Date of Award
Spring 2015
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Chemistry
First Advisor
Gardinier, James R.
Second Advisor
Yi, Chae S.
Third Advisor
Fiedler, Adam
Abstract
There is currently a lot of interest in developing electrically conducting or semiconducting metal-organic frameworks (MOF's), highly porous materials constructed by organic ligands bridging metal centers. Typically MOF's are non-conducting and, moreover, they are susceptible to hydrolytic degradation. If hydrolytically stable and electrically conducting MOFs could be realized, then revolutionary new technologies could be envisioned. Currently, organic dicarboxylates are used as bridging organic ligands and one simple strategy to obtain the desired materials is to explore other ligand systems. Pincer ligands are organic compounds that are uninegative and bind metals in a tridentate, meridional fashion with two five-member chelate rings. There is intense contemporary interest in studying metal complexes of these pincer- or pincer-type ligands (variants with six-membered chelate rings) because they can exhibit remarkable stability and they can often promote unusual chemical transformations depending on the metal and any special properties of the ligand. Another attractive feature of pincer ligands for the purpose of developing conducting MOF's is that certain classes are electrochemically non-innocent, and can readily accept or give away electrons at potentials that depend on the ligand's constituents. This thesis describes investigations into metal complexes of new ligands that have either two pyrazolyl (pz) or one pz and one diphenylphospine flanking donor(s) attached to diarylamido anchor donors to give pincer-type derivatives with NNN- or NNP- donor sets, respectively. First, the preparation and reaction chemistry of (NNP)rhodium(I) complexes was investigated to determine their potential in catalytic chemistry. It was found by X-ray structural studies, NMR spectroscopic studies and DFT calculations that this ligand was hemilabile with rapid dissociation/association of the pyrazolyl arm. Next, the preparation and properties of [Ga(NNN)2](PF6) were thoroughly investigated experimentally and computationally. The complexes are hydrolytically stable. Moreover, electrochemical measurements show that the ligand is an electron donor, undergoing two sequential one-electron oxidations at potentials near 1.0 V vs Ag/AgCl. Spectroscopic studies verified that electronic communication occurs across a diamagnetic metal bridge and that the mono-oxidized species is a Robin-Day class IIA species. These results demonstrate that metal pincer complexes warrant further investigation as candidates for components of electrically conducting MOFs.