Studies of the Nature of the Catalytic Species in the α‐Olefin Polymerisation Processes Generated by the Reaction of Diamido(cyclopentadienyl)titanium Complexes with Aluminium Reagents as Cocatalysts

Abstract

The reaction of the diamido(chloro)cyclopentadienyltitanium compounds TiCpRx[1,2‐C6H4(NR′)2]Cl [CpRx = η5‐C5H5, η5‐C5(CH3)5, η5‐C5H4(SiMe3); R′ = CH2tBu, Pr] with the Grignard reagent MgClR (R = Me, CH2Ph) affords the monomethyl and monobenzyl derivatives TiCpRx[1,2‐C6H4(NR′)2]R. Upon addition of methylaluminoxane (MAO), the chloro‐ and alkyltitanium complexes show low activity towards the polymerisation of ethylene and styrene. However, no methylation was observed during the treatment of trimethylaluminium with the chloro compounds TiCpRx[1,2‐C6H4(NR′)2]Cl. Instead, these reactions give the dinuclear aluminium complexes Al2[1,2‐C6H4(NR′)2]Me4 (R′ = CH2tBu, Pr) through transmetallation of the diamido ligand, suggesting a deactivation process of the catalysts in the olefin polymerisation reactions. In an additional effort to model the catalytic species, stoichiometric reactions between the methyl derivatives TiCpRx[1,2‐C6H4(NR′)2]Me and solid methylaluminoxane (MAO) were studied by NMR spectroscopy. Monitoring of these reactions revealed the formation of zwitterionic species depending on the nature of the solvent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Monocyclopentadienyl Phenoxido–Amino and Phenoxido–Amido Titanium Complexes: Synthesis, Characterisation, and Reactivity of Asymmetric Metal Centre Derivatives

“…The methylated com-pound decomposes at room temperature, and evolution by ligand transfer from titanium to aluminum probably occurred. [15] The decreased trend in activity observed as the temperature is raised for these precatalysts in the α-olefin polymerisation might be due to a catalytically active decomposition process through ligand abstraction by MAO, which may cause a partial or complete loss of the ligand resulting in one or more inactive species for α-olefin polymerisation. [15,37] Compounds 3c and 3d are stabilised by coordination of phenoxido-amido ligands with higher N-donor ability compared with 3a and 4a, suggesting a more stable methyltitanium species obtained under these polymerisation reaction conditions.…”

“…Given our interest in the polymerisation chemistry of group 4 monocyclopentadienyl diamido [15] or dialkoxido [10,11] metal complexes, we undertook preliminary studies on α-olefin polymerisation process for these monocyclopentadienyl phenoxido-amido compounds in the presence of sMAO as cocatalyst. [36] Ethylene polymerisation was investigated by using 50 mL total volume of toluene with 10 -4 mol of catalyst and a 400 sMAO/Ti molar ratio at 1 atm pressure for 15 min.…”

“…In recent years, we have reported the synthesis of a series of cyclopentadienyl titanium complexes containing chelating dialkoxido [10][11][12] and diamido [13,14] ligands and studied the nature of the catalytic species in the α-olefin polymerisation processes generated by the reaction of these complexes with aluminum and boron reagents as cocatalyst. [15] In this paper we report the synthesis and characterisation of secondary phenol-amine compounds RЈNHCH 2 (3,5-R 2 C 6 H 2 -2-OH) obtained from the phenol-imine derivatives RЈN=CH(3,5-R 2 C 6 H 2 -2-OH) and tertiary phenol-amine compounds tBuN(R)CH 2 (3,5-tBu 2 C 6 H 2 -2-OH) derived from the corresponding benzoxazine derivatives. Phenolamine molecules are used as ligand precursors to synthesise phenoxido-amido TiCp R [RЈNCH 2 (3,5-tBu 2 C 6 H 2 -2-O)]Cl and phenoxido-amino TiCp[tBuNHCH 2 (3,5-tBu 2 C 6 H 2 -2-O)]Cl 2 titanium derivatives.…”

Studies on the active species in olefin polymerisation generated from phenoxo-amido titanium “chiral-at-metal” compounds

“…We are interested in the polymerisation behaviour of group 4 monocyclopentadienyl diamido [31] or dialkoxo [26,27] 7) were studied as ethylene and propylene polymerisation precatalyst systems under various conditions. The observed results show averages of two or, in some cases, more polymerisation runs, which showed good reproducibility.…”

“…Previously, we have reported the synthesis of a series of cyclopentadienyl titanium complexes containing chelating dialkoxo [26e28] and diamido [29,30] ligands and studied the nature of the catalytic species in the a-olefin polymerisation processes generated by the reaction of these complexes with aluminium and boron reagents as cocatalyst [31]. As a part of a broad research programme aimed at investigating the catalytic performance of compounds with these characteristics, combining a cyclopentadienyl group and a chelating ligand, we have also recently reported the synthesis and polymerisation studies of various phenoxo-amido group 4 metal complexes stabilised by an unsubstituted cyclopentadienyl ligand (h 5 -C 5 H 5 ) [32].…”