Redox- und Koordinationschemie von Bisguanidinderivaten desCatechols und o-Benzochinons

Abstract

In this thesis, the redox and coordination chemistry of bisguanidino-functionalized dioxolenes (GFD) is studied. These GFD are hybrid compounds consisting of guanidino-functionalized aromatics (GFA) and dioxolenes. In the oxygen-protected GFD form, electrochemical and chemical oxidation experiments show that the 4,5-bisguanidino-benzodioxoles 1Ac (tetramethylguanidino), 2Ac (N,N‘-dimethyl-N,N‘-ethylen-guanidino-) and 5,6-bisguanidino-benzodioxin 2Et (N,N‘-dimethyl-N,N‘-ethylen-guanidino-) can be oxidized reversibly in two 1e- redox processes. In the coordination and redox chemistry of the mononuclear Cu complexes, it is found that the electron donor strength of the protected GFD (L = 1Ac, 2Ac, 2Et) covers precisely the crucial range to study systematically which factors stabilize the electronic structures [L0(CuIIX2)] or [L+•(CuIX2)]. The electronic structure depends on the electron donor strength of the redox active bisguanidine (L = 1Ac, 2Ac, 2Et), the coligand X (X = OAc, Cl, Br), the solvent and the temperature. In the halide complexes [L(CuX2)] with L = 2Ac, 2Et, a temperature- and solvent-dependent equilibrium between the valence tautomers [L0(CuIIX2)] and [L+•(CuIX2)] is found in solution, which affect the redox chemistry of [L(CuX2)]. The influence of the intramolecular electron transfer (valence tautomerism between [(L)2CuII]2+ and [(L+•)CuI(L)]2+) on the intermolecular redox process [(L)2Cu]2+/+ is found in the bis-bidentate guanidine copper complexes and has been studied. Based on the distorted structure (between quadratic-planar and tetrahedral) and low calculated reorganization energy, the prerequisites for efficient intra- and intermolecular electron transfer are given. The coordination and redox chemistry of mononuclear cobalt complexes with the protected GFD reveals that [(L)2Co]2+ and [L(CoX2)] (X = OAc, Cl) are high-spin CoII complexes with one or two neutral ligands. A reversible, ligand-based 1e- redox process is observed in the bis-bidentate CoII complexes [(L)2Co]2+ and the acetato complex [2Et{Co(OAc)2}]. The bisguanidino-functionalized dioxolenes (GFD) with their two different coordination sites can be prepared in their protonated catechol form from the protected acetals 1Ac, 2Ac. The catechol form 12H and 22H can be selectively oxidized by oxygen to the quinones 1, respectively 2. Since the free quinones prone to undergo decomposition, stabilization can be achieved by complexation. In the stable mononuclear complexes [1(MIICl2)] with M = Cu, Pd, the (κ2-N,N’)-isomer is exclusively present according to which the heterobinuclear complex [(κ2-N,N’-PdIICl2)10(κ2-O,O’-CuIICl2)] can be prepared specifically by sequential coordination. The heteronuclear CuIIPdII complex crystallizes as a symmetric dimer with Cu-Cl-Cu bridges and in solution an equilibrium with the heterobinuclear monomer can be found. In the homobinuclear Cu complex [(CuIICl2)1(CuIICl2)], a reversible coordination of a CH3CN molecule on the Cu atom of the dioxolene site of GFD 1 is possible. This reversible coordination to the monocationic complex [(CuIICl2)1+•(CuIICl2)]+ triggers an intramolecular metal-ligand electron transfer leading to the formation of the mixed valence complex [(CuIICl2)1(CuIIICl2(CH3CN))]+.