The synthesis and application of highly reducing bispyridinylidene electron donors
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Date
2020
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University of New Brunswick
Abstract
The incorporation of iminophosphorano substituents (-N=PR[subscript 3]) onto the electron-rich bispyridinylidene (BPY) scaffold has allowed for the development of electron donors with exceptionally low redox potentials. By substitution of the –R group on phosphorus, various reductive strengths of the BPY can be achieved, allowing for enhanced selectivities. In order to expand the application of these reductants in organic synthesis, the range of redox potentials must be further developed, thereby increasing the need for stronger electron donors.
In recent years, a tetrasubstituted BPY was prepared utilizing four triphenyl- iminophosphorano groups (-N=PPh[subscript 3]), located ortho and para to the pyridyl nitrogen of the BPY scaffold. This resulted in the strongest organic electron donor to date, with a record-breaking redox potential of -1.70 V vs. SCE. The donor was probed for its reductive capabilities, establishing success in the ground-state reduction of various challenging substrates. Recently, a novel tetra(iminophosphorano)-substituted BPY of increased reductive strength has been prepared. This study will describe its utility in reducing similar challenging organic substrates, in efforts to provide milder reaction conditions, as well as increasing the substrate scope. In addition, the synthesis of a novel bis(iminophosphorano)-substituted BPY, derived from a highly electron-rich phosphine, was explored. This study will describe a proposed synthetic route toward its preparation, where its synthesis could assist in expanding the range of reduction potentials accessible by organic reductants.