Electron-Transfer Kinetics of Copper(II/I) Complexes with Dialcoholic Derivatives of the Macrocyclic Tetrathiaether [14]aneS4. Effect of Simple Ring Substituents upon Gated Behavior

Electron Transfer by Copper Centers

“…49,50 More extensive kinetic measurements were subsequently conducted on the 13-, 14-, and 15-membered ring tetrathiaethers and two dialcohol derivatives of [14]aneS 4 . 56,133,134 The electron-transfer kinetics for each of these five systems were measured with a total of four reductants and four oxidants, and independent k 11 values were also obtained from NMR line broadening measurements. 56,133,134 In all five systems, the calculated k 11(Red) values were in close agreement with the corresponding values obtained by NMR (Table 7).…”

“…56,133,134 The electron-transfer kinetics for each of these five systems were measured with a total of four reductants and four oxidants, and independent k 11 values were also obtained from NMR line broadening measurements. 56,133,134 In all five systems, the calculated k 11(Red) values were in close agreement with the corresponding values obtained by NMR (Table 7). This observation was in sharp contrast to the original suggestion by Lee and Anson 39 that the k 11 value for Cu(II/I) systems, as determined directly without invoking eq 14, should be the geometric mean of k 11(Red) and k 11(Ox) (see section 4.3).…”

“…Of the five Cu(II/I) complex systems noted above, k RP values of 50, 120, and 50 s -1 were reported for [14]aneS 4 , syn- [14]aneS 4 -diol, and anti- [14]aneS 4 -diol, respectively, with limiting values of g200 and e5 s -1 for the complexes with [13]aneS 4 and [15]aneS 4 , respectively. 56,133,134 If all three terms in eq 20′′ contribute to the reaction kinetics (i.e., second-order kinetics via pathway A, first-order kinetics due to rate-limiting conformational change, and second-order kinetics via pathway B) as the counterreagent concentration is varied, curve fitting can be used to resolve the individual values of k 21(A) , k 21(B) , and k RP . 134 A prime example of such multifold behavior is illustrated in Figure 15 for the oxidation of Cu I (trans-cypt- [14]aneS 4 ) + by Ni III ( [14]aneN 4 ) 3+ for which the three limiting conditions overlap significantly as the oxidant concentration is varied.…”

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

“…3 The electron-transfer regulated by the slowness of the change in coordination geometry has been reported for some copper(II/ I) couples with tetrathiamacrocyclic ligands. [4][5][6][7][8] Rorabacher et al precisely explored such "gated behavior" caused by sluggishness in the geometric interconversion and discovered that the oxidation of tetrahedral Cu(I) to tetragonal Cu(II) is slow in most cases when macrocyclic thioether ligands were used. In such cases, the electron exchange rate constant estimated by the application of the Marcus cross relation to the oxidation reaction of Cu(I) was not consistent with the directly measured electron exchange rate constant by using NMR.…”

Oxidatively Induced Isomerization of Square-Planar [Ni(1,4,8,11-tetraazacyclotetradecane)](ClO4)2

“…12,13 Both models have inspired much recent experimental work on Cu(II/I) systems by Kano et al 14 and especially by Rorabacher. [15][16][17][18][19] Unlike copper systems, relatively few investigations have addressed the effects that structural rearrangements have on redox processes of nickel complexes, [20][21][22][23] and presently no information is available for complexes possessing square-planar geometry. The present study represents the first detailed kinetic investigation of redox-induced structural rearrangement for a square-planar nickel center in aqueous media and provides insight into the sequential nature of the process.…”