Double-pillared cobalt Pacman complexes: synthesis, structures and oxygen reduction catalysis.

The syntheses and structures of binuclear cobalt complexes of a double-pillared cofacial Schiff-base pyrrole macrocycle (L) were determined and their activity as catalysts for the oxygen reduction reaction evaluated. The new binuclear cobalt complex, [Co(2)(L)], 1 was formed in good yield using a salt-elimination method and was characterised as adopting a cofacial structure in solution by NMR spectroscopy and as its THF and pyridine solvates in the solid state by X-ray crystallography. Using a variety of spectroscopic techniques, this complex was found to react reversibly with dioxygen to form a new paramagnetic complex.

Selective anion binding by a cofacial binuclear zinc complex of a Schiff-base pyrrole macrocycle.

The synthesis of the new cofacial binuclear zinc complex [Zn(2)(L)] of a Schiff-base pyrrole macrocycle is reported. It was discovered that the binuclear microenvironment between the two metals of [Zn(2)(L)] is suited for the encapsulation of anions, leading to the formation of [K(THF)(6)][Zn(2)(μ-Cl)(L)]·2THF and [Bu(n)(4)N][Zn(2)(μ-OH)(L)] which were characterized by X-ray crystallography. Unusually obtuse Zn-X-Zn angles (X = Cl: 150.

Ligand modifications for tailoring the binuclear microenvironments in Schiff-base calixpyrrole pacman complexes.

The synthesis and structures of two new octadentate, Schiff-base calixpyrrole macrocycles are presented in which modifications at the meso-substituents (L(1)) or the aryl spacer between the two pyrrole-imine donor compartments (L(2)) are introduced. The outcomes of these changes are highlighted in the structures of binuclear Pacman complexes of these macrocycles, [M(2)(L(1))] and [M(2)(L(2))]. Both palladium and cobalt complexes of the fluorenyl-meso-substituted macrocycle H(4)L(1) adopt rigid, but laterally twisted geometries with enclosed bimetallic microenvironments; a consequence of this spatial constraint is an exo-exo-bonding mode of pyridine in the dicobalt complex [Co(2)(py)(2)(L(1))].

Synthesis of mono-, di- and tetra-alkyne functionalized calix[4]arenes: reactions of these multipodal ligands with dicobalt octacarbonyl to give complexes which contain up to eight cobalt atoms.

The functionalized mono-alkyne cone-monopropargyl p-tert-butylcalix[4]arene was synthesized by the reaction of p-tert-butylcalix[4]arene with K(2)CO(3) and 3-bromo-1-propyne. More prolonged reaction times led to the formation of the 1,3 cone bis(propargyl)calix[4]arene . The tetra-alkyne species cone-tetrapropargyl p-tert-butylcalix[4]arene and its conformational isomer, 1,3-alternate-tetrapropargylcalix[4]arene may both be prepared via related reaction sequences.