Abstract

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 R-hydride elimination is kinetically favored, but 1-butene decoordination is highly endergonic (Delta G degrees = 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 (Delta G degrees = 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 (delta G = 22.4 kcal/mol, TOF = 2.5 x 10-4 s-1) compared to the 2-butene cycle (delta G = 36.8 kcal/mol, TOF = 6.3 x 10-15 s-1). Here, delta G 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 delta G value for 1-butene formation indicates a kinetically more favorable pathway, while the higher delta G 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.