Sterically Less‐Hindered Half‐Titanocene(IV) Phenoxides: Ancillary‐Ligand Effect on Mono‐, Bis‐, and Tris(2‐Alkyl‐/arylphenoxy) Titanium(IV) Chloride Complexes |
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| Authors: | Tae‐Jin Kim Sung‐Kwan Kim Beom‐Jun Kim Ho‐Jin Son Jong Sok Hahn Minserk Cheong Prof Mariusz Mitoraj Dr Monika Srebro Łukasz Piękoś Artur Michalak Prof Sang Ook Kang Prof |
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| Institution: | 1. Department of Advanced Materials Chemistry, Sejong, Korea University, 208 Seochang, Chochiwon, Chung‐nam 339‐700 (Korea), Fax: (+82)?41‐867‐5396;2. Polymer Lab, Institute of Technology, SK Energy, 140‐1 Wonchon‐dong, Yusung‐gu, Daejeon, 305‐712 (Korea);3. Department of Chemistry and Research Institute for Basic Sciences, Kyung Hee University, Hoegi‐dong, Dondaemun‐gu, Seoul, 139‐701 (Korea);4. Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30‐060 Cracow (Poland), Fax: (+48)?12‐634‐0515 |
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| Abstract: | A series of mono‐, bis‐, and tris(phenoxy)–titanium(IV) chlorides of the type Cp*Ti(2‐R? PhO)nCl3?n] (n=1–3; Cp*=pentamethylcyclopentadienyl) was prepared, in which R=Me, iPr, tBu, and Ph. The formation of each mono‐, bis‐, and tris(2‐alkyl‐/arylphenoxy) series was authenticated by structural studies on representative examples of the phenyl series including Cp*Ti(2‐Ph? PhO)Cl2] ( 1 PhCl2 ), Cp*Ti(2‐Ph? PhO)2Cl] ( 2 PhCl ), and Cp*Ti(2‐Ph? PhO)3] ( 3 Ph ). The metal‐coordination geometry of each compound is best described as pseudotetrahedral with the Cp* ring and the 2‐Ph? PhO and chloride ligands occupying three leg positions in a piano‐stool geometry. The mean Ti? O distances, observed with an increasing number of 2‐Ph? PhO groups, are 1.784(3), 1.802(4), and 1.799(3) Å for 1 PhCl2 , 2 PhCl , and 3 Ph , respectively. All four alkyl/aryl series with Me, iPr, tBu, and Ph substituents were tested for ethylene homopolymerization after activation with Ph3C+B(C6F5)4]? and modified methyaluminoxane (7% aluminum in isopar E; mMAO‐7) at 140 °C. The phenyl series showed much higher catalytic activity, which ranged from 43.2 and 65.4 kg (mmol of Ti?h)?1, than the Me, iPr, and tBu series (19.2 and 36.6 kg (mmol of Ti?h)?1). Among the phenyl series, the bis(phenoxide) complex of 2 PhCl showed the highest activity of 65.4 kg (mmol of Ti?h)?1. Therefore, the catalyst precursors of the phenyl series were examined by treating them with a variety of alkylating reagents, such as trimethylaluminum (TMA), triisobutylaluminum (TIBA), and methylaluminoxane (MAO). In all cases, 2 PhCl produced the most catalytically active alkylated species, Cp*Ti(2‐Ph? PhO)MeCl]. This enhancement was further supported by DFT calculations based on the simplified model with TMA. |
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| Keywords: | alkylation density functional calculations polymerization titanium |
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