Redox reactivity of azathiaferrocenophane complexes with copper(II) and palladium(II)

Abstract

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(CH 3CN)(BF 4) 3, [ 1]Pd(PPh 3) 2(BF 4) 2 · CH 2Cl 2, [ 1]Pd(AsPh 3) 2 (BF 4) 2 · 1.5CH 2Cl 2, [ 1]Pd(C 6O 4Cl 2) · (HN(C 2H 5) 3) 2(BF 4) 2 · H 2O and [ 1]H 2Pd(bpy)(BF 4) 4. Copper(II) compounds reported include [ 2]Cu(CH 3CO 2) 2 · 2H 2O ( 2 = 1,5-bis(ferrocenyl)-3-thia-1,5-diaminopentane), [ 3]Cu(CH 3CO 2) 2 ( 3 = 1,8-bis(ferrocenyl)-3,6-dithia-1,8 -diaminooctane) and Cu(bas)(CH 3CO 2) 2 (bas = 3-thia-1,5-diaminopentane). The [ 1]HPd(CH 3CN) 3+ ca tion ( E 1 2 (F by tridentate S 2N ferrocenophane ligation, leaving one coordination position open to the CH 3CN 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(C 6O 4Cl 2) · (HN(C 2H 5) 3) 2(BF 4) 2 · H 2O is too weak to disrupt ferrocenophane tridentate chelation or to restore the Fe IIS bonding previously documented for [ 1]Pd(C 6O 4Cl 2), which was prepared by another synthetic route. Electronic spectra of [ 2]Cu(CH 3CO 2) 2 · 2H 2O and [ 3 ]Cu(CH 3CO 2) 2 are consistent with tridentate S 2N and tetradentate S 2N 2 ligat ion 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 Fell III/II couple. Although cyclic voltammetric waves for the Cu II,I couple were not observed, the redox reactivity of [ 2]Cu 2+ towards reduction was evaluated through a kinetic study of electron transfer within its mercaptoacetate adduct.