Date of Award
Fall 2025
Document Type
Open Access Dissertation
Department
Chemistry and Biochemistry
First Advisor
Richard D. Adams
Abstract
Zwitterionic onium ylides, such as [R3X+CH2-], where X = N, P, are useful reagents for chemists in a number of organic chemical reactions, including the synthesis of natural products and molecules with pharmacological and biological activity. However, many of the metal-free ylides are unstable.
The first chapter of this dissertation discusses zwitterions, both metal-free and metal-stabilized, their uses, and the ability of metal-complexed zwitterions to accelerate the production of new carbon-carbon bonds, so opening up a new route for organic synthesis.
In subsequent chapters, a comprehensive investigation of Me3NO-mediated transformation of rhenium and osmium carbonyl halides and aryls is reported, resulting in a novel family of zwitterionic ammonio-ethenyl and α-functionalized metal–carbonyl complexes. Using trimethylamine N-oxide to oxidatively decarbonylate BrRe(CO)5 and Br₂Os(CO)4 (and related cluster precursors) produces 16-electron M(CO)4 fragments. These fragments are then carefully captured by neutral donors (NMe3, ONMe3), alkynes (C2H2, ethoxyacetylene), and diazo precursors to produce substitution, vinylation, and carbene-capture products.
The neutral ReBr(CO)4(NMe3) (1), zwitterionic ReBr(CO)4[CH=CH(NMe3)] (2), and the α-ester alkyl ReBr(CO)4[HC(NMe3)CO2Et] (3) are important rhenium products. Analogous osmium mono- and multi-metal zwitterions (6–11) were made from Br2Os(CO)4 and Br2Os3(CO)12. RePh(CO)5 (5) and OsPh2(CO)4 (12), which are valuable precursors for comparable vinyl–NMe3 functionalization, are produced by aryl transfer from SnPh4.
In a complementary study, an unusual complex, W(CO)5(ONMe3) (19), was isolated in the reaction between W(CO)6 and NMe3O, and upon reaction with ethoxyacetylene, it was easily converted to W(CO)5[HC(NMe3)CO2Et] (20), demonstrating the dual oxidant/oxygen-donor behavior of Me3NO. IR, multinuclear NMR, mass spectrometry, and single-crystal X-ray diffraction were used to confirm the structures of representative products. Spectroscopic trends and crystallographic metrics support the assignment of pseudo-octahedral M(I/II) cores bearing distant quaternary ammonium substituents, formal negative metal centers, and strongly σ-donating vinyl/alkyl ligands.
The proposed mechanisms involve stepwise CO abstraction, alkyne coordination, and nucleophilic attack of neutral nucleophile (including, for diazo pathways, transient metal-carbene intermediates). These findings provide flexible, structurally defined building blocks for organometallic synthesis and possible catalytic or material applications, adding C–C and C–N bond formation at low-valent centers to the field of Me3NO chemistry.
Rights
© 2025, Matthew Olaide Ariwoola
Recommended Citation
Ariwoola, M. O.(2025). Studies of Zwitterionic Metal Complexes: Reactions of Alkynes with Metal Carbonyl Compounds and Neutral Nucleophiles. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/8650