1,2,5,6-Tetrakis(guanidino)-Naphthalenes: Electron Donors, Fluorescent Probes and Redox-Active Ligands

New redox-active 1,2,5,6-tetrakis(guanidino)-naphthalene compounds, isolable and storable in the neutral and deep-green dicationic redox states and oxidisable further in two one-electron steps to the tetracations, are reported. Protonation switches on blue fluorescence, with the fluorescence intensity (quantum yield) increasing with the degree of protonation. Reactions with N-halogenosuccinimides or N-halogenophthalimides led to a series of new redox-active halogeno- and succinimido-/phthalimido-substituted derivatives. These highly selective reactions are proposed to proceed via the tri- or tetracationic state as the intermediate. The derivatives are oxidised reversibly at slightly higher potentials than that of the unsubstituted compounds to dications and further to tri- and tetracations. The integration of redox-active ligands in the transition-metal complexes shifts the redox potentials to higher values and also allows reversible oxidation in two potentially separated one-electron steps.

Synthesis and crystal structures of non-symmetric 1,3-di(alkyloxy)imidazolium salts

A series of non-symmetric 1,3-di(alkyloxy)imidazolium salts were synthesized by stepwise alkylation of 1-hydroxyimidazole-3-oxide. The quaternary salts were subsequently functionalized by bromination in 2-position. A 2-azidoimidazolium salt and an imidazoline-2-thione were prepared exemplarily. Crystal structures of two 2-bromo-1-alkyloxy-3-methyloxyimidazolium tribromides and a mercury(II)-thione complex have been determined by X-ray diffraction.

1,8-Bis(silylamido)naphthalene complexes of magnesium and zinc synthesised through alkane elimination reactions

The reactions between magnesium or zinc alkyls and 1,8-bis(triorganosilyl)diaminonaphthalenes afford the 1,8-bis(triorganosilyl)diamidonaphthalene complexes with elimination of alkanes. The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and one or two equivalents of MgⁿBu₂ affords two complexes with differing coordination environments for the magnesium; the reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and MgⁿBu₂ in a 1 : 1 ratio affords 1,8-C₁₀H₆(NSiMePh₂)₂{Mg(THF)₂} (1), which features a single magnesium centre bridging both ligand nitrogen donors, whilst treatment of 1,8-C₁₀H₆(NSiR₃H)₂ (R₃ = MePh₂, ⁱPr₃) with two equivalents of MgⁿBu₂ affords the bimetallic complexes 1,8-C₁₀H₆(NSiR₃)₂{ⁿBuMg(THF)}₂ (R₃ = MePh₂2, R₃ = ⁱPr₃3), which feature four-membered Mg₂N₂ rings. Similarly, 1,8-C₁₀H₆(NSiⁱPr₃)₂{MeMg(THF)}₂ (4) and 1,8-C₁₀H₆(NSiMePh₂)₂{ZnMe}₂ (5) are formed through reactions with the proligands and two equivalents of MMe₂ (M = Mg, Zn). The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and two equivalents of MeMgX affords the bimetallic complexes 1,8-C₁₀H₆(NSiMePh₂)₂(XMgOEt₂)₂ (X = Br 6; X = I 7). Very small amounts of [1,8-C₁₀H₆(NSiMePh₂)₂{IMg(OEt₂)}]₂ (8), formed through the coupling of two diamidonaphthalene ligands at the 4-position with concomitant dearomatisation of one of the naphthyl arene rings, were also isolated from a solution of 7.

Counter-ligand control of the electronic structure in dinuclear copper-tetrakisguanidine complexes

Decision-making counter-ligands: a bridging redox-active ligand in a dinuclear copper complex could be either neutral (complex type [Cu^II-GFA-Cu^II]) or dicationic (complex type [Cu^I-GFA-Cu^I]), depending on the nature of the counter-ligands X.