Novel diamine-bis(phenolate) Ti(IV) complexes – tuning the complex structure to control catalytic properties in α-olefin polymerization
Graphical abstract
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 (2a–2d), 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)
- et al.
Polymer
(2013) - et al.
Inorg. Chem. Commun.
(1999) - et al.
Inorg. Chem. Commun.
(2000) - et al.
Appl. Catal. A: Gen.
(2015) - et al.
Polyhedron
(2011) - et al.
Organometallics
(2001) - et al.
Chem. Rev.
(2003) - et al.
Adv. Synth. Catal.
(2002) - et al.
Organometallics
(2005) - et al.
Macromolecules
(2013)
J. Am. Chem. Soc.
Inorg. Chem.
Macromolecules
Macromolecules
Angew. Chem. Int. Ed.
Cited by (7)
Synthesis, characterization, NMR spectroscopic, and X-ray crystallographic studies of new titanium(IV) Schiff base salen complexes: Formation of intriguing titanium(IV) species
2020, Inorganica Chimica ActaCitation Excerpt :We have utilized various substituent groups to tune the reactivity and the stability of the complexes. To the best of our knowledge, there have been very few reports of oxo-bridged binuclear titanium Schiff base complexes in the literature [15,21,23,28–35]. Herein, we have also carried out 49Ti NMR spectroscopic studies in deuterated chloroform, which is also new for such complexes.
Dichlorovanadium(IV) diamine-bis(phenolate) complexes for ethylene (co)polymerization and 1-olefin isospecific polymerization
2018, Journal of CatalysisCitation Excerpt :1H NMR (400 MHz, C6D6, δ): 9.93 (br, 2H, HOAr), 7.48 (d, 1H, ArH), 6.95 (d, 1H, ArH), 7.19–6.76 (ArH), 3.40 (s, 2H, NCH2Ar), 3.23 (s, 2H, NCH2Ar), 2.14 (t, 2H, CH2), 1.92 (t, 2H, CH2), 1.92 (s, 6H, N(CH3)2), 1.60 (s, 9H, C(CH3)3), 1.36 (s, 9H, C(CH3)3). Complexes 1 and 2 were synthesized according to literature procedure reported for titanium and zirconium complexes bearing the same diamino-bis(phenolate) ligands [19,20]. A solution of Lig1H2 (1.980 g, 3.77 mmol) in tetrahydrofuran was added dropwise to a suspension of NaH (0.302 g, 7.54 mmol) in THF at room temperature.
Homopolymerization of styrenic monomers and their copolymerization with ethylene using group 4 non-metallocene catalysts
2020, Journal of Applied Polymer Science