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Leobardo Rodriguez Segura dissertation (FINAL).pdf (9.12 MB)

Put A Ring On It: The Discovery And Investigation Of The Non-Innocence Of TIM In COIII(TIM) Complexes

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posted on 2024-04-12, 12:42 authored by Leobardo Rodriguez SeguraLeobardo Rodriguez Segura

The use of redox non-innocent ligands to imbue third-row transition metal complexes with properties emulating those of their fourth- and fifth-row congeners has become an attractive strategy to overcome the limited resources and environmental implications associated with the latter class of metals. The tetra-imine macrocycle, TIM (2,3,9,10-tetramethyl-1,4,8,11-tetraza-cyclotetradeca-1,3,8,10-tetraene), which bears two sets of potentially redox-active α-diimine units, therefore, has been targeted as the ligand scaffold to investigate the structural and electronic properties of various organocobalt(III) complexes within this work.

First, the reaction between trans-[Co(TIM)Cl2]+ and terminal alkynes (HC2Ar), in the presence of triethylamine, yielded a series of mono- and bis-alkynyl CoIII(TIM) complexes, as discussed in Chapters 1 and 2. Interestingly, the use of electron-rich terminal alkynes (HC2Y) favors the formation of products featuring a 1-aza-2-cobalt-cyclobutene unit. As detailed in Chapter 3, the trans-[Co(TIM')(HC=C)Y)Cl]+-type complexes (TIM' = the resulting derivative of TIM) were prepared through the addition of HC2Y to trans-[Co(TIM)Cl2]+ in the presence of KOH. The unprecedented involvement of the TIM ligand was verified crystallographically and through 1H NMR and FT-IR spectroscopies. In Chapter 4, the properties and influences of the aza-cobalt-cyclobutene are further explored through UV-vis spectroelectrochemical studies on the constitutional isomers, trans-[Co(TIM)(C2Fc)Cl]+ and trans-[Co(TIM')((HC=C)Fc)Cl]+ (Fc = ferrocene). Moreover, the reactivity of the CoIII center in the latter complexes is investigated via the reaction with KCN and AgOTf in CH3CN.

In Chapter 5, a new facet of CoIII(TIM) reactivity is revealed through the reaction between trans-[Co(TIM)Cl2]+ and HC2Ar, in the presence of NaBH4. The reaction generates both mono- and bis-alkenyl complexes along with products containing a 1-aza-2-cobalt-cyclopropane unit. The formation of the former class of products is postulated to proceed through a transient H-CoIII(TIM) intermediate, while the latter is believed to be accessed upon the reduction of an imine moiety within the TIM ligand. Moreover, the generation of the three-membered ring showcases another example of the non-innocent nature of the TIM ligand.

History

Degree Type

  • Doctor of Philosophy

Department

  • Chemistry

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Tong Ren

Additional Committee Member 2

Suzanne C. Doucette Bart

Additional Committee Member 3

Shelley A. Claridge

Additional Committee Member 4

Justin L. Andrews

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