Iñaki Silanes

Publications (5)12.16 Total impact

• Article: Comparison of Ti, Zr, and Hf as Cations for Metallocene-Catalyzed Olefin Polymerization

  Iñaki Silanes, Jose M. Mercero, Jesus M. Ugalde
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  ABSTRACT: In this paper we make use of a carefully chosen counterion model, B(CF2Cl)3, for a molecularly well-defined metallocenic catalyst counterion, B(C6F5)3, to perform a comparison of Cp2M(CH3)2-type metallocene activities toward ethylene polymerization, for M = Ti, Zr, and Hf. Monomer complexation and chain-insertion barriers are calculated and discussed, and a higher intrinsic activity for titanium is derived. Calculations are also performed in order to add further evidence of the suitability of the counterion model used. We conclude that the model employed here can act as an accurate enough substitute for the original borate in quantum mechanical calculations.
  08/2006;
• Article: A joint experimental and theoretical study of cation-pi interactions: multiple-decker sandwich complexes of ferrocene with alkali metal ions (Li+, Na+, K+, Rb+, Cs+).

  Alireza Haghiri Ilkhechi, Jose M Mercero, Iñaki Silanes, Michael Bolte, Matthias Scheibitz, Hans-Wolfram Lerner, Jesus M Ugalde, Matthias Wagner
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  ABSTRACT: A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.
  Journal of the American Chemical Society 09/2005; 127(30):10656-66. · 9.91 Impact Factor
• Article: Comparative Study of Various Mechanisms for Metallocene-Catalyzed α-Olefin Polymerization

  Iñaki Silanes, Jesus M. Ugalde
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  ABSTRACT: In this paper we try to give answers to some unexplained flaws in the widely accepted Cossée−Arlman mechanism (CAM) for the propagation step of the polymerization of α-olefins. We first take the bare cationic catalyst and make a comparison of the CAM with the so-called Trigger mechanism (TM) proposed by Ystenes, and not only see whether the latter model can predict, qualitatively, some reaction behaviors not explained by the former one but also theoretically calculate both reaction paths and make a quantitative comparison, in terms of reaction free energy. It turns out that, while in terms of electronic energy the TM is favored, inclusion of free energy corrections gives a lower energy profile for the CAM reaction path. We then make use of a model for an experimentally used catalyst counterion and study how it affects the reactivity of the metallocenic cation fragment toward the monomer.
  05/2005;
• Article: Atomic charge states in a weakly coupled plasma environment.

  Iñaki Silanes, Jose M Mercero, Jesus M Ugalde
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  ABSTRACT: The relative stability of various charge states of a number of selected elements has been studied as a function of increasing screening due to a weakly bound plasma represented by the statically screened Coulomb potential of the Yukawa-type. Elements with positive electron affinity in a vacuum are predicted to undergo a sequential electron detachment process from anionic state to the cationic one as the inverse screening length of plasma increases. Conversely, elements with negative electron affinity in a vacuum present only two charge states, neutral and positive. At small screening the neutral is the most stable charge state, and as the screening increases the cation develops as the most stable charge state. Values of the inverse screening length for each of the transitions have been calculated and discussed.
  Physical Review E 09/2002; 66(2 Pt 2):026408. · 2.26 Impact Factor
• Article: Reactivity of Co+(3F,5F), Ni+(2D,4F), and Cu+(1S,3D): Reaction of Co+, Ni+, and Cu+ with Water

  Arantxa Irigoras, Oihana Elizalde, Iñaki Silanes, Joseph E. Fowler, Jesus M. Ugalde
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  ABSTRACT: In this paper we conclude the study of the reaction of water with the first row transition metal ions. We report the study of the reaction of water with the late (Co+, Ni+, and Cu+) first row transition metal cations in both high- and low-spin states. In agreement with experimental observations, no exothermic products are found and the oxides are predicted to be more reactive than the metal ions. Formation of endothermic products is examined. An in-depth analysis of the reaction paths possible for these reactions is given, including various minima and several important transition states. All results have been compared with existing experimental and theoretical data, and our earlier works covering the (Sc+-Fe+) + H2O reactions to observe existent trends for the first row transition metal ions.
  12/1999;