AUTHOR=Zou Xue-Ru , Chang Yu-Ning , Huang Kuo-Wei , Liang Lan-Chang 

TITLE=Enhanced Reactivity of Aluminum Complexes Containing P-Bridged Biphenolate Ligands in Ring-Opening Polymerization Catalysis

JOURNAL=Frontiers in Chemistry

VOLUME=6

YEAR=2018

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2018.00607

DOI=10.3389/fchem.2018.00607

ISSN=2296-2646

ABSTRACT=<p>Aluminum complexes containing [RP(O)(2-O-3,5-<italic>t</italic>Bu<sub>2</sub>C<sub>6</sub>H<sub>2</sub>)<sub>2</sub>]<sup>2−</sup> [R = <italic>t</italic>Bu (<bold>3a</bold>), Ph (<bold>3b</bold>)] have been synthesized, structurally characterized, and their reactivity studied in comparison with those of their [RP(2-O-3,5-<italic>t</italic>Bu<sub>2</sub>C<sub>6</sub>H<sub>2</sub>)<sub>2</sub>]<sup>2−</sup> [R = <italic>t</italic>Bu (<bold>2a</bold>), Ph (<bold>2b</bold>)] analogs. Treating AlMe<sub>3</sub> with one equiv of H<sub>2</sub>[<bold>3a-b</bold>] in THF at 0°C affords quantitatively [<bold>3a-b</bold>]AlMe, subsequent reactions of which with benzyl alcohol in THF at 25°C generate {[<bold>3a-b</bold>]Al(μ<sub>2</sub>-OCH<sub>2</sub>Ph)}<sub>2</sub>. The methyl [<bold>3a-b</bold>]AlMe and the benzyloxide {[<bold>3a-b</bold>]Al(μ<sub>2</sub>-OCH<sub>2</sub>Ph)}<sub>2</sub> are all active for catalytic ring-opening polymerization (ROP) of ε-caprolactone and <italic>rac</italic>-lactide (<italic>rac</italic>-LA). Controlled experiments reveal that {[<bold>3a</bold>]Al(μ<sub>2</sub>-OCH<sub>2</sub>Ph)}<sub>2</sub> is competent in living polymerization. Kinetic studies indicate that [<bold>3a</bold>]AlMe, in the presence of benzyl alcohol, catalyzes ROP of <italic>rac</italic>-LA at a rate faster than [<bold>3b</bold>]AlMe and [<bold>2a</bold>]AlMe(THF) by a factor of 1.8 and 23.6, respectively, highlighting the profound reactivity enhancement in ROP catalysis by varying the P-substituents of these biphenolate complexes of aluminum.</p>