Main Group and Transition Metal Complexes: From Fundamental Investigations to Photocatalysis

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This proposal addresses fundamental and applied aspects of compound design and catalyst development. More specifically, the proposal presents three core research themes: an exploration of noncovalent bonding interactions to metal centers; strategies to control anisotropy of single metal ions in complexes; and enhancing the light harvesting ability of Re compounds with the target of improved photocatalytic reduction of CO2. The first theme is centered on the fundamental objective to design and assemble molecular scaffolds that display an unusually low degree of covalent bonding between a metal cation and an associated Lewis base. Such noncovalent interactions is an important across diverse fields of molecular, biological and polymer science. We are contributing to a completely unique aspect of noncovalent interactions to inorganic chemistry. Prior to our work, the fundamental questions on how to control metal ligand bonding were not explicitly appreciated. The impact of these important fundamental interactions in main group chemistry has recently been appreciated in the literature to which we contributors. Understanding how to control metal-ligand bonding provides insights into methods to influence the Lewis acidity of metal cations, which directs aspects of their chemistry, and challenges conventional bonding descriptions of metal-ligand interactions. Our strategy is based on selecting bonding groups with restricted geometric features that dictate the alignment of their bonding features. We further extend this work to include main group compounds that are able to activate a number of small molecules (e.g. CO2, carbonyls, alkynes and nitrile bonds). This reactivity will be an important step forward in the realization of main group catalyst development. The fundamental motivation of our second theme is to control and dictate the electronic anisotropy of transition metal and f-element ions. Through steric and electronic tuning we will engender changes in physical, chemical, and magnetic properties of complexes. One objective is to produce single-ion cobalt and iron complexes whose anisotropies will reveal themselves as individual molecular magnets (so-called “single-molecule magnets”). Our approach provides us the unique opportunity to address the prediction of magnetic anisotropy based and thus remove some of the serendipity that is normally used in the synthetic work on SMMs. We also anticipate that this will lead to design of molecular magnetic building blocks. The control of geometric and electronic structure applied to catalysis are the concepts behind our third core theme which provides a major change to the photochemical and photophysical properties and applications of Re(I) complexes. While these features have been recognized since for some time and are noteworthy for the exceptional ability of these compounds to photocatalytically reduce CO2, the development of this field has been restricted by the limited structural and electronic variability of the common pseudo-octahedral fac-[ReX(CO)3L2] compounds. We will addresses these constraints by developing a new compounds that possess new coordination geometries for the Re centers. This new structure significantly elaboration of the basic photophysical features of this large class of compounds and should yield improved catalysts that would function with lower energy. Longer range objectives are targeting new approaches at Re(I) multimetallic networks. We also plan to expand this chemistry to novel porous materials that can function as heterogeneous CO2 ¬reduction catalysts as well as a means to study the changes to the fundamental changes to the photophysical features of the Re centers when arranged in ordered arrays.