Structures and Reactions of Diplatinum Complexes

Citation

Darnton, Tania Victoria (2017) Structures and Reactions of Diplatinum Complexes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9NK3C2J. https://resolver.caltech.edu/CaltechTHESIS:04172017-185314743

Abstract

A d8−d8 complex [Pt₂(μ-P₂O₅(BF₂)₄]⁴⁻ (abbreviated Pt(pop-BF₂)⁴⁻) undergoes two 1e⁻ reductions at E_1/2 = −1.68 and E_p = −2.46 V (vs Fc⁺/Fc) producing reduced Pt(pop-B₂)⁵⁻ and superreduced Pt(pop-BF₂)⁶⁻ species, respectively. The EPR spectrum of Pt(pop-BF₂)⁵⁻ and UV−vis spectra of both the reduced and the superreduced complexes, together with TD-DFT calculations, reveal successive filling of the 6pσ orbital accompanied by gradual strengthening of Pt−Pt bonding interactions and, because of 6pσ delocalization, of Pt−P bonds in the course of the two reductions. Both reduction steps proceed without changing either d⁸ Pt electronic configuration, making the superreduced Pt(pop-BF₂)⁶⁻ a very rare 6p² σ-bonded binuclear complex. However, the Pt−Pt σ bonding interaction is limited by the relatively long bridging-ligand-imposed Pt−Pt distance accompanied by repulsive electronic congestion. Pt(pop-BF₂)⁴⁻ is predicted to be a very strong photooxidant (potentials of +1.57 and +0.86 V are estimated for the singlet and triplet dσ*pσ excited states, respectively).

Further study of the electronic excited states of Pt(pop-BF₂)^4- in the presence of luminescence quenchers revealed Stern-Volmer type dynamic quenching of the triplet state by trialkyl and triaryl amines. Quenching of the singlet as well as the triplet was observed in the presence of Co^II trisbipyridine complexes, but sample decomposition and the observed presence of simultaneous static and dynamic quenching behaviors hampered quantitative analysis.

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