Mechanistic Studies on Selective Trimerization of Linear α-Olefins over a Supported Titanium Catalyst

Abstract

The supported titanium catalyst s(FI)Ti, generated by adding (FI)TiCl 3 to MAO-treated SiO 2 (FI = (N-(5-methyl-3-(1-adamantyl)salicylidene)-2'-(2"-methoxyphenyl)anilinato)], effects the selective trimerization of the linear α-olefins (LAOs) propene, 1-pentene, 1-hexene, 1-decene, with >95% selectivity for trimers and ~85% selectivity to a single isomer thereof (2,3,5-trialkyl-1-hexene). Mechanistic interpretations are offered for the high regioselectivity as well as for some unusual kinetics behavior, including third-order dependence on LAO concentration and nearly identical initial rates at 0 and 25 °C.

Synthesis of L2Ni(ORF)2 (RF = C(CF3)3) Complexes and Their Reactivity in Ethylene Oligomerization

“…Up to now, the limited selectivity observed with nickel-based catalysts is mainly rationalized through a Cossee–Arlman mechanism with the active species featuring a Ni–H or Ni–C bond. , Nonetheless, only few nickel catalysts have been reported to be highly selective in ethylene dimerization to butenes/1-butene. − In these cases, the precise mechanism has not been studied, yet, in general, catalysts that follow a metallacyclic mechanism are known to be much more selective toward a unique 1-alkene. − Moreover, it has been shown that nickel was able, with activated alkenes such as tetrafluoroethylene (TFE), norbornadiene, or dimethylcyclopropene, to achieve an oxidative coupling to reach metallacyclic complexes (Scheme , top). − In addition, Grubbs showed that butenes can be obtained from a mixture of (Cy 3 P) 2 NiCl 2 and 1,4-dilithiobutane, through the proposed decomposition of the nickellacyclopentane . Binger reported one year after that an isolated nickellacycle yielded 1-butene upon heating at 165 °C (Scheme , bottom) …”

Alkene oligomerization via metallacycles: Recent advances and mechanistic insights

“…Bercaw and co-workers also demonstrated that [(FI)Ti IV Me 2 ] + could trimerize selectively a range of LAOs (propene to 1-decene) following the metallacycle pathway. [34] Indeed, trimers are formed in >95% among which 2,3,5-trialkyl-1-hexene are obtained with a selectivity of ca 85% of the overall products. The high selectivity is explained by an oxidative coupling of two LAOs in the most sterically favorable manner, followed by the sterically appropriate insertion of a new LAO in the previously obtained titanacyclopentane.…”

Titanium-based phenoxy-imine catalyst for selective ethylene trimerization: effect of temperature on the activity, selectivity and properties of polymeric side products

“…Most of the reported literature on titanium-based trimerization systems focused on improving and rationalizing the oligomerization reaction, paying little attention to polymerization. [8][9][10][11][12][13][14][15][16][17][18][19][20] On the one hand, applying the ligandoriented catalyst design strategy, Fujita and coworkers reported the strong dependence between ligand structure and the reactivity of trimerization phenoxy-imine systems. 9 Indeed, 1hexene selectivity and activity can be tuned by subtle changes of substituents on specific positions of the phenyl rings.…”