Comparison of Electrochemically and Photochemically Induced Electron-Transfer Processes of a Series of Copper(II) Schiff Base Complexes with Thiolate Coordination

Abstract

The electrochemical and photoredox properties of copper(II) thiopyrazolone Schiff base complexes 1–9 with imine and thiolate coordination, showing variable degrees of tetrahedral distortion, were investigated by means of combined electrochemical and spectroscopic techniques in the temperature range of 193–293 K. The cyclic voltammograms of 1–9 in butyronitrile revealed that the reduction and oxidation paths are strongly dependent on the geometry of the CuN2S2 moiety. Due to the strong delocalization of the singly occupied redox orbital (SOMO) the oxidations and reductions occur in a narrow potential range. The one‐electron‐reduced 1(r)–9(r) and oxidized 1(o)–9(o) products were electrogenerated and stabilized inside optically transparent thin‐layer electrochemical (OTTLE) cells at variable temperatures and could be characterized for the first time by UV/Vis spectroscopy. The reduced formal d10 copper(I) species absorb only weakly in the visible region. The oxidized products 1(o)–9(o) show several strong absorptions in the visible region due to the presence of formal d8 copper(III) species. The spectral information allowed assignment of the initial photoproducts. Irradiations in donor media such as THF or EtOH initially produces 1(r)–9(r). No photoreduction was observed in tBuOH which cannot liberate reducing Hα. The primary oxidized species 1(o)–9(o) were formed in chlorinated acceptor solvents (CHCl3) on UV irradation. Fast relaxation to the ground state prevents the photoredox reactions from CT or LF excited states.

Adamantane-like Cluster Complexes of Mixed-Valent Copper−Copper and Nickel−Copper Thiolates

“…The cyclic voltammogram, shown in Figure a, of (bme*daco)Cu in acetonitrile solution shows one reversible reduction wave centered at −1.07 V vs NHE, a quasireversible oxidation wave at +0.01 V, and a second irreversible oxidation event at ca. +0.55 V. The event at −1.07 V is assigned to the Cu II/I couple and is considerably more negative than that in monomeric N 2 S 2 Cu II complexes where there is a ligand-imposed tetrahedral twist that better accommodates the reduced Cu I d 10 species . For example, the reversible Cu II/I redox couple of the Schugar N 2 S 2 Cu II complex, structure C , is −0.51 V vs NHE, measured in acetonitrile and referenced to Fc/Fc + .…”

π-Complexes of Tropolone and Its N-Derivatives: Ambidentate [O,O]/[N,O]/[N,N]-Cycloheptatrienyl Pentamethylcyclopentadienyl Ruthenium Sandwich Complexes

“…Peak potential splittings are 440 mV ( 14 ) or 220 mV ( 15 ) at a sweep rate of 25 mV/s and steadily increase along with severe damping of the anodic reverse peak as the sweep rate is increased. Such behavior is characteristic of Cu(II)/Cu(I) redox couples that are usually accompanied by structural rearrangements as the coordination geometry at the metal changes from square planar to tetrahedral. − Complex 14 , with its κ 2 -[O,O] ligands, displays another irreversible reduction close to the electrolyte discharge limit, which is shifted outside the accessible potential window for complex 15 . Cyclic voltammograms of 14 and 15 also show an additional oxidation, whose peak current is very similar to that for the first reduction wave and is thus also assigned as a one-electron process.…”

{Dimethyl [2,2′-(ethane-1,2-diyldioxy)bis(benzylidenehydrazono)]bis(dithioformato)-κ4S,N,N′,S′}copper(II)

“…For related literature, see: Balamurugan et al (2004); Knoblauch et al (1999); Solomon et al (1992).…”

“…Investigations of the coordination chemistry of [CuN 2 S 2 ] complexes revolve around the development of mimics for blue copper centers (Balamurugan et al, 2004). Few [CuN 2 S 2 ] complexes and their crystal structures have been reported (Knoblauch et al,1999). In (I), the ethane-1,2-bis( (2 and their proximity distorts the geometry.…”