Ti-Catalyzed Selective Isomerization of Terminal Mono-substituted Olefins

Abstract

Transition metal complexes have been utilized in the homogeneous catalysis because of selectivity and catalytic activity under mild conditions. The isomerization of olefins catalyzed by transition metal complexes constitutes one of important type of reaction in organometallic chemistry. The isomerization of olefins occurs either by a metal hydride addition-elimination or by a π-allyl metal hydride intermediate. HCo(CO)4, [(C2H4)2RhCl]2, Ni[P(OEt)3]4, and PtCl2(PPh3)2-SnCl2 are effective catalysts for isomerization of olefins via a metal hydride addition-elimination mechanism, and Fe3(CO)12 catalyzed isomerization of 3-ethyl-1pentene and isomerization of 1-heptene catalyzed by (PhCN)2PdCl2 occur via a π-allyl metal hydride mechanism. The cis/trans ratio of 2-butene obtained from isomerization of 1-butene by RhH(CO)(PPh3)3 has also been investigated. The skeletal isomerization of olefins catalyzed by (R3P)2NiCl2 is developed such as conversion of cis-1,4hexadiene to trans-2-methyl-1,3-pentadiene. Titanium complexes serve as an effective catalysts for a variety of reactions such as hydroalumination, hydroboration, and hydrogenation of unsaturated hydrocarbons. We have been interested in the selective reactions of unsaturated hydrocarbons by using titanium and zirconium compounds. The reagent system composed of LiAlH4/Cp2TiCl2 ≤ 2 in the molar ratio promotes the isomerization of 1-octene, but the detailed reaction for isomerization of olefins has not been reported. We report here a selective isomerization of olefins with low valent titanium complex generated from Cp2TiCl2 (Cp=cyclopentadienyl) and LiAlH4.