Browsing by Author "Irving, Charles D."

Now showing 1 - 4 of 4
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    Amide Synthesis through the In Situ Generation of Chloro- and Imido-Phosphonium Salts
    (ACS, 2020-06) Irving, Charles D.; Floreancig, Jack T.; Laulhé, Sébastien; Chemistry and Chemical Biology, School of Science
    We describe a methodology for the amidation of carboxylic acids by generating phosphonium salts in situ from N-chlorophthalimide and triphenylphosphine. Aliphatic, benzylic, and aromatic carboxylic acids can be transformed into their amide counter parts using primary and secondary amines. This functional group interconversion is achieved at room temperature in good to excellent yields. Mechanistic work shows the in situ formation of chloro- and imido-phosphonium salts that react as activating agents for carboxylic acids and generate an acyloxy-phosphonium species.
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    Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors
    (ACS, 2015-01) Dolai, Sukanta; Dutta, Poulami; Muhoberac, Barry B.; Irving, Charles D.; Sardar, Rajesh; Department of Chemistry & Chemical Biology, IU School of Science
    We have designed a new nonphosphinated reaction pathway, which includes synthesis of a new, highly reactive Se-bridged organic species (chalcogenide precursor), to produce bright white light-emitting ultrasmall CdSe nanocrystals of high quality under mild reaction conditions. The detailed characterization of structural properties of the selenium precursor through combined 77Se NMR and laser desorption ionization–mass spectrometry (LDI-MS) provided valuable insights into Se release and delineated the nanocrystal formation mechanism at the molecular level. The 1H NMR study showed that the rate of disappearance of Se precursor maintained a single-exponential decay with a rate constant of 2.3 × 10–4 s–1 at room temperature. Furthermore, the combination of LDI-MS and optical spectroscopy was used for the first time to deconvolute the formation mechanism of our bright white light-emitting nanocrystals, which demonstrated initial formation of a smaller key nanocrystal intermediate (CdSe)19. Application of thermal driving force for destabilization resulted in (CdSe)n nanocrystal generation with n = 29–36 through continuous dissolution and addition of monomer onto existing nanocrystals while maintaining a living-polymerization type growth mode. Importantly, our ultrasmall CdSe nanocrystals displayed an unprecedentedly large fluorescence quantum yield of ∼27% for this size regime (<2.0 nm diameter). These mixed oleylamine and cadmium benzoate ligand-coated CdSe nanocrystals showed a fluorescence lifetime of ∼90 ns, a significantly large value for such small nanocrystals, which was due to delocalization of the exciton wave function into the ligand monolayer. We believe our findings will be relevant to formation of other metal chalcogenide nanocrystals through expansion of the understanding and manipulation of surface ligand chemistry, which together will allow the preparation of “artificial solids” with high charge conductivity and mobility for advanced solid-state device applications.
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    Phosphonium-Salt Mediated Activation of C-O Bonds: Applications and Mechanistic Studies
    (2023-05) Irving, Charles D.; Laulhé, Sébastien; Manicke, Nicholas; Minto, Robert; Deng, Yongming
    The C-O single bond is found in numerous functional motifs including carboxylic acids, alcohols, and ethers. These compounds represent ideal precursors towards C-X (X = C, H, or heteroatom) bond formation due to their inherent stability and abundance in nature. As such, synthetic chemists continue to develop new technologies for the transformation of these precursors into biologically useful targets such as amides and amines. However, due to the stability of the C-O single bond, accessing such targets remains a consistent challenge. The activation of the carboxylic acids towards peptide synthesis has been facilitated through various coupling agents, including organoboron and transition metal catalysts. However, coupling agents can generate stochiometric, difficult-to-remove, toxic waste by-products. Organoboron/transition metal catalyzed condensations offer a more atom economical approach but suffer from varying degrees of optical erosion and poor sustainability. Phosphonium-based deoxyaminative technologies provide access to amines from alcohols via a phosphorus oxygen double bond formation driving force, but possesses a narrow nucleophilic nitrogen source scope, and poor atom economy. Transition metal/enzyme catalyzed “hydrogen borrowings” represent atom economical deoxyaminative alternatives. Still, their respective use of costly metals, and multiple enzymatic cascade steps severely limit the sustainability and scope of such protocols. An ambient deoxyamidation of carboxylic acids and deoxyamination of alcohols was developed through the use of N-haloimides activated by triphenylphosphine. Such technologies were found to possess broad functional tolerance and formed C-N bonds via a coupling to free amines, and the direct installment of the imide motif. Mechanistic experiments suggest that such transformations take place via the in situ generation of two separate phosphonium reactive species.
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    Synthesis of Imide and Amine Derivatives via Deoxyamination of Alcohols Using N-Haloimides and Triphenylphosphine
    (Wiley, 2021) Irving, Charles D.; Floreancig, Jack T.; Gasonoo, Makafui; Kelley, Alexandra S.; Laulhé, Sébastien; Chemistry and Chemical Biology, School of Science
    A deoxyamination methodology of activated and unactivated alcohols is presented. The reaction is mediated by phosphonium intermediates generated in situ from N-haloimides and triphenylphosphine. The protocol allows for the synthesis of phthalimide and amine derivatives in moderate to good yields at room temperature. A series of NMR experiments have provided insight into the reactive intermediates involved and the mechanism of this deoxyamination reaction.