Sterically Induced Ligand Framework Distortion Effects on Catalytic Cyclic Ester Polymerizations

Joahanna A. Macaranas, Anna M. Luke, Mukunda Mandal, Benjamin D. Neisen, Daniel J. Marell, Chris Cramer, William B. Tolman

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Aluminum alkoxide complexes supported by salen ligands [salen = N,N′-bis(salicylaldimine)-2-methylpropane-1,2-diamine or N,N′-bis(salicylaldimine)-2,2-dimethylpropane-1,3-diamine] with o-adamantyl substituents have been synthesized and investigated for the polymerization of ϵ-caprolactone. Geometric analysis of the catalysts used for the reaction reveals the metal coordination geometries to be intermediate between square-pyramidal and trigonal-bipyramidal. A detailed kinetic study accompanied by density functional theory modeling of key mechanistic steps of the reaction suggest that, in addition to the length of the backbone linker, the o-aryl substituents have a significant impact on the catalyst's reactivity. Bulky ortho substituents favorably distort the precatalyst geometry and thereby foster the achievement of the rate-limiting transition-state geometry at low energetic cost, thus accelerating the reaction.

Original languageEnglish (US)
Pages (from-to)3451-3457
Number of pages7
JournalInorganic chemistry
Volume57
Issue number6
DOIs
StatePublished - Mar 19 2018

Bibliographical note

Funding Information:
Funding for this project was provided by the Center for Sustainable Polymers at the University of Minnesota, a National Science Foundation (NSF)-supported Center for Chemical Innovation (Grant CHE-1413862). The X-ray diffraction experiments were performed using a crystal diffractometer acquired through NSF-MRI Award CHE-1229400. The authors acknowledge the MSI at the University of Minnesota for providing resources that contributed to the research results reported within this paper. We also thank Dr. Manuel Ortuño for helpful discussions on computational modeling. NMR instrumentation was supported by the Office of the Vice President of Research, College of Science and Engineering, and the Department of Chemistry at the University of Minnesota; the Bruker HD NMR spectrometer was supported by the Office of the Director, National Institutes of Health under Award S10OD011952. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Funding Information:
This project was provided by the Center for Sustainable Polymers at the University of Minnesota, a National Science Foundation (NSF)-supported Center for Chemical Innovation (Grant CHE-1413862). The X-ray diffraction experiments were performed using a crystal diffractometer acquired through NSF-MRI Award CHE-1229400. The authors acknowledge the MSI at the University of Minnesota for providing resources that contributed to the research results reported within this paper.

Publisher Copyright:
© 2018 American Chemical Society.

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