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

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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

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Macaranas, J. A., Luke, A. M., Mandal, M., Neisen, B. D., Marell, D. J., Cramer, C., & Tolman, W. B. (2018). Sterically Induced Ligand Framework Distortion Effects on Catalytic Cyclic Ester Polymerizations. Inorganic chemistry, 57(6), 3451-3457. https://doi.org/10.1021/acs.inorgchem.8b00250