Mechanistic Study of Isotactic Poly(propylene oxide) Synthesis using a Tethered Bimetallic Chromium Salen Catalyst.
Bryce M LipinskiKatherine L WalkerNaomi E ClaymanLilliana S MorrisTimothy M E JugovicAllison G RoesslerYutan D Y L GetzlerSamantha N MacMillanRichard N ZarePaul M ZimmermanRobert M WaymouthGeoffrey W CoatesPublished in: ACS catalysis (2020)
Initial catalyst dormancy has been mitigated for the enantioselective polymerization of propylene oxide using a tethered bimetallic chromium(III) salen complex. A detailed mechanistic study provided insight into the species responsible for this induction period and guided efforts to remove them. High-resolution electrospray ionization-mass spectrometry and density functional theory computations revealed that a μ-hydroxide and a bridged 1,2-hydroxypropanolate complex are present during the induction period. Kinetic studies and additional computation indicated that the μ-hydroxide complex is a short-lived catalyst arrest state, where hydroxide dissociation from one metal allows for epoxide enchainment to form the 1,2-hydroxypropanolate arrest state. While investigating anion dependence on the induction period, it became apparent that catalyst activation was the main contributor for dormancy. Using a 1,2-diol or water as chain transfer agents (CTAs) led to longer induction periods as a result of increased 1,2-hydroxyalkanolate complex formation. With a minor catalyst modification, rigorous drying conditions, and avoiding 1,2-diols as CTAs, the induction period was essentially removed.
Keyphrases
- reduced graphene oxide
- ionic liquid
- room temperature
- metal organic framework
- highly efficient
- high resolution
- mass spectrometry
- density functional theory
- carbon dioxide
- gold nanoparticles
- visible light
- cell cycle
- computed tomography
- molecular dynamics
- liquid chromatography
- magnetic resonance
- single cell
- diffusion weighted imaging