10.1021/ma501085c.s003
Bo Liu
Bo
Liu
Lei Li
Lei
Li
Guangping Sun
Guangping
Sun
Jingyao Liu
Jingyao
Liu
Meiyan Wang
Meiyan
Wang
Shihui Li
Shihui
Li
Dongmei Cui
Dongmei
Cui
3,4-Polymerization of
Isoprene by Using NSN- and NPN-Ligated
Rare Earth Metal Precursors: Switching of Stereo Selectivity and Mechanism
American Chemical Society
2014
Ph 2P NPNEt
2C
THF
ligand lithium salts
DFT
dialkyl complexes
Ln
Lu
NSN
CH 2SiMe n
2NH
Earth Metal Precursors
2014-08-12 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/3_4_Polymerization_of_Isoprene_by_Using_NSN_and_NPN_Ligated_Rare_Earth_Metal_Precursors_Switching_of_Stereo_Selectivity_and_Mechanism/2266660
The rare-earth metal complexes bearing
NSN-bidentate β-diimidosulfonate
ligands (RNSN<sup>dipp</sup>)Ln(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF)<sub><i>n</i></sub> (R = Ph, Ln = Lu (<b>1a</b>), <i>n</i> = 1, Y (<b>1b</b>), <i>n</i> = 2, Sc (<b>1c</b>), <i>n</i> = 1; R =
PhNMe<sub>2</sub>, Ln = Lu (<b>1d</b>), <i>n</i> =
1) were synthesized by treatment of the ion-pairs [Ln(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF)<sub><i>x</i></sub>][BPh<sub>4</sub>] with equimolar amount of the ligand lithium salts (RNSN<sup>dipp</sup>)Li(THF)<sub>2</sub> (NSN<sup>dipp</sup> = S(NC<sub>6</sub>H<sub>4</sub><sup><i>i</i></sup>Pr<sub>2</sub>-2,6)<sub>2</sub>). Addition reaction between lutetium tris(alkyl)s, Ln(Z)<sub>3</sub>(THF)<sub>n</sub> and NSN<sup>dipp</sup> gave the corresponding
dialkyl complexes (ZNSN<sup>dipp</sup>)Lu(Z)<sub>2</sub>(THF)<sub><i>n</i></sub> (Z = CH<sub>2</sub>SiMe<sub>3</sub>, <i>n</i> = 1 (<b>1e</b>); Z = <i>o</i>-CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>NMe<sub>2</sub>, <i>n</i> = 0
(<b>1f</b>)). Deprotonation of β-imidophosphonamido ligands
H–NPN<sup>dipp</sup> and H–NPN<sup>Et</sup> (NPN<sup>dipp</sup> = Ph<sub>2</sub>P(NC<sub>6</sub>H<sub>3</sub><sup><i>i</i></sup>Pr<sub>2</sub>-2,6)<sub>2</sub>, NPN<sup>Et</sup> = PPh<sub>2</sub>(NC<sub>6</sub>H<sub>3</sub><sup><i>i</i></sup>Pr<sub>2</sub>-2,6)(NC<sub>6</sub>H<sub>4</sub>-Et-2)) with
Lu(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>3</sub>(THF)<sub>2</sub> yielded
the corresponding dialkyl complexes (NPN<sup>dipp</sup>)Lu(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF) (<b>2</b>) and (NPN<sup>Et</sup>)Lu(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF) (<b>3</b>). All the complexes had been structurally well-defined,
and <b>1a</b>, <b>1b</b>, <b>1e, 2</b>, and <b>3</b> were further characterized by X-ray diffraction analysis
where the almost planar NSN rare-earth metal unit is <i>C</i><sub>s</sub> (or pseudo <i>C</i><sub>s</sub>) symmetry
with the two alkyl groups arranging on both sides and a coordinated
THF against it. Upon activation with [PhMe<sub>2</sub>NH][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] and Al<sup><i>i</i></sup>Bu<sub>3</sub>, all these complexes exhibited high 3,4-regioselectivity
(ranging from 91% to >99%) for the polymerization of isoprene.
Moreover,
the excellent isospecific selectivity up to <i>mmmm</i> >
99% have been achieved with complexes <b>1</b> depending on
the electronics of the sulfur substituents to give crystalline polyisoprene
with the highest <i>T</i><sub>m</sub> (170 °C) reported
to date. The NPN-bidentate β-imidophosphonamide ligated rare-earth
metal complexes provide both high syndio- and iso- 3,4-selectivities
(3,4 > 99%, <i>rr</i> = 66%, <i>mmmm</i> =
96%)
depending on the frameworks, steric environment and geometry of the
ligands. The regio- and stereo- selective mechanisms proceeded in
these systems were explicated by DFT simulation.