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Evaluation of Axial Pt···N Interactions and their Influence on the Reactivity and Redox Properties of Platinum(II) Complexes with Pincer Ligands

Muvirimi, Ronnie
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378194658

Abstract Details

2013, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
A series of platinum(II) complexes with the formulae Pt(R2NCN)(tpy)+, (tpy=2,2′:6′,2″-terpyridine; R2NCN- =2,6-bis(cyclic amine-methyl)phenyl anion; R = cyclic amine = piperidyl (pip); morpholinyl (mor); methylpiperizinyl (mepiz); thiomorpholinyl (tmor); and methylpiperidinyl (mepip)) was prepared. The tpy ligand is tridentate, whereas the R2NCN- ligand is monodentate, bonded through the central aryl group with the cyclic amines dangling above and below the axial coordination sites. A series of experiments were undertaken in order to evaluate the influence of axial Pt···N axial interactions on the reactivity and redox properties. 195Pt NMR chemical shifts are very sensitive to variations in the basicity of the amine groups, providing strong evidence for the existence of non-covalent axial Pt··· interactions in solution. The axial Pt···N interaction were detected and assessed by measuring the barriers to inversion for the dangling cyclic amines. The difference between the barrier to inversion of the free ligand and complex was interpreted as a measure of the extent of interaction between the dangling amines and Pt metal center. Structural, spectroscopic and electrochemical results suggest that changes in the donor properties of the dangling nucleophiles has remarkable influence on the reactivity of the Pt(R2NCN)(tpy)+ complexes. The electrochemical properties of these complexes were characterized by a combination of cyclic voltammetry, bulk electrolysis and spectroelectrochemistry. Cyclic voltammetric measurements demonstrated that changing the donor properties of the dangling groups tunes the potential by ~100 mV. The scan rate dependence of cyclic voltammograms of Pt(R2NCN)(tpy)+ presented here are consistent with a stepwise electron-transfer in which the second electron transfer step is slightly more favorable than the first (i.e., E2°′>E1°′). The axial Pt···N interactions preorganizes the complex for electron transfer, thereby increasing the rate of heterogeneous electron transfer. The formal potentials for the Pt(IV)/Pt(III) (E1°′) and Pt(III)/Pt(II) (E2°′) one-electron reductions, the heterogeneous rate constants (ks1 and ks2) and transfer coefficients (a1 and a2) were determined from scan rate dependent cyclic voltammmetric data and optimized by digital simulation. In all cases, the results confirm that the E1°′ and E2°′ couples are inverted by several hundred millivolts indicating that a significant thermodynamic destabilization occurs upon the addition of the first electron during the anodic process. The slower electron-transfer rate for the Pt(III)/Pt(II) redox couple also indicates that the major structural reorganization occurs during the anodic addition of the first electron. The relationship between these assembled parameters, as well as the spectroscopic data, was discussed in context of Pt···N interactions. The [Pt(tpy)X3](PF6) (X= Cl-; or Br-) complexes undergo a metal centered irreversible reduction that is accompanied by loss of axial halide ligands. The interconversion of Pt(II) and Pt(IV) using electrochemical methods is chemically reversible, but completely electrochemically irreversible. Chemical oxidation of Pt(tpy)X3+ by electrochemically generated X2 and electrochemical reduction of Pt(tpy)X3+ results in remarkable hysteresis in the electrochemistry of the Pt terpyridyl halide complexes.
William Connick, Ph.D. (Committee Chair)
Michael Baldwin, Ph.D. (Committee Member)
James Mack, Ph.D. (Committee Member)
200 p.
Inorganic Chemistry
two-electron transfer; electrochemistry; terpyridine; platinum II; redox; pincer ligands

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Citations

  • Muvirimi, R. (2013). Evaluation of Axial Pt···N Interactions and their Influence on the Reactivity and Redox Properties of Platinum(II) Complexes with Pincer Ligands [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378194658

    APA Style (7th edition)

  • Muvirimi, Ronnie. Evaluation of Axial Pt···N Interactions and their Influence on the Reactivity and Redox Properties of Platinum(II) Complexes with Pincer Ligands. 2013. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378194658.

    MLA Style (8th edition)

  • Muvirimi, Ronnie. "Evaluation of Axial Pt···N Interactions and their Influence on the Reactivity and Redox Properties of Platinum(II) Complexes with Pincer Ligands." Doctoral dissertation, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1378194658

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.