C O M M U N I C A T I O N S
substituents on the phenolate rings).2,7 No significant effects of the
4,5-dichlorophenylene bridge substituents on activity or polymer
characteristics were observed, and the polymers obtained were
atactic. Lig1ZrBn2 and Lig3ZrBn2 that feature tert-butyl phenolate
groups were less actives1.0 and 5.6 g mmol-1 h-1, respectively.
Namely, withdrawing electron density from the N-donors causes a
significant increase in reactivity in this case. The 13C NMR spectra
indicated that these two polymers were mildly isotactic (mmmm
of ca. 65%) and supported an enantiomorphic-site control mech-
anism (see the Supporting Information). In comparison, the iso-
tacticity of the poly(1-hexene) derived from the corresponding
zirconium Salan complex was much higher.1 It is not clear, at this
stage, whether the lower stereocontrol results from the Salophan
backbone rigidity or from the slight geometrical differences between
the Salan and Salophan wrapping around the zirconium.
In conclusion, we have introduced the first Salophan ligands that
retain their dianionic character in different environments and are
amenable to fine-tuning of the electronic character of the N-donors.
These ligands have led to promising catalysts for polymerization
of R-olefins.
Figure 1. Crystal structure of Lig1Zr(O-tert-Bu)2 (left) and its analogous
Salan complex (right). For clarity, only the O atoms of the tert-Bu-O labile
groups are shown.
crystal structure is shown in Figure 1 next to the structure of the
analogous Salan complex that was previously published.12
Acknowledgment. We thank Ad Cohen for help with the
ligands synthesis. We thank the Israel Science Foundation and the
Ministry of Science for financial support.
The structure reveals an octahedral complex in which the
Salophan ligand wraps around the zirconium in the desired fac-
fac mode typical of the Salan ligands. The zirconium atom lies
within the N-C-C-N bridge forming a practically planar diaza-
metallacyclopentane (0.034 Å deviation from plane), unlike the
puckered Salan complex. The Salophan and Salan complexes share
similar N-Zr-N bite angles of 69.2 and 71.4°, respectively,
identical O-Zr-O angle between the labile groups (107.7°) and
Zr-O bond lengths (1.93 Å), and similar Zr-O-C bond angles
(ca. 165°), indicating that the labile groups in the two complexes
reside in similar environments. Yet, the Salophan complex appears
more compact, with the phenolate groups pulled back from the labile
groups and bent toward the aromatic bridge. The diminished
protrusion of the ortho-tert-Bu groups might impair their stereo-
regulating induction. The crystal structure of the complex Lig3Zr-
(O-tert-Bu)2 was solved, as well (see the Supporting Information),
and featured practically identical bond lengths and angles around
the zirconium. Namely, the electron deficiency of this ligand is
not apparent in its bonding parameters to the metal.
Supporting Information Available: Details of the synthesis and
characterization of the ligands and complexes, crystallographic data in
text format for Lig1Zr(O-tert-Bu)2 and Lig3Zr(O-tert-Bu)2, polymeri-
zation procedures, and polymer characterization. This material is
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To explore the activity of the new Salophan systems in
polymerization, we attempted the synthesis of dibenzylzirconium
complexes by reacting the ligand precursors with ZrBn4. All
reactions gave undefined products at room temperature that
converted to C2-symmetric dibenzyl complexes upon heating to
75 °C, according to their 1H NMR spectra. These are the first alkyl
complexes of dianionic Salophan ligands reported with any metal.
Upon activation with B(C6F5)3, all four dibenzylzirconium
complexes led to active 1-hexene polymerization catalysts. Lig2-
ZrBn2 and Lig4ZrBn2, the two complexes that include chloro
substituents on the phenolate rings, led to ultrahigh activities of
ca. 20 000 g mmol-1 h-1, which are considerably higher than those
exhibited by the most active Salan complexes (also featuring chloro
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2006, 45, 3478.
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(8) For biological activity of titanium Salan complexes, see: Shavit, M.; Peri,
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(11) The kinetic isomer appeared as C2- or Cs-symmetric by 1H NMR.
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