Ligand-Induced Product Switching between 4‑Methyl-1-pentene and 2‑Methyl-1-pentene in Bis(imino)pyridine/V(III)-Catalyzed Propylene Dimerization: Cossee–Arlman Versus Metallacycle Mechanism

Ligand-induced
product switching between 4-methyl-1-pentene (4M1P)
and 2-methyl-1-pentene (2M1P) for propylene dimerization with a bis­(imino)­pyridine
vanadium­(III) catalytic system was investigated using the combined
density functional theory and DLPNO-CCSD­(T) method to determine which
mechanism (metallacycle vs Cossee–Arlman)
is most likely to be present. The calculations show that the Cossee–Arlman
mechanism has low rate-determining energy barriers in comparison to
the metallacycle mechanism. The NBO charge analysis supports that
the electron-withdrawing/pushing substituents influence the process
of the first propylene insertion, while the steric position of the
ligand and vanadium affects the process of the second propylene insertion.
The different substituents introduced to the backbone of the ligand
changed the rate-determining step, which induced the switchable selectivity
between 4M1P and 2M1P.

本研究针对双(亚胺)吡啶(bis(imino)pyridine)三价钒(vanadium(III))催化体系下的丙烯二聚反应展开系统探究，聚焦配体诱导的4-甲基-1-戊烯(4-methyl-1-pentene, 4M1P)与2-甲基-1-戊烯(2-methyl-1-pentene, 2M1P)间的产物选择性切换行为。本研究通过结合密度泛函理论(Density Functional Theory, DFT)与DLPNO-CCSD(T)计算方法，旨在明确该反应最可能遵循的反应机理为金属环机理(metallacycle mechanism)还是科斯-阿尔曼机理(Cossee–Arlman mechanism)。计算结果表明，相较于金属环机理，科斯-阿尔曼机理的决速能垒更低。自然键轨道(Natural Bond Orbital, NBO)电荷分析证实，吸电子/给电子取代基会对首次丙烯插入步骤产生调控作用，而配体与钒中心的空间位阻则会影响第二次丙烯插入过程。在配体骨架上引入不同取代基可改变反应的决速步骤，进而实现4M1P与2M1P之间的选择性切换。