Reactivity of the Acyclic Diazadioxa Redox Active Ligand [(C(5)H(5))Fe(C(5)H(4)CH(2)N(CH(3))(CH(2))(2)OCH(2)-)](2): NMR, Electrochemical, and Mössbauer Studies. Crystal Structure of Its Copper Complex.

Abstract

Several novel diazadioxa ferrocenyl derivatives have been prepared along with their previously unknown electroactive precursor [(C(5)H(5))Fe(C(5)H(4)CH(2)N(CH(3))(CH(2))(2)OCH(2)-)](2) (2). Di-N,N'-protonated and -methylated species [2(H)(2)][X](2) (3a-c) (X = CF(3)SO(3), BF(4), PF(6)) and [2(Me)(2)][CF(3)SO(3)](2) (5), and N-H-N monoprotonated species [2H][X] (4a-c) have been isolated in high yield. The efficient syntheses of compounds [2Na][PF(6)] (6), [2Cu][CF(3)SO(3)] (7), [2Ag][CF(3)SO(3)] (8), and [2MCl(2)] (M = Zn, Hg) (9, 10) are reported. The crystal structure of complex 7 has been determined by X-ray analysis at 180 K. Crystal data: monoclinic P2(1)/c, with a = 11.511(2) Å, b = 19.613(2) Å, c = 14.493(2) Å, beta = 88.32(2) degrees, V = 3273.2(1) Å(3), Z = 4; R = 0.034, R(w) = 0.039 for 3379 observations and 407 variable parameters. The copper(I) atom, bound to the two O and two N atoms of the ferrocenyl ligand, is in a very distorted tetrahedral geometry with a large N(1)CuN(2) angle (163.1(2) degrees ). In cyclic voltammetry, 4a-c undergo two quasi-reversible (Fe(II)/Fe(III)) redox processes at 0.1 V s(-)(1). Electrochemical studies of 3a-c, 5, 7, and 8 show that diprotonation and dialkylation of 2 or complexation of a Cu (Ag) salt induces an anodic shift ranging from 240 to 110 mV. Chemical oxidation of 2 (5 equiv of Ag(I)) produces the cation [2(H)(2)](4+) (11). The quantitative two-step electrochemical oxidation of 2 at controlled potential in CH(3)CN also leads to 11: an ECE mechanism, in which the diprotonated species plays a key role, is proposed. Mössbauer data of 2, 3c, 6, 7, 8, and 11 are also presented.