Elsevier

Applied Catalysis A: General

Volume 525, 5 September 2016, Pages 137-144
Applied Catalysis A: General

Novel diamine-bis(phenolate) Ti(IV) complexes – tuning the complex structure to control catalytic properties in α-olefin polymerization

https://doi.org/10.1016/j.apcata.2016.07.019Get rights and content

Highlights

  • Titanium complexes of amine bis(phenolate) ligands having an extra donor arm were synthesized by reaction of deprotonated ligands with TiCl4.

  • Relationships between complex structure, cocatalyst type and product properties was investigated.

  • Complexes produced poli(α-olefin) with different microstructure (from isotactic to pure atactic) and different molecular weight.

Abstract

Four monomeric titanium(IV) dichloride complexes of amine-bis(phenolate) ligands having an extra donor arm (2a–2d) and one oxo-bridged complex 3 were successfully synthesized in the reaction of TiCl4 with a sodium salt of the appropriate ligand, and they were characterized by 1H NMR spectroscopy. The ligands had either a dimethylamino side‐arm donor and t-Bu substituents on both (1a) and one (1d) phenolate rings or a diisopropylamino side-arm donor and t-Bu (1b) and t-Bu along with OMe (1c) phenolate substituents. All complexes upon activation with [Ph3CB(C6F5)4] and MAO were used to catalyze polymerization of 1-octene (in liquid monomer) into poly(1-octene). Their activities as well as product microstructures were found to be highly dependent on the structure of the diamine-bis(phenolate) ligand. The catalytic activities of the complexes towards 1-olefin polymerization decreased in the following order: 2a >> 2b > 2c > 2d. The polymers produced were atactic or isotactic with the [mmmm] pentad content varied from about 4 up to 90%. The highest isotacticity was exhibited by poly(1-octene) synthesized by 2d. The catalytic activities increased and polymer molecular weight decreased with the increasing reaction temperature. Moreover, catalyst 2a/Al(iBu)3Ph3CB(C6F5)4 was used in the bulk polymerization of other α-olefin and it was found that the monomer conversion decrease in the order: 1-octene > 1-decene > 1-dodecene > 1-hexene >> 4-methyl-1-pentene.

Introduction

Polymerization of α-olefins by homogeneous catalysts which contain group 4 Cp-free metal complexes has attracted considerable interest in recent years due to the ability to produce polymers with narrow molecular weight distributions, controllable molecular weights, and required atactic or stereoregular microstructures [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Many complexes of that type have been prepared and two classes seem to be particularly attractive among them: with tetradentate diamine-bis(phenolate) ligands introduced by Kol and coworkers, e.g. complexes with ligands having the donors connected in the sequential mode (salan ligands), and in the “branched” mode (featuring sidearm donors), which turned out to be versatile precatalyst for α-olefin polymerization [6], [13]. For example, dibenzyl titanium complexes of salan ligands produce, at high yields, ultrahigh molecular weight poly(1-hexene) of different isotacticities controlled by the size of phenolate substituents, whereas zirconium complexes of that type give low Mw atactic products [4]. Moreover, C1-symmetric zirconium complexes that include differently substituted phenolate rings can give steroregular polymers [14].

