Anisole−Diphenoxide Ligands and Their Zirconium Dichloride and Dialkyl Complexes

Linear triphenol H₃[^RO₃] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-phenol; R = Me, ^tBu) was found to undergo selective mono-deprotonation and mono-O-methylation. Deprotonation of H₃[^RO₃] with 1 equiv of ⁿBuLi resulted in the formation of Li{H₂[^RO₃]}(Et₂O)₂ (R = Me (1a), ^tBu (1b)), in which the central phenol unit was lithiated. Treatment of H₃[^RO₃] with methyl p-toluenesulfonate in the presence of K₂CO₃ in CH₃CN gave the corresponding anisol-diphenol H₂[^RO₂O] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-anisole; R = Me (2a), ^tBu (2b)). Reaction of H₂[^RO₂O] with 2 equiv of ⁿBuLi gave the dilithiated derivatives Li₂[^RO₂O]. The lithium salts were reacted with ZrCl₄ in toluene/THF to obtain the dichloride complex [^RO₂O]ZrCl₂(thf) (R = Me (3a), ^tBu (3b)). 3b underwent dimerization along with a loss of THF to generate {[^tBuO₂O]ZrCl₂}₂ (4), whereas 4 was dissolved in THF to regenerate the monomer 3b. Alkylation of 3 with MeMgBr, PhCH₂MgCl, and Me₃SiCH₂MgCl gave [^MeO₂O]ZrMe₂(thf) (5), [^RO₂O]Zr(CH₂Ph)₂ (R = Me (6a), ^tBu (6b)), and [^tBuO₂O]Zr(CH₂SiMe₃)₂ (7), respectively. Reaction of 3b with LiBHEt₃ produced the hydride-bridged dimer [Li₂(thf)₄Cl]{[^tBuO₃]Zr}₂(μ−H)₃} (8), in which demethylation of the dianionic [^tBuO₂O] ligand took place to give the trianionic [^tBuO₃] ligand. The X-ray crystal structures of 1b, 2a, 3a, 4, 6a, and 7 were reported.