852621-01-3

Upstream product

• 108-31-6 maleic anhydride 
• 64537-36-6 (η2,η2-norbornadiene)(η2-maleic anhydride)palladium(0) 
• 141556-45-8 1,3-bis(mesityl)imidazolium chloride 
• 78192-91-3 [N,N′-1,2-ethanediylidenebis[2-methyl-2-propanamine-κN]][(3,4-η)-2,5-furandione]-palladium 
• 75-05-8 acetonitrile 

Relevant academic research and scientific papers

Mechanism of Pd(NHC)-catalyzed transfer hydrogenation of alkynes

The transfer semihydrogenation of alkynes to (Z)-alkenes shows excellent chemo- and stereoselectivity when using a zerovalent palladium(NHC)(maleic anhydride)-complex as precatalyst and triethylammonium formate as hydrogen donor. Studies on the kinetics under reaction conditions showed a broken positive order in substrate and first order in catalyst and hydrogen donor. Deuterium-labeling studies on the hydrogen donor showed that both hydrogens of formic acid display a primary kinetic isotope effect, indicating that proton and hydride transfers are separate rate-determining steps. By monitoring the reaction with NMR, we observed the presence of a coordinated formate anion and found that part of the maleic anhydride remains coordinated during the reaction. From these observations, we propose a mechanism in which hydrogen transfer from coordinated formate anion to zerovalent palladium(NHC)(MA)(alkyne)-complex is followed by migratory insertion of hydride, after which the product alkene is liberated by proton transfer from the triethylammonium cation. The explanation for the high selectivity observed lies in the competition between strongly coordinating solvent and alkyne for a Pd(alkene)-intermediate.

Palladium-(N-heterocyclic carbene) hydrogenation catalysts

(Chemical Equation Presented) Low-valent palladium compounds with N-heterocyclic carbenes (NHCs) formed from [Pd(NHC)(η2-alkene) 2] (see example) are amazingly selective catalysts for the hydrogenation of several alkynes to Z alkenes. One such complex, [Pd{1,3-(2,6-diethylphenyl)imidazol-2-ylidene}], has been employed for the selective (95%) hydrogenation of 1-phenyl-1-propyne to (Z)-1-phenyl-1-propene.