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Phenolic 3° Phosphine Oxides as a Class of Metal-Free Catalysts for the Activation of C–O Bonds in Aliphatic Alcohols: Direct Synthesis of Catalyst Candidates, and Kinetic Studies

Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave., Pittsburgh, PA 15282, USA
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Academic Editors: Jianbing (Jimmy) Jiang and Philip Mountford
Inorganics 2022, 10(3), 35; https://doi.org/10.3390/inorganics10030035
Received: 6 January 2022 / Revised: 6 March 2022 / Accepted: 7 March 2022 / Published: 11 March 2022
(This article belongs to the Special Issue Bond Activation and Catalysis Using Main-Group Elements)
It was recently reported that a (2-hydroxybenzyl)phosphine oxide (2-HOBPO) can serve as a phosphorus-centered catalyst for the stereo-invertive coupling of aliphatic alcohols and acidic pronucleophiles (akin to a Mitsunobu reaction, but without additional reagents). Herein, we report an improved synthesis, which provides direct access to systematically varied 2-HOBPOs in a single step from commercially available precursors (salicylaldehydes and secondary phosphines). The efficiency and generality of the synthetic method enabled limited structure–activity relationship (SAR) studies, from which it was determined that substituents on both the phenolic and phosphine oxide portions can exert significant influence on the turnover frequency (TOF) of each catalyst. Importantly, for all catalytically active 2-HOBPOs examined, the molecularity of catalyst in the rate law of the alcohol coupling was determined to be <1. Thus, for high catalyst loadings, differences in catalytic activity between 2-HOBPOs appear to be dominated by differences in catalytic auto-inhibition, while for low catalyst loadings, differences are attributed to inherent differences in the energetic span of the catalytic cycle, ignoring off-cycle species, in good agreement with density functional theory (DFT) modeling at the ωB97X-D/6-311G(d,p) level. View Full-Text
Keywords: phosphine oxide; alcohol activation; Mitsunobu reaction; organocatalysis phosphine oxide; alcohol activation; Mitsunobu reaction; organocatalysis
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MDPI and ACS Style

Martin, M.A.; Brown, S.L.; Beres, D.R.; Frederic, W.M.; Banks, A.M.; Bloomfield, A.J. Phenolic 3° Phosphine Oxides as a Class of Metal-Free Catalysts for the Activation of C–O Bonds in Aliphatic Alcohols: Direct Synthesis of Catalyst Candidates, and Kinetic Studies. Inorganics 2022, 10, 35. https://doi.org/10.3390/inorganics10030035

AMA Style

Martin MA, Brown SL, Beres DR, Frederic WM, Banks AM, Bloomfield AJ. Phenolic 3° Phosphine Oxides as a Class of Metal-Free Catalysts for the Activation of C–O Bonds in Aliphatic Alcohols: Direct Synthesis of Catalyst Candidates, and Kinetic Studies. Inorganics. 2022; 10(3):35. https://doi.org/10.3390/inorganics10030035

Chicago/Turabian Style

Martin, Matthew A., Sadie L. Brown, Danielle R. Beres, Wrebekah M. Frederic, Ashley M. Banks, and Aaron J. Bloomfield. 2022. "Phenolic 3° Phosphine Oxides as a Class of Metal-Free Catalysts for the Activation of C–O Bonds in Aliphatic Alcohols: Direct Synthesis of Catalyst Candidates, and Kinetic Studies" Inorganics 10, no. 3: 35. https://doi.org/10.3390/inorganics10030035

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