Electric Literature of 52409-22-0, A catalyst don’t appear in the overall stoichiometry of the reaction it catalyzes, but it must appear in at least one of the elementary reactions in the mechanism for the catalyzed reaction. 52409-22-0, Name is Pd2(DBA)3, molecular formula is C51H42O3Pd2. In a Article£¬once mentioned of 52409-22-0
Mechanistic investigations on asymmetric N-H insertion of amines catalyzed by palladium-chiral guanidine complex
The mechanism and stereoselectivity of the asymmetric N-H insertion reactions between alpha-diazocarbonyl compounds and amines mediated by palladium-chiral guanidine complexes were investigated at the BP86-D3(BJ)/def2TZVP (SMD, CH2Cl2)//BP86-D3(BJ)/def2SVP (SMD, CH2Cl2) level at 303 K. The non-catalytic reaction occurred through a stepwise mechanism, with a high activation barrier of 56.4 kcal mol?1. Good linear correlations between the global nucleophilicity index (N) of amine, Hammett substituent constants (sigmaP), and the activation energy barriers (DeltaG?) were found. The Pd(0)-guanidine-catalyzed reaction consisted of three continuous steps, including: (i) generation of Pd-carbene intermediate by dinitrogen loss from alpha-diazoesters substrate, (ii) formation of C?N bond, and (iii) 1,2-H transfer by metal-associated ylide, accompanying with the regeneration of catalyst. A water molecule accelerated the final H-transfer by constructing hydrogen bonding network. The cyclohexyl group in ligand provided sufficient steric shielding around Pd-carbene intermediate from the re-face attack by amines. The combination of the hydrogen bonding orientation of amide moiety of guanidine ligand, as well as the steric repulsion between the ester group of alpha-diazoester substrate and bulky ?CH(Ph)2 group in ligand played an important role in controlling the stereoselectivity, affording the predominant S-configuration product observed in experiment. Introducing one aromatic ring to chiral backbone of the guanidine ligand enhanced the enantiodifferentiation of products by increasing the difference of strain energy (DeltaDeltaEstrain) of Pd-carbene moiety along two competing pathways. Different from Pd(0)-catalyst, the Pd(II)-chiral guanidine complex accelerated N-H insertion reaction via Lewis acid catalysis. In this process, the formation of free ylide in the reaction led to low ee. These results were in good agreement with experimental observations.
Balanced chemical reaction does not necessarily reveal either the individual elementary reactions by which a reaction occurs or its rate law.Electric Literature of 52409-22-0. In my other articles, you can also check out more blogs about 52409-22-0
Reference£º
Chapter 1 An introduction to palladium catalysis,
Palladium/carbon catalyst regeneration and mechanical application method