Synthesis and Structural Diversity of Group 4 Metal Complexes with Multidentate Tethered Phenoxy-Amidine and Phenoxy-Amidinate Ligands

The coordination chemistry of the multidentate tethered
amidine-phenol
{4,6-tBu2C6H2O­(2-C­(NR)NR}­H2 ({LONR}­H2, R = iPr,
2,6-iPr2C6H3 (Ar))
and new guanidine-phenol {4,6-tBu2C6H2ON­(C6H5)­(2-C­(NR)NR}­H2 ({LON­(Ph)­NiPr}­H2)
pro-ligands with group 4 metals has been studied. σ-Bond and
salt metathesis reactions were explored to coordinate these (pro)­ligands
onto zirconium and hafnium. Alkane elimination reactions between {LONR}­H2 and Zr­(CH2Ph)4 afforded
mixed-ligand monobenzyl {LOHNR}­{LONR}­Zr­(CH2Ph) (R = iPr; 1)
and monoligand tribenzyl {LOHNAr}­Zr­(CH2Ph)3 (R = Ar; 2) complexes, respectively.
Alkane and amine elimination reactions between {LON­(Ph)­NiPr}­H2 and Zr­(CH2Ph)4 or Hf­(NMe2)4 unexpectedly resulted in cleavage
of the ligand backbone and eventual isolation of {(Ph)­NC6H2(tBu)2O}­Zr­{(iPrN)2CCH2Ph}2 (3) and
{(Ph)­NC6H2(tBu)2O}­Hf­{(iPrN)2CNMe2}2 (4), respectively. Salt metathesis reactions between
{LONR}­Li2 and ZrCl4(THF)n (n = 0, 2), conducted in 1:1 ratios,
led upon crystallization to diverse chloro complexes: [{LONiPr}­ZrCl]3(μ3-O)­(μ3-Cl) (5), [{LONAr}2ZrCl­(μ2-Cl)]2[{LHONAr}­ZrCl­(μ2-Cl)]­(μ3–OH) (6), and
{LOHNAr}­ZrCl3(THF) (7). Similar salt metathesis reactions between the monolithium salts
{LHONR}Li and ZrCl4, conducted in
2:1 ratios, allowed the selective preparation of bis­(phenoxy-amidine)
complexes with pendant amino groups {LOHNR}2ZrCl2 (R = iPr, 8; R = Ar, 9). All complexes were authenticated by elemental
analysis, X-ray crystallography, and NMR spectroscopy. Complexes 5, 6, 8, and 9, upon
activation with MAO, showed poor to moderate productivities (4–172
(kg of PE) mol–1 h–1) in the polymerization
of ethylene, giving linear polymers with large polydispersities.