Electron exchange kinetics in a tetrahedrally coordinated copper(II)/(I) couple

Abstract

The four-coordinate anion Cul(dpym), (Hdpym = 3,3',5,5'-tetramethyl-4.4'-dicarboethoxydipyrromethene) can be prepared in solution in acetone either by electrochemical reduction of the known tetrahedral complex CuH(dpym)? (E' = -290 mV vs. SCE) or by the quantitative reaction of 2Hdpym with Cu(CH,CN),+ in the absence of 0,. The latter reaction does not go to completion in solvents that bind relatively strongly to CU' or that are poor proton acceptors. Ligand exchange between cu'(dpym),-and excess Hdpym in acetone is "fast" in the 'H NMR timeframe, with k, = 1.4 x lo7 L mol-' s-' at 298 K (first order in each reactant), AH^; = 3.4 2 0.6 kJ mol-', and AS,: = -97 ? 3 J K-I mol-'. In the absence of excess Hdpym, dissociation of Cu'(dpym); in acetone remains negligible. Homogeneous electron exchange between Cu1(dpym)< and ~u " ( d~y m )~ in acetone falls in the "slow" 'H NMR timeframe, with kc, = 5.9 x lo3 L mol-' s-I, AH,,$ = 48.5 2 3.0 kJ mol-I, and AS,,* = -10 2 I0 J K-' mol-', at ionic strength I = 0.007 mol L-' and 298 K, while for the same self-exchange on a Pt electrode the heterogeneous rate constant k,, = 0.16 ? 0.04 cm sf' at I = 0.1 mol L-' and 298 K, according to AC voltammetry. These values of kc, and kel are of the order expected for CU"" couples in which no significant change in coordination number or geometry accompanies electron transfer.Key words: Electron transfer, copper complexes, ligand substitution kinetics, dynamic NMR.RCsumCs : On peut prtparer l'anion tktracoordint Cul(dpym),-(Hdpym = 3,3',5,5'-tCtramCthy1-4,4'-dicarboCthoxydipyrromtthene) en solution dans l'acetone soit par une reduction Clectrochimique du complexe tetrakdrique ~u " ( d~~m )~ (EO = -290 mV vs. SCE) ou par la reaction quantitative de 2Hdpym avec le Cu(CH3CN),+ en l'absence de 0,. La dernikre reaction n'est pas complkte dans des solvants qui se lient relativement fortement au CU' ou qui sont de pauvres accepteurs de proton. L'Cchange de coordinat entre le Cul(dpym); et un excks de Hdpym dans l'acetone est rapide par rapport a la RMN du 'H; k, = 1,4 x lo7 L mol-' s-I t i 298 K (premier ordre par rapport B chaque reactif), AH,* = 3. [Traduit par le redaction] couples will tend to be rather slow if the normally preferred According to the Vallee-Williams principle (I), the rates of outer-sphere electron transfer processes involving copper(1ID)

An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

“…Takagi and Swaddle have been studying Cu(II/I) electron-exchange couples by NMR where the coordination geometries of Cu(I) and Cu(II) are constrained to be similar, the kinetic behavior is expected to follow the context of the moderately fast electron-transfer case, and no significant change in coordination number or coordination geometry was expected prior to the electron-transfer processes. 27,28 The gated electron-transfer process has been successfully interpreted by the square scheme, postulated by Rorabacher et al, as shown in Scheme 1. The theoretical studies of the gated electron transfer have been reported.…”

“…The estimated electron self-exchange rate constant of Cu(bid) 2 2+/+ is 0.16 kg mol -1 s -1 . Takagi and Swaddle have been studying Cu(II/I) electron-exchange couples by NMR where the coordination geometries of Cu(I) and Cu(II) are constrained to be similar, the kinetic behavior is expected to follow the context of the moderately fast electron-transfer case, and no significant change in coordination number or coordination geometry was expected prior to the electron-transfer processes. , …”

Redox Active DipyrrometheneCu(II) Monolayer for Oriented Immobilization of His‐Tagged RAGE Domains – the Base of Electrochemical Biosensor for Determination of Aβ16–23′

“…The complex dipyrromethene-Cu(II)-His 6 was described as distorted square-planar type [23][24][25][26].…”

Product of a DMF Aminalization, Bis[bis(3,5-dimethylpyrazol-1-yl)(dimethylamino)methane]copper(II) Perchlorate−Bis(dichloromethane)

“…These geometries have smaller ligand-field stabilization energies than the commonly observed tetragonal or square-planar coordination geometries. Pseudotetrahedral Cu(II)N 4 complexes have been prepared using geometrically constraining ligands such as 4 , 5 , and 6 . The tridentate ligand tris(3,5-diisopropylpyrazolyl)borate, 7 , has recently been used to construct pseudo-C 3 v CuN 3 S analogues of the type I copper metalloenzymes .…”