Ylidic Substituents for Electron Rich Organic Materials with Synthetic and Energy Storage Applications

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Modification of the properties of a compound can be achieved by careful selection of the substituents, the groups attached to the parent structure. Among the multitude of substituents, amino groups, by virtue of their strong pi-donating properties, have been the most heavily used in applications where a more electron rich parent structure is required. We have recently demonstrated that, in contrast to the widespread belief that amino groups are the premier pi-donor substituent, iminophosphorano substituents (R3P=N-) are even stronger in this regard. We exploited this property to prepare the most powerful neutral organic electron donors, which act as homogeneous reducing agents. In complementarity to metal-based reagents, such organic reducing agents hold the promise of allowing for alternate reaction pathways, more mild conditions, and less environmental load. Nevertheless, substrate scope is limited and the reducing strength of many metal reagents greatly surpasses what is possible with the best organic reductants. This proposal will extend our work by developing new iminophospohrano substituents, as well as other substituents (iminosulfurao, and methylenephosphorano) that should be superb pi-donors. Hammett constants for these substituents will be determined, allowing for them to be ranked according to their pi-donor properties. While this information will be of value to chemists of all disciplines, we will utilize the most strongly donating substituents in the development of the most powerful organic reducing agents. This should open the door to the reduction of increasingly challenging substrates using milder conditions. New synthetic processes will thus be developed. As a second aspect of this research program, the strongly reducing organic compounds that we have already prepared, and that we target here, will be investigated as anode materials in organic redox flow batteries. Such redox flow batteries are regarded as promising candidates for large scale energy storage, including the storage of renewable energy for integration with power grids. The investigation of organic materials as active species, rather than metal-based compounds, is a new avenue of research for this technology, but currently there is a lack of low potential materials. Our compounds, coupled with readily available organic cathode materials, will be tested in organic redox flow batteries with the goal of developing systems with increased cell voltages and energy densities.