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

ABSTRACT: Aluminum complexes containing [RP(O)(2-O-3,5-tBu₂C₆H₂)₂]^2- [R = tBu (3a), Ph (3b)] have been synthesized, structurally characterized, and their reactivity studied in comparison with those of their [RP(2-O-3,5-tBu₂C₆H₂)₂]^2- [R = tBu (2a), Ph (2b)] analogs. Treating AlMe₃ with one equiv of H₂[3a-b] in THF at 0°C affords quantitatively [3a-b]AlMe, subsequent reactions of which with benzyl alcohol in THF at 25°C generate {[3a-b]Al(?₂-OCH₂Ph)}₂. The methyl [3a-b]AlMe and the benzyloxide {[3a-b]Al(?₂-OCH₂Ph)}₂ are all active for catalytic ring-opening polymerization (ROP) of ?-caprolactone and rac-lactide (rac-LA). Controlled experiments reveal that {[3a]Al(?₂-OCH₂Ph)}₂ is competent in living polymerization. Kinetic studies indicate that [3a]AlMe, in the presence of benzyl alcohol, catalyzes ROP of rac-LA at a rate faster than [3b]AlMe and [2a]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.

SUBMITTER: Zou XR 

PROVIDER: S-EPMC6300491 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature