Electron-Transfer Kinetics and Thermodynamic Characterization of Copper(II/I) Complexes with Acyclic Tetrathiaethers in Aqueous Solution.
The kinetics of a series of Cu(II/I)-acyclic tetrathiaether complexes reacting with several oxidizing and reducing reagents have been examined in aqueous solution at 25 degrees C. This investigation has included a re-examination of Cu(II/I)(Me(2)-2,3,2-S(4)) (Me(2)-2,3,2-S(4) = 2,5,9,12-tetrathiatridecane = L12a), containing the ethylene-trimethylene-ethylene bridging sequence, plus three newly synthesized ligands containing an alternate bridging sequence of trimethylene-ethylene-trimethylene: 2,6,9,13-tetrathiatetradecane (Me(2)-3,2,3-S(4) = L12b) and two cyclohexanediyl-substituted derivatives, viz., cis-1,2-bis[(3-methylthiopropyl)thio]cyclohexane (cis-cyhx-Me(2)-3,2,3-S(4) = L14) and trans-1,2-bis[(3-methylthiopropyl)thio]cyclohexane (trans-cyhx-Me(2)-3,2,3-S(4) = L15). The corresponding phenylene derivative, 1,2-bis[(3-(methylthio)propyl)thio]benzene (bz-Me(2)-3,2,3-S(4) = L13), was also synthesized but did not form a measurable copper complex. The conditional stability constants for Cu(II)L (K(Cu)()II(L)(')) and Cu(I)L (K(Cu)()I(L)(')) and the Cu(II/I)L formal redox potentials (E(f)) vs NHE at 25 degrees C (generally at &mgr; = 0.10 (NaClO(4))) are as follows: for L12b, 15 M(-)(1), 1.0 x 10(13) M(-)(1), 0.83 V; for L14, 2.8 x 10(2) M(-)(1), 0.9(5) x 10(13) M(-)(1), 0.75 V; for L15, 8.8 x 10(2) M(-)(1), 6.(3) x 10(13) M(-)(1), 0.77 V. Application of the Marcus relationship to the experimentally determined cross-reaction rate constants yielded self-exchange rate constants for all four Cu(II/I)L acyclic systems which were relatively constant for both oxidation and reduction under a wide range of conditions. This contrasts sharply with previous results obtained for corresponding macrocyclic ligand systems.
Dunn
Brian C.
BC
Departments of Chemistry, Wayne State University, Detroit, Michigan 48202, and University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54701.
Wijetunge
Prabodha
P
Vyvyan
James R.
JR
Howard
Turner A.
TA
Grall
Andrew J.
AJ
Ochrymowycz
L. A.
LA
Rorabacher
D. B.
DB