Polarity Inversion in Silicon and Phosphorus Compounds
The desire for new metal-free catalysts and reagents is currently fueling a renaissance in synthetic main group chemistry. The work herein describes efforts to design silicon and phosphorus compounds of inverse polarity with respect to conventional reactivity by accessing oxidation states that are a...
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| Format: | Thesis |
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Massachusetts Institute of Technology
2022
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| Online Access: | https://hdl.handle.net/1721.1/139046 https://orcid.org/0000-0001-6300-2570 |
| Summary: | The desire for new metal-free catalysts and reagents is currently fueling a renaissance in synthetic main group chemistry. The work herein describes efforts to design silicon and phosphorus compounds of inverse polarity with respect to conventional reactivity by accessing oxidation states that are atypical for these p-block elements. This umpolung approach affords novel reactivity that was previously unavailable to silicon and phosphorus molecules. In a first demonstration, synthetic and mechanistic studies of the 1,3-dipolar reaction of nitroarenes with geometrically constrained base-stabilized silylenes will be described. This cycloaddition initiates stepwise deoxygenation by silicon(II), and the application of this rare mode of reactivity to a room-temperature variant of the Cadogan reaction will be detailed. In a second section, tetragonal phosphorus(V) cations supported by a macrocyclic ligand exhibiting strong electrophilicity and hydrolytic stability will be disclosed. By virtue of the low-lying acceptor orbital enforced by the square pyramidal structure, these compounds are potent (yet water-tolerant) Lewis acids that catalyze carbonyl activation, C–H functionalization, and glucose deoxygenation. Finally, a combined experimental and theoretical study on a class of geometrically constrained phosphine imides (i.e., phosphazenes) will be discussed. By imposition of non-VSEPR geometries through cyclic constraint, these vicinal ambiphilic P(V) compounds readily undergo unorthodox 1,2-addition reactions as a function of increased electrophilic character at the nominally inert phosphorus center. Taken together, the development of new Si- and P-based reaction chemistry showcases the many opportunities for discovery of useful methods enabled by innovations in p-block molecular design. |
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