Browsing by Author "Rojas, Rene S."

Now showing 1 - 10 of 10
  • No Thumbnail Available
    Item
    A new series of zirconium metallocenes derived from partially alkylated s-indacene with potential applications in the polymerization of ethylene
    (2015) Felipe Araneda, Juan; Morales-Verdejo, Cesar; Adams, Christopher; Martinez-Diaz, Ivan; Chavez, Ivonne; Teresa Garland, Maria; Rojas, Rene S.; Molins, Elies; Manuel Manriquez, Juan
    This contribution describes the synthesis and characterization of a series of zirconium metallocenes derived from partially alkylated s-indacene. The complexes [Cp*ZrCl2-s-Ic '' H] 1, [Cp/ZrCl2-s-Ic '' H] 3 and [CpZrCl2-s-Ic '' H] 4 (s-Ic'H = 2,6-diethyl-4,8-dimethyl-1-hydro-s-indacene; s-Ic '' H = 2,6-dibutyl-4,8-dimethyl-1-hydro-s-indacene) were synthesized from the monolithiated salts of s-indacene (s-Ic'H or s-Ic '' H) with one equivalent of C5R5ZrCl3 (R = H, CH3). All complexes here reported were characterized by means of H-1 and C-13 NMR, mass spectrometry, elemental analysis. Complexes [Cp*ZrCl2-s-Ic'H] 1 and [CpZrCl2-s-Ic'H] 2 (previously reported by NMR analysis) were characterized by X-ray diffraction. In order to gain further knowledge about their catalytic behavior, the complexes were tested in the catalysis of ethylene polymerization showing a highest activity. Complex 4 presents the highest ethylene polymerization activity than complexes 1 and 2, and 3 under the same working conditions. (C) 2015 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Approach to Circular Chemistry Preparing New Polyesters from Olive Oil
    (2023) Werlinger, Francisca; Caprile, Renato; Cardenas-Toledo, Valentino; Tarraff, Bastian; Mesias-Salazar, Angela; Rojas, Rene S.; Martinez, Javier; Trofymchuk, Oleksandra S.; Flores, Mario E.
    The transformation of cooking oils and their waste intopolyestersis a challenge for circular chemistry. Herein, we have used epoxidizedolive oil (EOO), obtained from cooking olive oil (COO), and variouscyclic anhydrides (such as phthalic anhydride PA, maleic anhydrideMA, and succinic anhydride SA) as raw materials for the preparationof new bio-based polyesters. For the synthesis of these materials,we have used the bis(guanidine) organocatalyst 1 andtetrabutylammonium iodide (Bu4NI) as cocatalyst. The optimalreaction conditions for the preparation of poly(EOO-co-PA) and poly(EOO-co-MA) were 80 degrees C for 5 husing toluene as solvent; however, the synthesis of poly(EOO-co-SA) required more extreme reaction conditions. Furthermore,we have exclusively succeeded in obtaining the trans isomer for MA-polyester.The obtained biopolyesters were characterized by NMR, Fourier transforminfrared, thermogravimetric analysis, and scanning electron microscopyanalyses. Since there are few examples of functionalized and definedcompounds based on olive oil, it is innovative and challenging totransform these natural-based compounds into products with high addedvalue.
  • No Thumbnail Available
    Item
    Bulky and Electron-Deficient α-Iminocarboxamidato-Nickel(II) Complexes: A Study of the Steric and Electronic Effects on Ethylene Activation
    (2021) Skarjan, Leon; Villegas-Escobar, Nery; Correa, Sebastian A.; Daniliuc, Constantin G.; Matute, Ricardo A.; Rojas, Rene S.
    Two alpha-iminocarboxamidato-nickel(II) complexes containing ligands with several CF3 groups were synthesized and characterized by NMR spectroscopy, elemental analysis, and density functional theory (DFT) calculations. Surprisingly, the prepared complexes were inactive toward ethylene oligo/polymerization reactions upon activation attempts with common lewis acid co-catalysts such as B(C6F5)(3) and BF3. Quantum chemistry calculations were employed to reveal that adduct formation is thermodynamically favored for small Lewis acids such as BF3 due to the sterically demanding ligand environment of the complex, confirming the experimental findings. DFT results associate the lack of polymerization activity with a highly unfavorable steric environment, undesirable London dispersion interactions between the ligands, and a strong electrostatic stabilization caused by the employed ligands. Our findings should help future researchers to identify necessary electronic and steric requirements for the compounds to generate active Ni(II) catalysts for ethylene oligo/polymerization activated by suitable boron Lewis acids.
  • No Thumbnail Available
    Item
    Highly Active CO2 Fixation into Cyclic Carbonates Catalyzed by Tetranuclear Aluminum Benzodiimidazole-Diylidene Adducts
    (2021) Mesias-Salazar, Angela; Yepes, Yersica Rios; Martinez, Javier; Rojas, Rene S.
