New carbon-nitrogen bond-forming reactions of palladium

migratory insertion;reductive elimination;palladium;hydroamination

Hanley, Patrick

关键词: migratory insertion;    reductive elimination;    palladium;    hydroamination;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42411/Patrick_Hanley.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Here we report the synthesis of a series of palladium amido complexes that undergo some of the fundamental reactions of organometallic chemistry. We have discovered two new palladium mediated C-N bond-forming reactions: the migratory insertion of an unactivated alkene into a palladium-nitrogen bond and the reductive elimination of an alkylamine from a low-valent alkylpalladium amido complex. These reactions were previously proposed as steps in palladium catalyzed reactions, however, these are the first examples of isolated palladium complexes that undergo these C-N bond-forming reactions.The discovery of a series of amidopalladium complexes ligated by a cyclometallated benzylphosphine that react with unactivated alkenes is described. Kinetic and stereochemical analysis indicate that these complexes react by migratory insertion of an alkene into the Pd-N bond.In the presence of ethylene at low temperature (-65°C), an olefin adduct was observed by 31P and 13C NMR spectroscopy that, upon warming to -40 °C, reacted to generate enamines. The final products, enamines, are formed by migratory insertion and subsequent β-hydride elimination. In a subsequent report, reactions of a family of these complexes containing ancillary ligands having systematically varied electronic and steric properties allowed us to map the effect these properties have on the binding of the alkene and the rate of migratory insertion. Reactions of Pd-amides with functionalized vinylarenes were studied experimentally and computationally to determine the effect of the electronic properties of the alkene on the equilibrium for olefin binding and the rate of insertion.Alkene insertions into Pd-N bonds have been proposed in many catalytic reactions, and these are the first detailed studies of the steric and electronic effects on the migratory insertion step of the reaction of well-defined amido complexes with alkenes.In the final chapter, we describe the first alkylpalladium amido complexes that undergo C(sp3)-N bond-forming reductive elimination of alkylamines. Three-coordinate norbornylpalladium anilido complexes ligated by bulky monodentate N-heterocyclic carbene (NHC) ligands undergo thermal reductive elimination to generate alkylamine products.The stereochemistry of the norbornylamine product suggests that the reductive elimination occurs by a concerted mechanism.The experimentally determined free energy barrier for the reductive elimination of 26 kcal/mol is similar to the computed free energy barrier of 23.9 kcal/mol. Although the reductive elimination of alkylamine to form C(sp3)-N bonds has been proposed to occur in several palladium catalyzed reactions this is first example of isolated low-valent amido complex that undergoes these reactions. We also report preliminary results of reductive elimination of alkylamines from Pd-amido complex ligated by bulky monophosphine ligands.