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Inorganics 2017, 5(4), 87; https://doi.org/10.3390/inorganics5040087

The Mechanism of Rh-Catalyzed Transformation of Fatty Acids to Linear Alpha olefins

Department of Chemistry, University of Bergen, Allégaten 41, N-5007 Bergen, Norway
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Received: 15 October 2017 / Revised: 23 November 2017 / Accepted: 29 November 2017 / Published: 4 December 2017
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Abstract

Linear alpha olefins (LAOs) are key commodity chemicals and petrochemical intermediates that are currently produced from fossil resources. Fatty acids are the obvious renewable starting material for LAOs, which can be obtained via transition-metal-catalyzed decarbonylative dehydration. However, even the best catalysts that have been obtained to date, which are based on palladium, are not active and stable enough for industrial use. To provide insight for design of better catalysts, we here present the first computationally derived mechanism for another attractive transition-metal for this reaction, rhodium. By comparing the calculated mechanisms and free energy profiles for the two metals, Pd and Rh, we single out important factors for a facile, low-barrier reaction and for a stable catalyst. While the olefin formation is rate limiting for both of the metals, the rate-determining intermediate for Rh is, in contrast to Pd, the starting complex, (PPh3)2Rh(CO)Cl. This complex largely draws its stability from the strength of the Rh(I)–CO bond. CO is a much less suitable ligand for the high-oxidation state Rh(III). However, for steric reasons, rhodium dissociates a bulkier triphenylphosphine and keeps the carbonyl during the oxidative addition, which is less favorable than for Pd. When compared to Pd, which dissociates two phosphine ligands at the start of the reaction, the catalytic activity of Rh also appears to be hampered by its preference for high coordination numbers. The remaining ancillary ligands leave less space for the metal to mediate the reaction. View Full-Text
Keywords: decarbonylative dehydration; DFT; catalysis; palladium; rhodium; renewable resources decarbonylative dehydration; DFT; catalysis; palladium; rhodium; renewable resources
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Eliasson, S.H.H.; Chatterjee, A.; Occhipinti, G.; Jensen, V.R. The Mechanism of Rh-Catalyzed Transformation of Fatty Acids to Linear Alpha olefins. Inorganics 2017, 5, 87.

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