    A set of tetranuclear alkyl aluminum adducts 1 and 2 supported by benzodiimidazole-diylidene ligands L-1, N,N'-(1,5-diisopropylbenzodiimidazole-2,6-diylidene)bis(propan-2-amine), and L-2, N,N'-(1,5-dicyclohexyl-benzodiimidazole-2,6-diylidene)dicyclohexanamine were synthetized in exceptional yields and characterized by spectroscopic methods. These compounds were studied as catalysts for cyclic carbonate formation (3a-o) from their corresponding terminal epoxides (2a-o) and carbon dioxide utilizing tetrabutylammonium iodide as a nucleophile in the absence of a solvent. The experiments were carried out at 70 degrees C and 1 bar CO2 pressure for 24 h and adduct 1 was the most efficient catalyst for the synthesis of a large variety of monosubstituted cyclic carbonates with excellent conversions and yields.
  • No Thumbnail Available
    Item
    Mono- and Dinuclear Asymmetric Aluminum Guanidinates for the Catalytic CO2 Fixation into Cyclic Carbonates
    (2021) Rios Yepes, Yersica; Mesias-Salazar, Angela; Becerra, Alexandra; Daniliuc, Constantin G.; Ramos, Alberto; Fernandez-Galan, Rafael; Rodriguez-Dieguez, Antonio; Antinolo, Antonio; Carrillo-Hermosilla, Fernando; Rojas, Rene S.
    A set of trisubstituted guanidine ligands L1H2-L4H2 with general formula (PrHN)(2)CNR (R = Ph (L1H2), R = 2,4,6-Me3C6H2(L2H2), R = p-BrC6H4(L3H2), R = (C5H4)Fe(C5H5), Fc (L4H2)) was employed to synthesize a family of mono- and dinuclear asymmetric methyl aluminum guanidinato compounds ((L2H)AlMe2 (1), (L4H)AlMe2 (2), (L-1)Al2Me4 (3), (L-2)Al2Me4 (4), (L-3)Al2Me4 (5), (L-4)Al2Me4 (6), (L1H)(2)AlMe (7), (L2H)(2)AlMe (8), and (L4H)(2)AlMe (9)) that were characterized by NMR spectroscopy (1-9) and single-crystal X-ray diffraction (4 and 8). These compounds were tested as catalysts for the fixation of carbon dioxide with epoxides to give cyclic carbonates, using tetrabutylammonium iodide (TBAI) as cocatalyst. The reactions were performed under solvent-free conditions at 70 degrees C and 1 bar CO2 pressure. Complexes 1-9 were more active than their respective free guanidines under the same experimental conditions for the synthesis of styrene carbonate (11a). The dinuclear complex 6 was the most efficient and active catalyst for the synthesis of several monosubstituted carbonates (11a-1) with excellent conversions and selectivities. Furthermore, the formation of some disubstituted cyclic carbonates (13a-c) using this dinuclear aluminum catalyst was also studied.
  • No Thumbnail Available
    Item
    Neutral and cationic methallyl nickel complexes in alkene activation: a combined DFT, ESI-MS and chemometric approach
    (2021) Trofymchuk, Oleksandra S.; Ortega, Daniela E.; Cortes-Arriagada, Diego; Pereira, Alfredo; Daniliuc, Constantin G.; Klitzke, Clecio F.; Santos, Leonardo S.; Rojas, Rene S.
    Herein, we report a comparative study of ethylene activation and 1-hexene isomerization carried out with isomeric neutral and cationic methallyl nickel complexes L1Ni(eta(3)-C3H5) and [L1Ni(eta(3)-C3H5)][B(Ar-F)(4)] in the presence of borane co-catalysts. To understand the reactivity of the nickel complexes with NacNac ligands, we used chemometric methods to classify different catalysts reported to date. The mechanism of the interaction of [L1Ni(eta(3)-C3H5)][B(Ar-F)(4)]/B(C6F5)(3) with 1-hexene was studied by ESI-MS which allowed the detection of cationic species formed in situ. Moreover, there is a very small difference in reactivities from combination of nickel complexes and borane co-catalysts used for alkene isomerization, while the reactivity with ethylene of both systems is very different; [L1Ni(eta(3)-C3H5)][B(Ar-F)(4)]/B(C6F5)(3) produces butene, while L1Ni(eta(3)-C3H5)/B(C6F5)(3) forms polyethylene. Furthermore, DFT studies revealed that the origin of the catalytic activity in the cationic and neutral methallyl nickel complexes co-activated by B(C6F5)(3) is mainly from direct steric effects of the ligand-nickel center where the conformation of the chelate ring is affected by the catalyst symmetry. This work demonstrates how the cationic or neutral nature of the same system affects its catalytic and structural properties.
  • No Thumbnail Available
    Item
    Nickel alpha-Keto-beta-Diimine Initiators for Olefin Polymerization
    (WILEY-V C H VERLAG GMBH, 2009) Azoulay, Jason D.; Rojas, Rene S.; Serrano, Abigail V.; Ohtaki, Hisashi; Galland, Griselda B.; Wu, Guang; Bazan, Guillermo C.
