| Abstrakt: |
The Cossee–Arlman mechanism of nickel-catalyzed oligomerization and dimerization with various N∩N-type ligands was studied using the DFT method. For the L1 ligands (L1 = 2,9-disubstituted 1,10-phenanthroline), the dimerization energy barriers for R = Me and R = Ph are about 17.9 and 15.8 kcal mol−1, respectively. However, the presence of Ph substituents at positions 2 and 9 of the L1 ligand reduces the free energy barriers for the dimerization and trimerization processes by approximately 2.1 and 8.1 kcal mol−1, respectively. Therefore, the Ph substituents prevent the removal of β-H from 1-butene, thus promoting the formation of 1-hexene. This result is consistent with experimental observations. In the case of the L2 ligands (L2 = substituted 2-benzoxazole-pyridines) with R1 = H and R2 = H or Me, and R3 = H, the calculated dimerization energy barriers for the systems (H-H) and (H-Me) are about 12.8 and 20.5 kcal mol−1, respectively. The energy barrier for the system with R1 = H and R2 = R3 = Me (Me-Me) is about 20.9 kcal mol−1. Thus, the activity of these systems towards the formation of 1-butene can be arranged as (H-H) > (H-Me) > (Me-Me). As for L3 ligands (L3 = 2-benzimidazolylpyridine derivatives), six systems with R1 = H, Me, tBu; R2 = H, Me, were studied. The calculated dimerization energy barrier values indicate that the (H-H), (H-Me), and (H-tBu) systems (10.8, 11.1, and 10.9 kcal mol−1, respectively) are more active than the (Me-H), (Me-Me) and (Me-tBu) systems (18.8, 19.1 and 19.0 kcal mol−1, respectively). Finally, for the L4 ligand (L4 = 2-benzoimidazol-8-alkylquinoline derivatives), nine systems were studied, divided into three groups: A system (R1 = H and R2 = H or Me or Et), B system R1 = Me with identical R2 substituents, and C system (R1 = Et with identical R2 substituents). Based on the values of the calculated energy barriers for dimerization and trimerization, the B system shows higher activity than the other systems. [ABSTRACT FROM AUTHOR] |
