Abstract
Reaction of RN(H)PBr(Ph)(2)N(H)R [R = t-Bu, i-Pr, Ph] with two equivalents of n-BuLi followed by reaction with CrCl2(THF)(2) afforded the divalent chromium complexes [(t-Bu)NP(Ph)(2)-N(t-Bu)]Cr(mu(2)-Cl)(2)Li(THF)(2) (1), (i-Pr)NP(Ph)(2)N(i-Pr)]Cr(mu(2)-Cl)(2)Li(THF)(2) (2), and [{[(Ph)-NP(Ph)(2)N(Ph)]Cr}(2)(mu(2)-Cl)(3)][Li(DME)(3)] (3). The trivalent analogue of 1, {[(t-Bu)NP(Ph)(2)-N-(t-Bu)]Cr(mu(2)-Cl)(3)(mu(2)-Cl)(2)}{Li (THF)(2)} (4), was :obtained in a similar rnahner via treatment of the double deprotonated ligand with CrC13(THP)3. Both-reactions of the -divalent Lortriva/ent 4 with AlMe3 yielded the trivalent and {[(t-Bu)NP(Ph)(2)N(t-Bu)](2)Cr}{Me3Al)(2)Cl)}center dot toluene (5) Upon activation With MAO 1-3 produced produced unprecedented and potentially; useful catalytic systems for nonselective ethylene oligomerization devoid of polymer. Divalent clearly the species responsible for the catalytic behavior, ruling out that nonselective oligomerization proceeds via a redox metallacycle mechanism. The absence of polymer in combination with the record activity makes 1 competitive with the best performing industrially used systems.