrogen nature. In addition to the thermally activated exchange processes, complex 2 shows quantum exchange coupling between the central hydride and the one situated close to the sulfur atom of the pyridine-2-thiolato group. The reactions of 1 with L-valine and 2-hydroxypyridine afford OsH(3){kappa-N,kappa-O-OC(O)CH[CH(CH(3))(2)]NH(2)}(P(i)Pr(3))(2) (3) and OsH(3){kappa-N,kappa-O-(2-Opy)}(P(i)Pr(3))(2) (4) respectively, which according to their spectroscopic data have a similar structure to that of 2. In solution, the hydride ligands of 3 and 4 also undergo two different thermally activated site exchange processes. However, they do not show quantum exchange coupling. The tetranuclear complexes [(P(i)Pr(3))(2)H(3)Os(&mgr;-biim)M(TFB)](2) [M = Rh (5), Ir (6); H(2)biim = 2, 2'-biimidazole; TFB = tetrafluorobenzobarrelene] have been prepared by reaction of OsH(3)(Hbiim)(P(i)Pr(3))(2) with the dimers [M(&mgr;-OMe)(TFB)](2) (M = Rh, Ir). In solution the hydride ligands of these complexes, which form two chemically equivalent unsymmetrical OsH(3) units, undergo two thermally activated site exchanges and show two different quantum exchange coupling processes.

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PubMed1996

Theoretical Evaluation of Steric Effects in [ReH(5)(PR(3))(2)(SiR(3))(2)] Complexes with the IMOMM Method.

A theoretical study including full geometry optimizations is carried out at the IMOMM(MP2:MM3) (IMOMM = integrated molecular orbital molecular mechanics) computational level on the [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] systems, the results being compared with available experimental diffraction data, as well as with MP2 results on the model system [ReH(5)(PH(3))(2)(SiH(3))(2)]. A simple scheme for the analysis of the relative weight of different contributions to the "steric" distortion is also proposed and applied to the same [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] species.

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PubMed1996

Oxidative Addition of Group 14 Element Hydrido Compounds to OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2): Synthesis and Characterization of the First Trihydrido-Silyl, Trihydrido-Germyl, and Trihydrido-Stannyl Derivatives of Osmium(IV).

The dihydrido-olefin complex OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2) (2) reacts with H(2)SiPh(2) to give OsH(3)(SiHPh(2))(CO)(P(i)Pr(3))(2) (3). The molecular structure of 3 has been determined by X-ray diffraction (monoclinic, space group P2(1)/c with a = 16.375(2) Å, b = 11.670(1) Å, c =18.806(2) Å, beta = 107.67(1) degrees, and Z = 4) together with ab initio calculations on the model compound OsH(3)(SiH(3))(CO)(PH(3))(2). The coordination geometry around the osmium center can be rationalized as a heavily distorted pentagonal bipyramid with one hydrido ligand and the carbonyl group in the axial positions. The two other hydrido ligands lie in the equatorial plane, one between the phosphine ligands and the other between the SiHPh(2) group and one of the phosphine ligands. Complex 3 can also be prepared by reaction of OsH(eta(2)-H(2)BH(2))(CO)(P(i)Pr(3))(2) (4) with H(2)SiPh(2). Similarly, the treatment of 4 with HSiPh(3) affords OsH(3)(SiPh(3))(CO)(P(i)Pr(3))(2) (5), while the addition of H(3)SiPh to 4 in methanol yields OsH(3){Si(OMe)(2)Ph}(CO)(P(i)Pr(3))(2) (6). Complex 2 also reacts with HGeR(3) and HSnR(3) to give OsH(3)(GeR(3))(CO)(P(i)Pr(3))(2) (GeR(3) = GeHPh(2) (7), GePh(3) (8), GeEt(3) (9)) and OsH(3)(SnR(3))(CO)(P(i)Pr(3))(2) (R = Ph (10), (n)Bu (11)), respectively. In solution, compounds 3 and 5-11 are fluxional and display similar (1)H and (31)P{(1)H} NMR spectra, suggesting that they possess a similar arrangement of ligands around the osmium atom.

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