Oscillating Non‐Metallocenes – from Stereoblock‐Isotactic Polypropylene to Isotactic Polypropylene via Zirconium and Hafnium Dithiodiphenolate Catalysts

Abstract

Octahedral group 4 complexes of a new bulky tetradentate dithiodiphenolate {OSSO}‐type ligand that oscillate between two enantiomeric C2‐symmetric conformations are described. The dibenzyl Zr and Hf complexes led to active catalysts in propylene polymerization. Polypropylene having predominantly stereoblock‐isotactic microstructure or predominantly isotactic microstructure could be obtained by varying the polymerization conditions. Long isotactic blocks of 50 to more than 100 repeat units were formed at –10 °C in liquid propylene.

Highly Active and Isospecific Styrene Polymerization Catalyzed by Zirconium Complexes Bearing Aryl-substituted [OSSO]-Type Bis(phenolate) Ligands

“…The molecular structure of diphenyl derivative 9 was confirmed by X-ray crystallography, as shown in Figure 1. In the crystalline state, the zirconium center possesses a distorted octahedral geometry with cis -arranged two sulfur atoms and two benzyl groups, adopting a cis -α configuration as similar as the previously reported [OSSO]-type zirconium(IV) complexes [49,50,57,58,59,60]. One benzyl ligand of 9 is coordinated to the zirconium center by η 1 -mode with the Zr–C benzyl –C ipso angle of 124.3(2)°, whereas the other has an acute Zr–C benzyl –C ipso angle of 84.4(2)° consistent with the η 2 -coordination fashion as similarly as in the case of t Bu-substituted complex 5a ; the Zr-C ipso distance (2.592(3) Å) is extremely shortened compared with that in 5a (2.820(3) Å) [48], indicating that this η 2 -benzyl group in 9 is strongly bound to the metal than that in 5a due to the less steric hindrance around the zirconium center in 9 as expected.…”

Stereorigid OSSO-Type Group 4 Metal Complexes in the Ring-Opening Polymerization of rac-Lactide

“…Interestingly, not only the two phenolate groups in trans positions are pulled away from the tert-butoxy ligands (O1−Zr−O2 152.56(4)°) but also two terminal cumyl groups of the OSSO ligand point toward the inner thiocathecolate ring from opposite directions. The Zr−S distances (Zr−S1 2.8703(4) Å and Zr−S2 2.8797(4) Å) are significantly longer than those found in the other two similar [(OSSO)Zr(O-tBu) 2 ] complexes (Zr−S 2.828(1) and 2.8279 (7) and 2.8485(7) Å), 13,14 presumably in order to alleviate a worse steric congestion around the Zr atom. The Zr−O(alkoxy) and Zr−O(OSSO) distances fall in the range normally found for these kinds of complexes.…”

“…As expected for [OSSO]-and [ONNO]-type complexes, 14 the Zr atom possesses an octahedral environment in which the [OSSO] ligand adopts a fac-fac wrapping coordination mode with the tert-butyloxy ligands in mutually cis positions. The metal atom is involved in a perfectly planar disulfometallacyclopentane ring with an S1−Zr−S2 bite angle of 70.93(2)°, whereas in the two previously reported structures of [OSSO]-Zr-OtBu complexes 13,14 the Zr atom forms with the [OSSO] ligand puckered five-membered rings with wider S1−Zr−S2 bite angles of 73.80(2) and 73.84(5)°. Interestingly, not only the two phenolate groups in trans positions are pulled away from the tert-butoxy ligands (O1−Zr−O2 152.56(4)°) but also two terminal cumyl groups of the OSSO ligand point toward the inner thiocathecolate ring from opposite directions.…”

“…1 H NMR spectra are referenced using the residual solvent peak at δ 7.16 for C 6 D 6 , δ 7.27 for CDCl 3 , and δ 5.32 for CD 2 Cl 2 . 13 C NMR spectra are referenced using the residual solvent peak at δ 128.39 for C 6 D 6 , δ 77.23 for CDCl 3 , and δ 53.84 for CD 2 Cl 2 . Variable-temperature 1 H NMR experiments were recorded with a Bruker ASCEND 600 spectrometer in toluene-d 8 using a J.…”

“…Similar tetradentate [OSSO] zirconium complexes with an ethylene bridge and a 6-5-6 array of chelate rings are rigid at room temperature but become fluxional upon warming at 100 °C, with a coalescence temperature of 85 °C. 13 The existence of fluxional behavior in the slow-exchange regime for 1 was investigated by 1 H− 1 H EXSY experiments at 60 °C. As shown in Figure 2, positive cross-peaks correlating the signals of methylene groups were clearly detected.…”