Journal
CHEMCATCHEM
Volume 13, Issue 5, Pages 1317-1325Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cctc.202001411
Keywords
Partial transfer hydrogenation; E-selective alkyne hydrogenation; deuterated alkenes; ruthenium; paraformaldehyde
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Funding
- MIWF-NRW (NRW-returnee program)
- Heisenberg-Program (DFG)
- COST Action C H Activation in Organic Synthesis (CHAOS)
- Ernst-Haage-Prize of the Max-Planck-Institute for Chemical Energy Conversion
- Projekt DEAL
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E-alkenes were synthesized with up to 100% E/Z selectivity via ruthenium-catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer-hydrogenation conditions. The use of paraformaldehyde as a safe and cheap solid hydrogen carrier, along with water, for transfer-hydrogenation of alkynes was optimized with the binuclear [Ru(p-cymene)Cl-2](2) complex and BINAP ligand. Mechanistic investigations revealed that the E-selectivity in this reaction is due to the fast Z to E isomerization of the formed alkenes.
E-alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium-catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer-hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer-hydrogenation of alkynes. Optimization reactions showed the best results for the commercially available binuclear [Ru(p-cymene)Cl-2](2) complex as pre-catalyst in combination with 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BINAP) as ligand (1 : 1 ratio per Ru monomer to ligand). Mechanistic investigations showed that the origin of E-selectivity in this reaction is the fast Z to E isomerization of the formed alkenes. Mild reaction conditions plus the use of cheap, easily available and safe materials as well as simple setup and inexpensive catalyst turn this protocol into a feasible and promising stereo complementary procedure to the well-known Z-selective Lindlar reduction in late-stage syntheses. This procedure can also be used for the production of deuterated alkenes simply using d(2)-paraformaldehyde and D2O mixtures.
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