Highly Active Titanium-Based Olefin Polymerization Catalysts Bearing Bulky Aminopyridinato Ligands

Abstract

A series of titanium complexes have been prepared using either salt metathesis or amine elimination reactions. Reacting the potassium salt of Ap*H {Ap*H = N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine} (1) with [TiCl(4)(THF)(2)] results in the formation of a nucleophilic ring-opening product of the coordinated tetrahydrofuran (THF) ligand [Ap*TiCl(2)(OC(4)H(8)Cl)] (7). Alkylation with benzylmagnesium chloride gave rise to the corresponding benzyl complex [Ap*TiBn(2)(OC(4)H(8)Cl)] (8). However, THF ring opening was overcome by adopting an amine elimination route instead of salt metathesis. Mono(aminopyridinato)titanium trichloro complexes were prepared in high yields using [(CH(3))(2)NTiCl(3)], together with the corresponding sterically demanding aminopyridine as the starting material. The synthesized complexes could then be alkylated selectively. These complexes were characterized by spectroscopic methods, and their behavior in olefin polymerization and copolymerization of ethene and propene was explored. These mono(aminopyridinato)titanium trichloro complexes are less active if activated with methylaluminoxane (MAO). However, the activity increases strongly if MAO is replaced by d-MAO ("dry methylaluminoxane"). The catalysts show moderate activity toward propene polymerization, while ethylene-propylene copolymers in high-productivity with separated propene units were observed. The catalysts are also highly active in the co- and terpolymerization of 2-ethylidenenorbornene (ENB) with ethylene or ethylene-propylene, together with a very good incorporation of ENB. In all cases, the activity increases with an increase in the steric bulk of the protecting ligand.

Aminopyridine stabilized group-IV metal complexes and their applications

“…Kempe et al assumed that increasing the steric bulk of the aminopyridinato ligand could address these problems and synthesized Ti-complexes with bulky Ap ligands [37]. Such bulky Ap ligands could be synthesized in higher yields by Pd(0)-catalyzed coupling reactions of anilines with 2,6-dibromopyridines.…”

“…Such bulky Ap ligands could be synthesized in higher yields by Pd(0)-catalyzed coupling reactions of anilines with 2,6-dibromopyridines. Prior to complex formation reaction, the ligands are converted into their lithium/sodium/potassium salts by reacting the corresponding ligand with n-BuLi or with sodium and potassium hydride [37,55]. Equimolar reaction of potassium salt of aminopyridine [N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl-amine] and [TiCl 4 (THF) 2 ] gave the tetrahydrofuran ring-opening product 11 in 68 % yield (Scheme 7) [37].…”

“…Prior to complex formation reaction, the ligands are converted into their lithium/sodium/potassium salts by reacting the corresponding ligand with n-BuLi or with sodium and potassium hydride [37,55]. Equimolar reaction of potassium salt of aminopyridine [N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl-amine] and [TiCl 4 (THF) 2 ] gave the tetrahydrofuran ring-opening product 11 in 68 % yield (Scheme 7) [37]. Plausibly, free chloride is generated during reaction which attacks on the activated C-O bond of THF causing ring-opening reaction, and such a reaction for Ti was recently reported by Kempe et al, whereas previous reports were based upon zirconium, boron, uranium and yttrium complexes [48].…”

“…The coordinated THF with the metal center enhances its reactivity as well as solubility in organic solvents, and hence, use of TiCl 4 (THF) 2 is suggested for such reactions instead of TiCl 4 . The synthesis of complex 12 was achieved by treating two equivalents of benzylmagnesium chloride with 11 [37]. The yield of the complex 12 is only 47 %, and such a lower yield is attributed to the formation of side products.…”

“…13) and shorter amido-N-Hf bond than the pyridine-N-Hf bond indicating the location of negative charge on amido nitrogen atom [34]. Zr-complexes (33)(34)(35)(36)(37)(38) and Hf-complexes (43)(44)(45)(46)(47)(48) showed moderate activities for ethylene polymerization which has been presumed due to poor stability in the presence of aluminum alkyls [26,30,34]. Kempe et al hypothesized that diamine (containing an amine function at two and six position of pyridine ring)-functionalized ligands (electron rich-ligands) could enhance the stability of complex, and, hence, synthesized Hf-complexes containing electron-rich ligands through toluene elimination route [34].…”