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

Abstract

A variety of five- and six-coordinate titanium and zirconium dialkyl complexes that contain the [( i -PrN- o -C 6 H 4 ) 2 O] 2 - ([ i -PrNON] 2 - ) ligand have been prepared, among them [ i -PrNON]Ti(CH 2 CHMe 2 ) 2, [ i -PrNON]Ti(CH 2 CMe 3 ) 2, [ i -PrNON]Zr(CH 2 CH 3 ) 2, and [ i -PrNON]Zr(CH 2 CHMe 2 ) 2 . These species serve as sources of complexes such as {[ i -PrNON]Ti(PMe 3 ) 2 } 2 (μ-N 2 ), [ i -PrNON]Ti(CHCMe 3 )(PMe 3 ) 2, [ i -PrNON]Zr(CH 2 CHMe 2 ) 2 (PMe 3 ), and [ i -PrNON]Zr(H 2 C CMe 2 )(PMe 3 ) 2 . The reaction between [ i -PrNON]Ti(CH 2 CMe 3 ) 2 and Me 2 PCH 2 CH 2 PMe 2 in the absence of dinitrogen yields ( i -PrNC 6 H 4 )( i -PrNC 6 H 4 O)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]MR 2 (Cy = cyclohexyl; M = Zr, R = Me, Et, i -Bu, CH 2 CMe 3, allyl; M = Ti, R = Me, CH 2 CMe 3, i-Bu) have also been prepared. Decomposition of [ i -PrNON]Zr(CH 2 CH 3 ) 2 in the absence of phosphine has been found to proceed in a first-order manner to yield {[ i -PrNON]Zr(CH 2 CH 3 )} 2 (μ-C 2 H 4 ) via rate-limiting β-hydrogen abstraction to give transient [ i -PrNON]Zr(CH 2 CH 2 ) followed by either intermolecular selective β-hydrogen transfer or ethyl group transfer from [ i -PrNON]Zr(CH 2 CH 3 ) 2 to [ i -PrNON]Zr(CH 2 CH 2 ), as suggested by 2 H and 13 C labeling studies. Decompositions of [ i -PrNON]ZrR 2 complexes are dramatically accelerated in the presence of PMe 3 . One equivalent of PMe 3 is proposed to bind to give a pseudooctahedral adduct, [ i -PrNON]ZrR 2 (PMe 3 ), 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(CH 2 CHMe 2 ) 2, [ i -PrNON]ZrMe 2, [ i -PrNON]Zr(H 2 C CHMe 2 ) 2 (PMe 3 ), [ i -PrNON]Zr(CH 2 CMe 2 )(PMe 3 ) 2, [ i -PrNON]Ti(PMe 3 ) 2 ] 2 (μ-N 2 ), [ i -PrNON]Ti(CHCMe 3 )(PMe 3 ) 2, and ( i -PrNC 6 H 4 )( i -PrNC 6 H 4 O)Ti(dmpe).