Browsing by Author "Rojas, René S."

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    Aminoquinoline derivative nickel phosphine complex for ethylene dimerization: A computational and experimental approach
    (2025) Trofymchuk, Oleksandra S.; Ortega, Daniela E.; Alan Raúl, Cabrera Caballero; Daniliuc, Constantin G.; Rojas, René S.
    In this study, we report the synthesis and characterization of a novel nickel complex derived from an aminoquinoline derivative formed during its reaction with Ni(PPh₃)₂ClPh in the presence of potassium hydride under heating. Notably, the resulting nickel complex (precatalyst 2) exhibits catalytic activity toward ethylene activation in the presence of five equivalents of B(C₆F₅)₃, promoting ethylene oligomerization. This study highlights the potential of this new nickel system for selective olefin transformations. Density Functional Theory (DFT) calculations indicate that β-hydride elimination is kinetically favored, but 1-butene decoordination is highly endergonic (ΔG ◦ = 21.6 kcal/mol), making it slow under catalytic conditions. However, in the presence of ethylene significantly lowers this energy to 4.1 kcal/mol, facilitating product release. In contrast, 2-butene decoordination is significantly less endergonic (ΔG ◦ = 4.5 kcal/mol), implying a higher selectivity for 2-butene formation. Despite this, the catalytic cycle for 1-butene formation exhibits significantly higher activity (δG = 22.4 kcal/mol, TOF = 2.5 × 10⁻⁴ s⁻¹) compared to the 2-butene cycle (δG = 36.8 kcal/mol, TOF = 6.3 × 10⁻¹⁵ s⁻¹). Here, δG represents the energetic span of the catalytic cycle, which accounts for the difference between the highest energy transition state and the most stable intermediate within the cycle, directly correlating with the turnover frequency (TOF). The lower δG value for 1-butene formation indicates a kinetically more favorable pathway, while the higher δG for 2-butene formation suggests a slower overall rate despite its thermodynamic preference. These findings provide valuable insights into the reactivity and selectivity of nickel-mediated olefin oligomerization, offering a deeper mechanistic understanding of transition-metal-catalyzed transformations.
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    New Aluminum Complexes with an Asymmetric Amidine–Imine Ligand: Synthesis, Characterization, and Application in Catalysis
    Gómez Zamorano, Fernando; Rojas Moraga, María José; Mallet-Ladeira, Sonia; Cabrera, Alan R.; Garo, Jordan; Sotiropoulos, Jean-Marc; Maerten, Eddy; Madec, David; Rojas, René S.
    In this work, a new asymmetric amidine–imine ligand, using 1,8-diaminonaphthalene as a rigid platform, was synthesized and characterized, and its ability to form complexes with aluminum(III) was investigated. Several aluminum complexes were synthesized and characterized in solution and in the solid state. The synthesis of a dihalogenated aluminum(III) complex (AlI2L) using a reducing agent revealed an atypical pathway, which was investigated using Density Functional Theory (DFT). The dimethylated aluminum complex AlMe2L and the dihalogenated aluminum complex AlI2L were evaluated as catalysts for the transformation of CO2 and epoxides into cyclic carbonates in the presence of Bu4NI as a co-catalyst or in a single-component system, respectively. AlMe2L/Bu4NI appeared to be the most efficient system under 1 bar of CO2 at 90 °C.