Crystallographic Revelation of the Role of AlMe₃ (in MAO) in Cr [NNN] Pyrazolyl Catalyzed Ethylene Trimerization

A series of Cr−Al intermetallic complexes, viz. [(Pz′3CH)2CrII2(μ-Cl)2]2+·2[(Me2XAl)(μ-Cl)(Me2XAl)]− (X = Me/Cl), Pz′3CHCrIIIMeCl(μ-Cl)(AlMe2X) (X = Me/Cl), and Pz′2CHCH2(μ-N)CH2(μ-Ph)CrIIICl(μ-Cl)AlMe2, have been isolated from the reactions of CrCl3(NNN) (NNN = tridentate pyrazolyl ligand) with neat AlMe3 or commercial MAO solutions. The products generally show high activity and selectivity in ethylene trimerization. Crystallographic analysis has provided structural evidence for Cr(III) reduction by residual AlMe3 in a mixture containing the “real” activator (MAO) as well as other transformations: viz., adduct formation, methylation, cationization, halide abstraction, N−H deprotonation, and C−H cleavage of an unactivated arene.