Group 4 metal and vanadium bis(phenolato) complexes : synthesis, structure and olefin polymerisation activity

The first objectives of this work were to obtain a enantiomerically pure [Ti{OSSO}X2] polymerisation catalyst and to use it to determine at what degree of polymerisation a polystyrene chain becomes cryptochiral. The resolution of the Delta and Lambda enantiomers of a [Ti{2,2’-(OC6H2-6-tBu-4-Me)2SC2H4S}X2] was attempted via chiral template synthesis. Complexation of the achiral bis(phenol) to a (R)-1,1’-bi-2-naphthoxy titanium species was not diastereoselective and reaction with 3,3’-substituted templates did not proceed at all. Surprisingly, the partial hydrolysis of [Ti{(R)-C20H12O2}{2,2’-(OC6H2-6-tBu-4-Me)2SC2H4S}] in acetone solution did proceed diastereoselectively to give a homochiral dinuclear species, bridged by a binaphtoxy moiety and by an oxygen atom. A chiral template can be abandoned if an [OSSO]-type ligand is developed with a chiral source that predetermines the configuration with which the ligand coordinated to the metal centre. Therefore, trans-1,2-dithiacyclohexanediyl-bridged bis(phenols) were synthesised in three steps. Nucleophilic attack of an hydroxyarenethiolate on cyclohexene oxide, followed by chlorination, and substitution by a second equivalent of the thiolate gave exclusively 1,2-trans bis(phenols) via anchimeric assistance. The chiral bis(phenols) could be resolved either by classical resolution with (1S)-camphorsulfonyl chloride or by preparative (chiral) HPLC of the diastereomers and enantiomers respectively. Reaction of trans-1,2-dithiacyclohexanediyl-bridged [OSSO]-type ligands with TiX4 proceeds diastereoselectively, thus giving access to enantiomerically pure precatalysts. In contrast to 1,4-dithiabutanediyl-bridged [OSSO] ligands, [2,2’-(HOC6H2-6-R1-4-R2)2SC6H10S] are so efficient in directing and maintaining the configuration of their respective titanium complexes that large ortho-substituents are not required. To investigate cryptochiality, low molecular weight oligostyrenes were produced by optically active titanium catalysts. The molecular weight during polymerisation could be controlled by addition of 1-hexene as a chain-transfer agent. Depending on the substitution of the ligand, 1-hexene-terminated oligostyrenes with a minimum molecular weight of 800-1300 g mol-1 could be obtained. Oligomers with a polymerisation degree of up to ca. 45 show optical activity. Reaction of racemic [2,2’-(HOC6H2-6-tBu-4-Me)2SC6H10S] with VOCl3 afforded a C1-symmetrical bis(phenolato) vanadium(V) complex, which spontaneously resolves upon crystallisation. iastereoselectivity is the same as for titanium complexes. When activated with MAO, [V{2,2’-(OC6H2-6-tBu-4-Me)2SC6H10S}OCl] did not polymerise propene or styrene, but was highly active for the polymerisation of ethene. Using similar nucleophilic ring-opening methodology as for the cyclohexanediyl-bridged [OSSO]-type ligands, a family of trans-1,2-azathiacyclohexanediyl-bridged [OSNO]-type bis(phenols) was synthesised. In this fashion [2,2’-(HOC6H2-6-tBu-4-R1)2SC6H10NR2] (R1 = tBu, Me; R2 = H, Me), [2,2’-(HOC6H2-4,6-tBu2)2SC6H10N=CH] and [2,2’-(HOC6H2-4,6-tBu2)2SC6H10NHCH2] were obtained. Although for such asymmetrical ligands many isomers are possible, formation of titanium complexes of the first ligands proceeded with perfect diastereoselectively; the half-salen and half-salan hybrids gave a mixture of two isomers (Scheme S.4). All titanium complexes were configurationally stable in solution up to 100°C. For [Ti{2,2’-(HOC6H2-6-tBu-4-R1)2SC6H10NR2}X2] (X = Cl, OiPr), cis-alpha and cis-beta2 coordination modes of the ligand were observed, depending on the nitrogen substituent and on the auxiliary ligand. In [Ti{2,2’-(HOC6H2-4,6-tBu2)2SC6H10N=CH}Cl2] and [Ti{2,2’-(HOC6H2-4,6-tBu2)2SC6H10NHCH2}Cl2] both configurations coexist and did not interconvert at elevated temperatures, but HCl catalysed the isomerization from cis-alpha to cis-beta2. Upon activation with methylaluminoxane, [Ti{OSNO}X2] complexes were moderately active in the polymerization of styrene and gave trace activity in the polymerization of 1-hexene, thus combining the worst polymerisation properties of their parent ligands, rather than the best. A different way to influence polymerisation properties is to investigate the effect of the linkage between the arene groups. For group 4 [ONNO]-type catalysts, only salen- and salan-type complexes are known; 1,4-diazabutanediyl-bridged bis(phenolato) species were not examined. These ligands were synthesised by reaction of the 3,5-tBu2-catechol with ethylene diamine and optional methylation of the nitrogen atoms. With the appropriate metal precursors MX4 (M = Ti, Zr, Hf) a series of group 4 metal dichloro and di(isopropoxy) complexes [M{2,2’-(OC6H2-4,6-tBu2)2NRC2H4NR}X2] (Ti: R = H, Me; X = Cl, OiPr; Zr, Hf: X = Cl; R = Me) was obtained. Whilst [ONNO] zirconium and hafnium dichlorides gave configurationally stable cis-alpha species up to 100°C, titanium [ONNO] complexes gave both cis-alpha and cis-beta isomers (Scheme S.5). The configuration of [Ti{2,2’-(OC6H2-4,6-tBu2)2MeNC2H4NMe}Cl2] and [Ti{2,2’-(OC6H2-4,6-tBu2)2HNC2H4NH}Cl2] changed from cis-beta to cis-alpha at elevated temperatures. Upon activation with methylaluminoxane, all precatalysts polymerised styrene with modest activity. Good (M = Ti) to excellent (M = Zr, Hf) activity in the atactic polymerization of 1-hexene was observed.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2009

Author dc:creator

• Meppelder, Geert Johannes Marinus

Contributors dc:contributor

• Okuda, Jun

• info:eu-repo/classification/ddc/540
• Metallorganische Chemie
• Polymerisation
• Styrol
• Chemie
• organometallic chemistry
• chirality
• olefin polymerisation
• styrene

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124555%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:63097