C-X Bond Formation with Tridentate Nacnac Based Pyridine-imine Ligands and Study of a Tetradentate Diimine Redox Non-innocent Ligand
| Author | : Wesley Daniel Morris |
| Publisher | : |
| Total Pages | : 151 |
| Release | : 2014 |
| Genre | : |
| ISBN | : |
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First row transition metals are attractive candidates for catalysis because they are much more abundant, cheaper, and less toxic than their 2nd and 3rd row congeners. Unfortunately, these first row metals typically promote one electron (radical) processes instead of the two electron transformations observed in oxidation/reduction and bond breaking/forming reactions. One way around this is to use redox noninnocent ligands that have the capacity to store electrons and then release them over the course of the catalytic cycle to limit the oxidation state changes that occur at the metal center. The goal of this work was to expand the scope of redox non-innocent ligands in development of new catalytic processes. A tridentate ligand was synthesized that contained a 2-pyridine methylamine arm on a nacnac ligand backbone. Deprotonation at the methylene position formed a new redox non-innocent ligand that was stable only in the bis-reduced form chelated to Fe(II). The neutral ligand was prone to intramolecular cyclization via C-N bond formation to form a new pyrimidine ring structure while the monoanionic ligand was prone to reductive coupling with formation of a new carbon-carbon bond. This system showed a strong preference for maintaining a ferrous state of iron with C-C or C-N bond formation observed when the redox noninnocent ligand was in its neutral or mono-anionic form. A tetradentate ligand was synthesized with diimine and orthophenylenediamine functionalities that could exist in 5 different oxidation states from neutral to tetraanionic, which should support group transfer reactivity. The ligand was installed on iron and manganese to form standard M+2 coordination compounds. The corresponding chromium compound showed a different electronic structure consistent with a reduced ligand. Remarkably, it was shown calculationally to have an S=1 ligand antiferromagnetically coupled to a high spin Cr2+ metal center. Cyclic voltammetric measurements exhibited two reversible one-electron ligand reductions as well as three quasi-reversible oxidations consistent with 1 metal based oxidation and two ligand based oxidations.
