REDOX REACTIVITY OF AZATHIAFERROCENOPHANE COMPLEXES WITH COPPER(II) AND PALLADIUM(II)

To further probe the influence of coordinated metal ions on the electrochemical behavior of azathiaferrocenophane ligands, a series of palladium(II) and copper(II) complexes with both cyclic and acyclic ferrocenophanes has been prepared, spectroscopically characterized and examined by cyclic voltammetry. New complexes of N,N-didecyl-2,8-diaza-5-thia[9](1,1') ferrocenophane (1) are [1]HPd(CH3CN)(BF4)(3), [1]Pd(PPh(3))(2)(BF4)(2).CH2Cl2, [1]Pd(AsPh(3))(2)(BF4)(2).1.5CH(2)Cl(2), [1]Pd(C6O4Cl2). (HN(C2H5)(3))(2)(BF4)(2).H2O and [1]H2Pd(bpy)(BF4)(4). Copper(II) compounds reported include [2]Cu(CH3CO2)(2).2H(2)O (2 = 1,5-bis(ferrocenyl)-3-thia-1,5-diaminopentane), [3]Cu(CH3CO2)(2) (3 = 1,8-bis(ferrocenyl)-3,6-dithia-1,8-diaminooctane) and Cu(bas)(CH3CO2)(2) (bas = 3-thia-1,5-diaminopentane). The [1]HPd(CH3CN)(3+) cation (E(1/2)(Fe-III/(II) = 0.59 V versus NHE in CH2Cl2, 0.1 M TBAP, 25.0 degrees C) is characterized by tridentate S2N ferrocenophane ligation, leaving one coordination position open to the CH3CN ligand and a protonated aza nitrogen atom uncoordinated. In contrast, 1 ligates Pd-II only through its pair of thioether sulfur atoms in [1]Pd(PPh(3))(2)(2+) (E(1/2) = 0.58 V) and [1]Pd(AsPh(3))(2)(2+) (E(1/2) = 0.59 V). The Pd-II-chloranilate interaction in [1]Pd(C6O4Cl2).(HN(C2H5)(3))(2)(BF4)(2).H2O is too weak to disrupt ferrocenophane tridentate chelation or to restore the Fe-II-S bonding previously documented for [1]Pd(C6O4Cl2), which was prepared by another synthetic route. Electronic spectra of [2]Cu(CH3CO2)(2).2H(2)O and [3]Cu(CH3CO2)(2) are consistent with tridentate S2N and tetradentate S2N2 ligation of Cu-II, respectively, and a finding of E(1/2) = 0.48 V for both complexes is in accord with expectations for the electrostatic influence of a bivalent cation on the Fe-III/(II) couple. Although cyclic voltammetric waves for the Cu-II,Cu-I couple were not observed, the redox reactivity of [2]Cu2+ towards reduction was evaluated through a kinetic study of electron transfer within its mercaptoacetate adduct.