UVM Theses and Dissertations
Format:
Print
Author:
Wu, Kan
Dept./Program:
Chemistry
Year:
2012
Degree:
PhD
Abstract:
M(CO)₃ (M = Mn, Re) complexes of three types of pseudo-cyclopentadienyl ligands have been characterized by electrochemical and spectroscopic methods. These Cp mimics are tris(pyrazolyl)borate anions (Tp and Tp*), tris(oxazolinyl)phenylborate anions (ToM and ToP) and a fullerene penta(organo)-adduct ([eta]⁵-C₆₀Me₅). Similar to the tris(pyrazolyl)borate ligands, the sterlc bulk imparted by the sp³-hybridized carbons in the oxazoline ring gives the tris(oxazolinyl)borate ligands significant structural protection against dimerization while leaving the M(CO)₃ face open for possible reactivity. The anodic electrochemistry of both scorpionate systems in relatively benign media (CH₂C1₂/[NBu₄4][B(C₆F₅)₄]) showed that their one-electron oxidation products were stable and persistent in the case of Re, but of limited stability in the case of Mn.
The E₁/₂ data were used to classify the electron-donating properties of the different scorpionate ligands in comparison with their cyclopentadienyl counterparts as Tp*> Cp*> ToP, Tp, ToM> Cp. Comparison of the Vco IR frequencies of these complexes gave a slightly different sequence of donor strength, Cp*, ToM, ToP> Tp*> Tp> Cp. The electronic effects of the tris(oxazolinyl)phenyl borate ligands are that they convey "Tp*-like" character in terms of the chemical reactivity, and "Tp-like" character in terms of the redox potentials of their complexes. The one-electron oxidation of the fullerene derivative was found to be mostly C₆₀-based.
Anodic oxidation reactions of half-sandwich tamoxifen (TAM) derivatives, M(CO)₃([eta]⁵-C₅H₄(Et)C=C(C₆H₄R)₂) (M = Mn, Re; R = H, OH, OMe) have been studied under nonaqueous conditions. These diarylethene complexes give radical cations which are charge-delocalized between the M(CO)₃ and TAM moieties. The Mn complexes undergo two one-electron oxidations that are largely reversible by cyclic voltammetry in CH₂C1₂/[NBu₄][B(C₆F₅)₄] media. However, the dications of the two Mn complexes having an oxygen-containing group in the para-phenyl position undergo chemical follow-up reactions.
Both the primary oxidation products and the long-term (electrolysis) products have been characterized by voltammetry and spectroscopy. Possible oxo-centered follow-up reactions leading to the formation of quinone methide species are proposed. The Re complex (R = H) is likely to undergo slow dimerization upon oxidations. The other Re complex (R = OMe) gives the two one-electron oxidations at about the same potential, resembling a single quasi-Nernstian two-electron process, and undergoes similar oxo-based follow-up reactions as the Mn complexes. The cation radical of the Mn complex (R = H) and the dication of the Re complex (R =OMe) undergo rapid substitution of one or more CO groups by phosphite ligands. Mn and Re complexes with finely tuned redox potentials can be obtained for cancer cell inhibition studies.
The E₁/₂ data were used to classify the electron-donating properties of the different scorpionate ligands in comparison with their cyclopentadienyl counterparts as Tp*> Cp*> ToP, Tp, ToM> Cp. Comparison of the Vco IR frequencies of these complexes gave a slightly different sequence of donor strength, Cp*, ToM, ToP> Tp*> Tp> Cp. The electronic effects of the tris(oxazolinyl)phenyl borate ligands are that they convey "Tp*-like" character in terms of the chemical reactivity, and "Tp-like" character in terms of the redox potentials of their complexes. The one-electron oxidation of the fullerene derivative was found to be mostly C₆₀-based.
Anodic oxidation reactions of half-sandwich tamoxifen (TAM) derivatives, M(CO)₃([eta]⁵-C₅H₄(Et)C=C(C₆H₄R)₂) (M = Mn, Re; R = H, OH, OMe) have been studied under nonaqueous conditions. These diarylethene complexes give radical cations which are charge-delocalized between the M(CO)₃ and TAM moieties. The Mn complexes undergo two one-electron oxidations that are largely reversible by cyclic voltammetry in CH₂C1₂/[NBu₄][B(C₆F₅)₄] media. However, the dications of the two Mn complexes having an oxygen-containing group in the para-phenyl position undergo chemical follow-up reactions.
Both the primary oxidation products and the long-term (electrolysis) products have been characterized by voltammetry and spectroscopy. Possible oxo-centered follow-up reactions leading to the formation of quinone methide species are proposed. The Re complex (R = H) is likely to undergo slow dimerization upon oxidations. The other Re complex (R = OMe) gives the two one-electron oxidations at about the same potential, resembling a single quasi-Nernstian two-electron process, and undergoes similar oxo-based follow-up reactions as the Mn complexes. The cation radical of the Mn complex (R = H) and the dication of the Re complex (R =OMe) undergo rapid substitution of one or more CO groups by phosphite ligands. Mn and Re complexes with finely tuned redox potentials can be obtained for cancer cell inhibition studies.