Isolation and Characterization of a Class II Mixed-Valence Chromium(I)/(II) Self-Activating Ethylene Trimerization Catalyst

Reduction of the tetranuclear {[(t-Bu)NPPh2]-Cr[μ-(t-Bu)NPPh2]2Cr}2(μ-Cl)2 (1) with either KC8 or vinyl Grignard afforded the dinuclear, mixed-valence (Me3P)Cr[μ-(t-Bu)NPPh2]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, {[(η4-butadiene)Cr (μ,η4-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.