Electrochemistry, Chemical Reactivity, and Time-Resolved Infrared Spectroscopy of Donor–Acceptor Systems [(Q<sup><i>x</i></sup>)Pt(pap<sup><i>y</i></sup>)] (Q = Substituted <i>o</i>‑Quinone or <i>o</i>‑Iminoquinone; pap = Phenylazopyridine)


The donor–acceptor complex [(<sup>O,N</sup>Q<sup>2–</sup>)­Pt­(pap<sup>0</sup>)] (<b>1</b>; pap = phenylazopyridine, <sup>O,N</sup>Q<sup>0</sup> = 4,6-di-<i>tert</i>-butyl-<i>N</i>-phenyl-<i>o</i>-iminobenzoquinone), which displays strong π-bonding interactions and shows strong absorption in the near-IR region, has been investigated with respect to its redox-induced reactivity and electrochemical and excited-state properties. The one-electron-oxidized product [(<sup>O,N</sup>Q<sup>•–</sup>)­Pt­(pap<sup>0</sup>)]­(BF<sub>4</sub>) ([<b>1</b>]­BF<sub>4</sub>) was chemically isolated. Single-crystal X-ray diffraction studies establish the iminosemiquinone form of <sup>O,N</sup>Q in [<b>1</b>]<sup>+</sup>. Simulation of the cyclic voltammograms of <b>1</b> recorded in the presence of PPh<sub>3</sub> elucidates the mechanism and delivers relevant thermodynamic and kinetic parameters for the redox-induced reaction with PPh<sub>3</sub>. The thermodynamically stable product of this reaction, complex [(<sup>O,N</sup>Q<sup>•–</sup>) Pt­(PPh<sub>3</sub>)<sub>2</sub>]­(PF<sub>6</sub>) ([<b>2</b>]­PF<sub>6</sub>), was isolated and characterized by X-ray crystallography, electrochemistry, and electron paramagnetic resonance spectroscopy. Picosecond time-resolved infrared spectroscopic studies on complex <b>1b</b> (one of the positional isomers of <b>1</b>) and its analogue [(<sup>O,O</sup>Q<sup>2–</sup>)­Pt­(pap<sup>0</sup>)] (<b>3</b>; <sup>O,O</sup>Q = 3,5-di-<i>tert</i>-butyl-<i>o</i>-benzoquinone) provided insight into the excited-state dynamics and revealed that the nature of the lowest excited state in the amidophenolate complex <b>1b</b> is primarily diimine-ligand-based, while it is predominantly an interligand charge-transfer state in the case of <b>3</b>. Density functional theory calculations on [<b>1</b>]<sup><i>n</i>+</sup> provided further insight into the nature of the frontier orbitals of various redox forms and vibrational mode assignments. We discuss the mechanistic details of the newly established redox-induced reactivity of <b>1</b> with electron donors and propose a mechanism for this process

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oai:figshare.com:article/2027853Last time updated on 2/12/2018

This paper was published in FigShare.

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