3 years ago

Cationic Scandium Anisyl Species in Styrene Polymerization Using Anisole and N,N-Dimethyl-o-toluidine as Chain-Transfer Agents

Cationic Scandium Anisyl Species in Styrene Polymerization Using Anisole and N,N-Dimethyl-o-toluidine as Chain-Transfer Agents
Atsushi Yamamoto, Yang Yang, Masayoshi Nishiura, Zhaomin Hou
This work aimed to clarify the involvement of a cationic scandium anisyl species in the scandium-catalyzed chain-transfer polymerization of styrene using anisole as a chain-transfer agent (CTA) as well as its behavior in the presence of N,N-dimethyl-o-toluidine. The reaction of anisole with the catalyst precursor [(C5Me4SiMe3)Sc(CH2C6H4NMe2-o)][B(C6F5)4] (2) generated by the reaction of (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 (1) with [Ph3C][B(C6F5)4] gave the structurally characterizable anisole-coordinated ion-pair complex [(C5Me4SiMe3)Sc(CH2C6H4NMe2-o)(C6H5OMe)][B(C6F5)4] (3). The aminobenzyl unit in 3 remained intact even in the presence of an excess amount of anisole. The formation of an anisyl species from 3 was not observed by 1H NMR. However, the polymerization of styrene by 3 at either room temperature or 70 °C yielded the anisyl-end-functionalized syndiotactic polystyrene (sPS) as a major product in addition to the dimethylaminobenzyl-end-capped sPS. These results suggest that an equilibrium between the aminobenzyl species 3 and a scandium anisyl species should exist, although the latter was not detected by 1H NMR. The reaction of the half-sandwich scandium bis(anisyl) complex (C5Me4SiMe3)Sc(C6H4OMe-o)2 (4) with 1 equiv of [Ph3C][B(C6F5)4] in THF afforded the THF-coordinated cationic scandium monoanisyl complex [(C5Me4SiMe3)Sc(C6H4OMe-o)(thf)2][B(C6F5)4] (5), which upon reaction with HMPA gave the structurally characterizable HMPA-coordinated analogue [(C5Me4SiMe3)Sc(C6H4OMe-o)(hmpa)2][B(C6F5)4] (6). The 4/[Ph3C][B(C6F5)4] combination in toluene showed high activity for styrene polymerization, selectively yielding the anisyl-end-functionalized sPS. In addition to anisole, N,N-dimethyl-o-toluidine was also found to serve as an efficient CTA for the polymerization of styrene by 1/[Ph3C][B(C6F5)4], which selectively afforded the aminobenzyl-functionalized sPS.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00526

DOI: 10.1021/acs.organomet.7b00526

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