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Reductive elimination of alkylamines and ethers: reactions of bisphosphine-ligated palladium(II) complexes

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Title: Reductive elimination of alkylamines and ethers: reactions of bisphosphine-ligated palladium(II) complexes
Author(s): Marquard, Seth L.
Director of Research: Hartwig, John F.
Doctoral Committee Chair(s): Hartwig, John F.
Doctoral Committee Member(s): Rauchfuss, Thomas B.; White, M C.; Shapley, Patricia A.
Department / Program: Chemistry
Discipline: Chemistry
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Reductive Elimination Alkylamines Alkyl ethers Palladium
Abstract: The reductive elimination reactions detailed in this dissertation provide experimental insight into the mechanism of reductive elimination to form the C(sp3)-N bond of benzylamines and the C(sp3)-O bond of benzyl ethers. The stereochemical outcome of the reaction indicates an ionic pathway, but the process lacks many of the effects of electronic and solvent perturbations that typically signal an ionic intermediate. We propose that reductive elimination from benzylpalladium(II) amido and aryloxide complexes occurs by dissociation of the amido or aryloxide ligand, followed by nucleophilic attack on the benzyl ligand. The proposed ionic mechanism is more akin to the reductive elimination reactions that occur from high-valent Pt(IV) and Ni(III) complexes than reductive elimination reactions that occur from other Pd(II) complexes. Our data indicate that substantial differences exist between reductive eliminations to form the C(sp3) bonds in ethers and amines from palladium(II). We prepared alkylpalladium(II) amido complexes to study the C(sp3)-N reductive elimination reaction from complexes containing a non-benzylic hydrocarbyl ligand. We investigated a series of alkylpalladium amido complexes and observed reductive elimination occurs from bisphosphine-ligated neopentylpalladium amido complexes in low yield. Reductive elimination from neopentylpalladium amido complexes occurs most likely by a concerted reductive elimination reaction, and is favored by the increased steric bulk of the neopentyl ligand. We also investigated azametallacyclic palladium complexes with a norbornyl hydrocarbyl ligand, and observed reductive elimination occurs to form a norbornyl indoline product. We found that the yield was slightly improved over neopentylpalladium complexes, but that the yield of reductive elimination was low. Finally we investigated non-metallacyclic complexes containing a norbornyl hydrocarbyl ligand. We discovered that reductive elimination occurs in moderate yield, and the reductive elimination product ratio indicates a balance between a concerted and an ionic mechanism. The data presented in this dissertation demonstrate that C(sp3)-N reductive elimination from benzylpalladium(II) and alkylpalladium(II) complexes can occur. We propose an ionic mechanism for the formation of benzylamines and benzyl ethers by reductive elimination from benzylpalladium(II) complexes. Reductive elimination from neopentyl and metallacyclicpalladium(II) complexes likely occurs by a concerted mechanism, demonstrating the importance of steric bulk and metal geometry, respectively. Finally, reductive elimination from non-metallacyclic norbornylpalladium(II) complexes indicates that a concerted and ionic mechanism may occur simultaneously. Although the yield of the alkylamine products is low, the observation that C(sp3)-N reductive elimination occurs from the alkylpalladium complexes provides the first step toward developing a synthetically useful reaction for the formation of C(sp3)-heteroatom bonds from low-valent group 10 complexes without the addition of an oxidant.
Issue Date: 2012-02-06
URI: http://hdl.handle.net/2142/29806
Rights Information: Copyright 2011 Seth L. Marquard
Date Available in IDEALS: 2012-02-06
Date Deposited: 2011-12
 

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