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 ({LON^R}­H₂, R = iPr, 2,6-iPr₂C₆H₃ (Ar)) and new guanidine-phenol {4,6-tBu₂C₆H₂ON­(C₆H₅)­(2-C­(NR)NR}­H₂ ({LON­(Ph)­N^iPr}­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 {LON^R}­H₂ and Zr­(CH₂Ph)₄ afforded mixed-ligand monobenzyl {LO^HN^R}­{LON^R}­Zr­(CH₂Ph) (R = iPr; 1) and monoligand tribenzyl {LO^HN^Ar}­Zr­(CH₂Ph)₃ (R = Ar; 2) complexes, respectively. Alkane and amine elimination reactions between {LON­(Ph)­N^iPr}­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 {LON^R}­Li₂ and ZrCl₄(THF)_n (n = 0, 2), conducted in 1:1 ratios, led upon crystallization to diverse chloro complexes: [{LON^iPr}­ZrCl]₃(μ₃-O)­(μ₃-Cl) (5), [{LON^Ar}₂ZrCl­(μ₂-Cl)]₂[{L^HON^Ar}­ZrCl­(μ₂-Cl)]­(μ₃–OH) (6), and {LO^HN^Ar}­ZrCl₃(THF) (7). Similar salt metathesis reactions between the monolithium salts {L^HON^R}Li and ZrCl₄, conducted in 2:1 ratios, allowed the selective preparation of bis­(phenoxy-amidine) complexes with pendant amino groups {LO^HN^R}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.