Electrochemistry, Chemical Reactivity, and Time-Resolved Infrared Spectroscopy of Donor-Acceptor Systems (Q(x))Pt(pap(y))) (Q = Substituted o-Quinone or o-Iminoquinone; pap = Phenylazopyridine)

摘要

The donor−acceptor complex [(O,NQ2−)Pt-ud(pap0)] (1; pap = phenylazopyridine, O,NQ0 = 4,6-di-tertbutyl-udN-phenyl-o-iminobenzoquinone), which displays strongudπ-bonding interactions and shows strong absorption in theudnear-IR region, has been investigated with respect to its redoxinducedudreactivity and electrochemical and excited-stateudproperties. The one-electron-oxidized product [(O,NQ•−)Pt-ud(pap0)](BF4) ([1]BF4) was chemically isolated. Single-crystaludX-ray diffraction studies establish the iminosemiquinone formudof O,NQ in [1]+. Simulation of the cyclic voltammograms of 1udrecorded in the presence of PPh3 elucidates the mechanismudand delivers relevant thermodynamic and kinetic parametersudfor the redox-induced reaction with PPh3. The thermodynamicallyudstable product of this reaction, complex [(O,NQ•−)udPt(PPh3)2](PF6) ([2]PF6), was isolated and characterized by X-ray crystallography, electrochemistry, and electron paramagneticudresonance spectroscopy. Picosecond time-resolved infrared spectroscopic studies on complex 1b (one of the positional isomersudof 1) and its analogue [(O,OQ2−)Pt(pap0)] (3; O,OQ = 3,5-di-tert-butyl-o-benzoquinone) provided insight into the excited-stateuddynamics and revealed that the nature of the lowest excited state in the amidophenolate complex 1b is primarily diimine-ligandbased,udwhile it is predominantly an interligand charge-transfer state in the case of 3. Density functional theory calculations onud[1]n+ provided further insight into the nature of the frontier orbitals of various redox forms and vibrational mode assignments.udWe discuss the mechanistic details of the newly established redox-induced reactivity of 1 with electron donors and propose audmechanism for this process.