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Title: Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism.

The scope and mechanism of thermodynamically leveraged ester RC(O)O-R' bond hydrogenolysis by tandem metal triflate + supported Pd catalysts are investigated both experimentally and theoretically by DFT and energy span analysis. This catalytic system has a broad scope, with relative cleavage rates scaling as, tertiary 4 secondary 4 primary ester at 1 bar H-2, yielding alkanes and carboxylic acids with high conversion and selectivity. Benzylic and allylic esters display the highest activity. The rate law is nu = k[M(OTf )(n)](1)[ester](0)[H-2](0) with an H/D kinetic isotope effect = 6.5 +/- 0.5, implying turnover-limiting C-H scission following C-O cleavage, in agreement with theory. Intermediate alkene products are then rapidly hydrogenated. Applying this approach with the very active Hf(OTf)(4) catalyst to bio-derived triglycerides affords near-quantitative yields of C-3 hydrocarbons rather than glycerol. From model substrates, it is found that RC(O)O-R' cleavage rates are very sensitive to steric congestion and metal triflate identity. For triglycerides, primary/external glyceryl CH2-O cleavage predominates over secondary/internal CH-O cleavage, with the latter favored by less acidic or smaller ionic radius metal triflates, raising the diester selectivity to as high as 48% with Ce(OTf)(3).
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Publication Date:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Energy & Environmental Science; Journal Volume: 9; Journal Issue: 2
Royal Society of Chemistry
Research Org:
Argonne National Laboratory (ANL)
Sponsoring Org:
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; USDOE Energy Frontier Research Center - Institute for Atom-Efficient Chemical Transformation; National Science Foundation (NSF); USDOE Office of Science - National Energy Research Scientific Computing Center (NERSC)
Country of Publication:
United States