    (Figure Presented) A new ligand-metal combination (see picture, Ni green, Br brown, N blue, O red, C gray) was designed to be cationic and to benefit from removal of electron density by the action of a Lewis acid on the ligand framework. In the presence of various activators, the resulting catalytic site is highly active for ethylene polymerization and capable of polymerizing α-olefins to high molecular weights. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
  • No Thumbnail Available
    Item
    PALLADIUM COMPLEX BEARING 3,5-BIS(BENZOTRIAZOL-1-YLMETHYL) TOLUENE LIGAND CATALYZES OXIDATIVE AMINATION OF ALLYL BUTYL ETHER
    (2013) Hurtado, John; Rojas, Rene S.; Perez, Edwin G.; Valderrama, Mauricio
    The reaction of 3,5-bis(bromomethyl)toluene with benzotriazole yields the bidentate ligand 3,5-bis(benzotriazol-1-ylmethyl)toluene (1). This ligand reacts with [PdCl2(cod)] (cod = 1,5-cyclooctadiene) to give the complex [PdCl2{3,5-bis(benzotriazol-1-ylmethyl)tolyl}] (2). These compounds were characterized by elemental analyses, mass spectra, and FTIR and NMR (H-1, C-13) spectroscopies. The palladium(II) complex 2 shows high activity as catalyst for oxidative amination, involving allyl butyl ether and phthalimide as substrates and PhICl2 as a stoichiometric oxidant.
  • No Thumbnail Available
    Item
    Synthesis and structures of N-arylcyano-β-diketiminate zinc complexes and adducts and their application in ring-opening polymerization of L-lactide
    (2015) Trofymchuk, Oleksandra S.; Daniliuc, Constantin G.; Kehr, Gerald; Erker, Gerhard; Rojas, Rene S.
    Zinc amide complexes ZnL1N( SiMe3) 2, ZnL2N( SiMe3) 2 ( 1 and 2), their tris( pentafluorophenyl) borane adducts ZnL1N( SiMe3) 2$ B( C6F5) 3 ( 3), ZnL2N( SiMe3) 2$ 2B( C6F5) 3 ( 4), pentafluorophenyl zinc complex ZnL1C6F5 ( 5) and its adduct ZnL1C6F5$ B( C6F5) ( 6) supported by N- arylcyano- b- diketiminate ligands, as well as bis- ligated Zn( L2) 2 ( 7) were synthesized and characterized by NMR, IR, elemental analysis and X- ray diffraction. Zinc crystal structures of 1, 4, and 7 showed mononuclear complexes, while 2 and 5 were dimmers. ROP of L- lactide with zinc complexes and their B( C6F5) 3 adducts leads to generation of poly( L- LA) with high molecular weight and relatively narrow molecular weight distribution. The monomer conversion reached completion in 40 min only for zinc amide complex 1, while for other compounds it was necessary to use at least 5 hours to achieve significant polymerization yields. Coordination of the B( C6F5) 3 molecule close to the metal center blocks L- lactide insertion and thus decreases the activity of respective adducts in comparison with borane- free zinc complexes.
  • No Thumbnail Available
    Item
    Toward a Neutral Single-Component Amidinate Iodide Aluminum Catalyst for the CO2 Fixation into Cyclic Carbonates
    (2021) Saltarini, Sebastian; Villegas-Escobar, Nery; Martinez, Javier; Daniliuc, Constantin G.; Matute, Ricardo A.; Gade, Lutz H.; Rojas, Rene S.
    A new iodide aluminum complex ({AlI(kappa(4)-naphbam)}, 3) supported by a tetradentate amidinate ligand derived from a naphthalene-1,8-bisamidine precursor (naphbamH, 1) was obtained in quantitative yield via reaction of the corresponding methyl aluminum complex ({AlMe(kappa(4)-naphbam)}, 2) with 1 equiv of I-2 in CH2Cl2 at room temperature. Complexes 2 and 3 were tested and found to be active as catalysts for the cyclic carbonate formation from epoxides at 80 degrees C and 1 bar of CO2 pressure. A first series of experiments were carried out with 1.5 mol % of the alkyl complex 2 and 1.5 mol % of tetrabutylammonium iodide (TBAI) as a cocatalyst; subsequently, the reactions were carried out with 1.5 mol % of iodide complex 3 as a single-component catalyst. Compound 3 is one of the first examples of a nonzwitterionic halide single-component aluminum catalyst producing cyclic carbonates. The full catalytic cycle with characterization of all minima and transition states was characterized by quantum chemistry calculations (QCCs) using density functional theory. QCCs on the reaction mechanism support a reaction pathway based on the exchange of the iodine contained in the catalyst by 1 equiv of epoxide, with subsequent attack of I- to the epoxide moiety producing the ring opening of the epoxide. QCCs triggered new insights for the design of more active halide catalysts in future explorations of the field.