Isolation and characterization of a class II mixed-valence chromium(I)/(II) self-activating ethylene trimerization catalyst

Abstract

Reduction of the tetranuclear {[(t-Bu)NPPh 2]-Cr[μ-(t-Bu) NPPh 2] 2Cr} 2(μ-Cl) 2 (1) with either KC 8 or vinyl Grignard afforded the dinuclear, mixed-valence (Me 3P)Cr[μ-(t-Bu)NPPh 2] 3Cr (2) with the two metals possessing distinctively different coordination environments. According to the formulation of 2 as Cr(I)/Cr(II) mixed-valence species, 2 acts as a self-activating catalyst, producing under pressure of ethylene a mixture of 1-butene and 1-hexene. Activation with three different activators selectively produced three different products, namely, 1-butene with TEAL, 1-hexene with DMAO/TEAL, and LAO-free highly linear HMWPE with DMAO. Mixtures of 1-hexene and 1-butene were also obtained upon activation with vinyl Grignard. In this case it was possible to isolate, albeit in very low yield, an intriguing butadiene/butadiene-diyl cluster, {[(ν 4-butadiene)Cr (μ,ν 4-butadienediyl)(μ- NP)Mg] 2(μ-Cl) 4Mg(THF) 2}{[(THF) 3Mg] 2(μ-Cl) 3} 2 (3), which is also a highly selective self-activating trimerization catalyst. © 2011 American Chemical Society.