Zirconium and hafnium complexes of the thio(bisphenolato) ligand: synthesis, structural characterization and testing as 1-hexene polymerization catalysts

Abstract

Thio(bisphenolato) complexes of the type [M2(mu-tbop-kappa3O,S,O)2Cl4] [M = Zr 1, Hf 2 and tbop = 2,2-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenolate}] were prepared by HCl elimination from tbopH2 and MCl4. Substitution of the chlorides in 1 and 2 by 2,6-diisopropylphenolato groups (dipp) generates new compounds [M2(mu-tbop-kappa3O,S,O)2(dipp)4] (M = Zr 3, Hf 4). The structures of 1-4 were confirmed by NMR spectroscopy; complexes 3 and 4 were further investigated by X-ray crystallography. These studies showed 1-4 to be dimers either in the solid state or in solution and to have metal centers adopting distorted octahedral geometry. However treatment of MCl4 with [Al2(mu-OEt)2(tbop-kappa3O,S,O)2] or [Al2(mu-tbop-kappa3O,S,O)2Me2] gave heterotrinuclear complexes [M(tbop-kappa3O,S,O)2Cl2(mu-AlX2)2] (M = Zr, X = Cl 5, X = Me 7 and M = Hf, X = Cl 6, X = Me 8) for which the single-crystal X-ray diffraction analysis showed zirconium and hafnium centers to have eight-coordinate dodecahedral geometry. Complexes 1-6 after activation with aluminium alkyls and supporting on MgCl2 showed a lack of activity in the ethene polymerization process and moderate activity towards 1-hexene producing high molecular weight atactic poly(1-hexenes).

A Tetranuclear Planar Hafnium Complex Containing O–Hf–S Moieties

“…[24] Nevertheless, in addition to the signals assigned to butyl acetate, the 1 H and 13 C spectra consist of broad resonances typical for the n-butoxy moieties (see Experimental Section), which may arise from the butoxy groups that are bonded to the Hf core and are involved in relatively slow chemical exchange processes. Moreover, some weaker and very broad 1 H signals appear in the range δ = 2.4-2.6 ppm, which exhibit (i) a set of onebond H-C heteronuclear correlations with a number of broad 13 C resonances centred at δ = 35.9 ppm and (ii) two sets of multiple-bond correlations with very broad 13 C signals around δ = 240 and δ = 260 ppm. These signals may be assigned to the 13 C nuclei of methyl and thiocarbonyl subunits, respectively, of the thioacetate groups in different coordinative situations around the metal core undergoing a slow chemical exchange.…”

“…Moreover, some weaker and very broad 1 H signals appear in the range δ = 2.4-2.6 ppm, which exhibit (i) a set of onebond H-C heteronuclear correlations with a number of broad 13 C resonances centred at δ = 35.9 ppm and (ii) two sets of multiple-bond correlations with very broad 13 C signals around δ = 240 and δ = 260 ppm. These signals may be assigned to the 13 C nuclei of methyl and thiocarbonyl subunits, respectively, of the thioacetate groups in different coordinative situations around the metal core undergoing a slow chemical exchange. Very similar and unprecedented chemical shift values for the thiocarbonyl subunits have been observed in comparable Zr-oxothioclusters [23] and are attributed to the thiocarbonyl moieties by using the principal component analysis (PCA) [25] as developed by Rittner et al [26] …”

Recent advancements in N-ligated group 4 molecular catalysts for the (co)polymerization of ethylene

“…More importantly, 62 exhibited excellent thermal stability at an industrially relevant 80 ºC. By comparison, the hafnium catalyst 64 generally showed lower polymerization activity [162][163][164][165][166][167][168][169][170][171][172] than the corresponding titanium and zirconium counterparts. This finding was attributed to either an increased barrier to monomer insertion with hafnium [173] or to less efficient activation by MAO [174,175].…”