Titanium and Zirconium Complexes That Contain the Tridentate Diamido Ligands [(i-PrN-o-C₆H₄)₂O]^2-([i-PrNON]^2-) and [(C₆H₁₁N-o-C₆H₄)₂O]^2-([CyNON]^2-)

Abstract

A variety of five- and six-coordinate titanium and zirconium dialkyl complexes that contain the [(i-PrN-o-C6H4)2O]2- ([i-PrNON]2-) ligand have been prepared, among them [i-PrNON]Ti(CH2CHMe2)2, [i-PrNON]Ti(CH2CMe3)2, [i-PrNON]Zr(CH2CH3)2, and [i-PrNON]Zr(CH2CHMe2)2. These species serve as sources of complexes such as {[i-PrNON]Ti(PMe3)2}2(μ-N2), [i-PrNON]Ti(CHCMe3)(PMe3)2, [i-PrNON]Zr(CH2CHMe2)2(PMe3), and [i-PrNON]Zr(H2CCMe2)(PMe3)2. The reaction between [i-PrNON]Ti(CH2CMe3)2 and Me2PCH2CH2PMe2 in the absence of dinitrogen yields (i-PrNC6H4)(i-PrNC6H4O)Ti(dmpe), a pseudooctahedral species in which one aryl−oxygen bond has been cleaved. In all structurally characterized complexes in which the [i-PrNON]2- ligand is intact, it adopts a mer configuration in which the donor oxygen atom is planar. Analogous dialkyl complexes [CyNON]MR2 (Cy = cyclohexyl; M = Zr, R = Me, Et, i-Bu, CH2CMe3, allyl; M = Ti, R = Me, CH2CMe3, i-Bu) have also been prepared. Decomposition of [i-PrNON]Zr(CH2CH3)2 in the absence of phosphine has been found to proceed in a first-order manner to yield {[i-PrNON]Zr(CH2CH3)}2(μ-C2H4) via rate-limiting β-hydrogen abstraction to give transient [i-PrNON]Zr(CH2CH2) followed by either intermolecular selective β-hydrogen transfer or ethyl group transfer from [i-PrNON]Zr(CH2CH3)2 to [i-PrNON]Zr(CH2CH2), as suggested by 2H and 13C labeling studies. Decompositions of [i-PrNON]ZrR2 complexes are dramatically accelerated in the presence of PMe3. One equivalent of PMe3 is proposed to bind to give a pseudooctahedral adduct, [i-PrNON]ZrR2(PMe3), in which the two alkyl (R) groups are pushed close to one another and β-hydrogen abstraction is thereby accelerated. Consistent with the relatively uncrowded coordination sphere in [i-PrNON]2- or [CyNON]2- complexes, activated dialkyls will only oligomerize 1-hexene. Compounds whose structures have been determined include [i-PrNON]Ti(CH2CHMe2)2, [i-PrNON]ZrMe2, [i-PrNON]Zr(H2CCHMe2)2(PMe3), [i-PrNON]Zr(CH2CMe2)(PMe3)2, [i-PrNON]Ti(PMe3)2]2(μ-N2), [i-PrNON]Ti(CHCMe3)(PMe3)2, and (i-PrNC6H4)(i-PrNC6H4O)Ti(dmpe).