ELECTRON-TRANSFER KINETICS OF COPPER(II I) COMPLEXES WITH DIALCOHOLICDERIVATIVES OF THE MACROCYCLIC TETRATHIAETHER[14]ANES4 - EFFECT OF SIMPLE RING SUBSTITUENTS UPON GATED BEHAVIOR/

Studies have been conducted on the electron-transfer kinetics of the C u(II/I) complexes formed with two dialcoholic derivatives of the macro cyclic tetrathiaether [14]aneS4, syn- and anti-3,6,10,13-tetrathiacycl otetradecane-1,8-diol. For Cu(II/I)(syn-[14]aneS4-diol), the self-exch ange rate constant has been determined directly from NMR line broadeni ng: k11(ex) = 2.9 X 10(3) M-1 S-1 (25-degrees-C), DELTAH(double dagger ) = 33 +/- 5 kJ mol-1, DELTAS(double dagger) = -68 +/- 20 J K-1 mol-1. For both Cu(II/I)L systems, extensive cross-reaction electron-transfe r kinetics have also been measured using four different reductants and four different oxidants, spanning a wide range of reaction potentials . The patterns in the k11 values obtained by application of the Marcus square root relationship are consistent with the previously proposed dual-pathway square scheme mechanism in which both pathways have been accessed. Under appropriate conditions, limiting first-order kinetics, independent of the counter reagent concentration, have also been obse rved for the oxidation of both Cu(I)L species, indicating the onset of conformationally-controlled ''gated'' behavior. The evaluated self-ex change rate constants representative of each pathway (i.e., k11(A) and k11(B) in units of M-1 s-1) and the evaluated rate constant for the C u(I)L conformational change (k(RP) in units of s-1) are as follows at 25-degrees-C and mu = 0.1 M: for the syn complex, log k11(A) = 3.6 +/- 0.2, log k11(B) = -0.4 +/-0.3, and log k(RP) = 2.20 +/- 0.02; for the anti complex, log k11(A) = 4.3 +/- 0.2, log k11(B) = -2.0 +/- 0.4, an d log k(RP) = 1.70 +/- 0.03. The 10(6)-fold difference in the k11 valu es obtained for the two pathways in the latter system represents the w idest range of conditions for gated behavior yet observed, suggesting that the Cu(II)L metastable intermediate (Q) is particularly unstable relative to the Cu(I)L metastable intermediate (P). Crystallographic s tructural data are also reported for each of the Cu(II)L species. [Cu( II)(syn-[14]aneS4-diol)(ONO2)]NO3 crystallizes in the monoclinic space group P2(1)/a with a = 9.238(1) angstrom, b = 13.248(2) angstrom, c = 15.321(2) angstrom, beta = 104.21(1)degrees, V = 1817.5(4) angstrom3, Z = 4; [Cu(II)(anti-[14]aneS4-diol)](ClO4)2 crystallizes in the moncl inic space group P2(1)/c with a = 5.8472(9) angstrom, b = 17.764(3) an gstrom, c = 9.601(1) angstrom, beta = 102.43(1)degrees, V = 973.8(2) a ngstrom3, Z = 2.