Investigations Into the Design of Electronically Responsive Ligands Open Access

Bothwell, Jason (2013)

Permanent URL: https://etd.library.emory.edu/concern/etds/h128nf30k?locale=en
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Abstract

The propensity for nickel to undergo sequential one-electron processes has been central in the key elementary steps comprising cross-coupling reactions. Here, we describe our progress in developing a new class of ligands aimed towards facilitating two-electron reactivity at the metal center, reactivity more akin to palladium catalysis. Through intermolecular studies, we show the requisite for stabilizing Ni0 is a nitroarene or an electron-poor olefin (e.g. maleimide or an α, β-unsaturated carbonyl). Stoichiometric studies have shown nitroarenes lead to the irreversible formation of nickel-black and free ligand, whereas isolable complexes are observed with other ligands. The results of these studies provide the framework for the optimization of future generations of ligands. A comprehensive study on the reactivity of these Ni0 complexes remains to be explored.

Specific Aims

The first aim of this project is to study the reductive elimination of (tmeda)Ni(CH3)2 in the presence of various Π-accepting moieties and gain insight into the structure of the presumed (tmeda)Ni0(Π-acceptor) species. Following this, the design and synthesis of various ligands will begin in order to generate isolable Ni0 complexes. A study of the reactivity of these Ni0 complexes may provide insight into the breadth of transformations allowed with the complexes presented herein. If these studies are successful, we aim to provide a new class of catalysts for reactions abiding by the classic Ni0 / NiII or Pd0 / PdII catalytic cycle, with an emphasis placed on the elucidation of the respective reaction mechanisms.

Table of Contents

1. Introduction

1

1.1 Differences Between Nickel and Palladium Catalysis

2

1.2 Mechanistic Studies.

4

1.3 Oxidatively-Induced Reductive Elimination

8

1.4 Project Inspiration

9

1.5 Electronically Responsive Ligands

10

2. Results and Discussion

11

2.1 Synthesis and Reactivity of NiL2X2 Species

12

2.2 Synthesis of L2NiII(Ph)(Cl) Species

14

2.3 Generation of L2NiII(CH3)2 and Intermolecular Studies

16

2.4 Ligand Development

21

3. Preliminary Metallation Studies

24

4. Conclusions

25

5. Experimental Section

27

6. References

79

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