The chemical reactivity of the catalysts derived from diamine-bis(phenolate) titanium dibenzyl complexes with the dimethylamino donor group on a sidearm showed a strong dependence on both steric and electronic properties of phenolate substituents. The complex that carried chloro groups showed one of the highest activity reported for 1-hexene polymerization and it led to the atactic product with the molecular weight which was unusually high (a few million) [15]. The titanium complexes having t-Bu substituents catalyzed the living polymerization of α-olefins at room temperature [16]. The activities of the zirconium complexes and the molecular properties of the resulting polymers could also be controlled by adjusting the ligand structure [1]. Until recently, however, microstructures of poly(α-olefins) could not be controlled in practice in the presence of the catalysts which bear amine-bis(phenolate) ligands with a sidearm donor. A somewhat improved control of tacticity was achieved with bimetallic zirconium complexes for the synthesis in which binucleating multidentate ligands were utilized. At ambient temperatures, these complexes gave polymers with [mmmm] up to 41% and only poly(1-hexene) synthesized at −30 °C reached the isotacticity value as high as 79% [17]. And the only example of highly stereoregular poly(α‐olefin) synthesized at high temperature (up to 87% [mmmm] at 70 °C) was that obtained with the dimeric zirconium complex which was bearing the new unsymmetrically substituted ligand synthesized by us [18]. Taking into account that the control of tacticity in the synthesis of poly(α-olefins) can be achieved by fine tuning of the ligand structure and by the choice of the transition metal, we decided to synthesize the titanium complexes of various structures, and namely the complexes that include NMe2 or N(i-Pr)2 donor groups and diversely substituted aromatic rings. These complexes were prepared for the first time in the direct reaction of the deprotonated diamine-bis(phenolate) ligands with TiCl4. Moreover, we presented in this report the effects that the changes in the complex structures, in the cocatalyst type and in polymerization conditions had on the catalyst activity, on the molecular weight and on microstructures of the resulting polymers.

Section snippets

Experimental

All air- and/or moisture sensitive compounds were handled under an inert atmosphere of argon or nitrogen, using the standard Schlenk line techniques and a glove box.

Synthesis of complexes

In contrast to titanium(IV) dibenzyl complexes [4], [15], [16], [22], examples of titanium(IV) dichloro complexes supported by amine-bis(phenolate) ligands having an extra donor arm are very rare up to now. Only Barroso et al. reported the synthesis of monomeric [Ti(tBuO2NN′)Cl2] and dimeric [Ti(tBuO2NN′)Cl]2(μ-O)]2 complexes of that type. Their synthesis, however, involved a procedure with a few steps and the final products were obtained in the reaction of [Ti(tBuO2NN′)Cl(S)] (S = THF, py) with

Conclusions

Diamine-bis(phenolate) titanium(IV) dichloro complexes were synthesized for the first time in the direct reaction of deprotonated ligand with titanium tetrachloride. Apart from monomeric complexes (2a2d), the oxo-bridged one (3) was obtained by slight modification of the synthesis procedure. These complexes in conjunction with borate or MAO activators turned out to be active in the polymerization process of 1-octene. Their catalytic properties were found to be highly dependent on the ligand

Justification for publication

The results presented in the manuscript explain how the structure of amine-bis(phenolate) ligand with sidearm donor affect the microstructure of synthesised poly(1-olefin). We were able to obtain the polymers with [mmmm] varied from about 4–90% (it is the most stereoregular PO synthesised with such type of catalyst). Moreover, the investigated dichloro titanium complexes were the first time obtained by reaction of sodium salt of ligand with transition metal tetrachloride. Before, synthesis of

Acknowledgements

This work was supported by the research grant (grant No. N N209 140840) from the National Science Center (NCN, Poland). W. Bukowski and G. Spaleniak are thanked for ligand synthesis.

References (31)

  • L.A. Rishina et al.

    Polymer

    (2013)
  • E.Y. Tshuva et al.

    Inorg. Chem. Commun.

    (1999)
  • E.Y. Tshuva et al.

    Inorg. Chem. Commun.

    (2000)
  • E. Bisz et al.

    Appl. Catal. A: Gen.

    (2015)
  • G. Dutta et al.

    Polyhedron

    (2011)
  • E.Y. Tshuva et al.

    Organometallics

    (2001)
  • V.C. Gibson et al.

    Chem. Rev.

    (2003)
  • H. Makio et al.

    Adv. Synth. Catal.

    (2002)
  • S. Segal et al.

    Organometallics

    (2005)
  • N. Nakata et al.

    Macromolecules

    (2013)
  • E.Y. Tshuva et al.

    J. Am. Chem. Soc.

    (2000)
  • N. Nakata et al.

    Inorg. Chem.

    (2012)
  • J.D. Scollard et al.

    Macromolecules

    (1996)
  • J. Saito et al.

    Macromolecules

    (2006)
  • K. Press et al.

    Angew. Chem. Int. Ed.

    (2011)
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