Capsule formation, carboxylate exchange, and DFT exploration of cadmium cluster metallocavitands: highly dynamic supramolecules.

A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests.

Zinc carboxylate cluster formation in conjugated metallomacrocycles: evidence for templation.

A new [3 + 3] Schiff base macrocycle incorporating three N2O2 salphen-type binding sites and peripheral neopentyloxy substituents has been prepared. The incorporation of Zn2+ ions into this and related conjugated Schiff base macrocycles has been studied by NMR spectroscopy, mass spectrometry, and X-ray diffraction. When reacted with 7 equiv of zinc acetate, the macrocycles template the formation of heptanuclear complexes.

Heptametallic bowl-shaped complexes derived from conjugated Schiff-base macrocycles: synthesis, characterization, and X-ray crystal structures.

The reaction of chelating conjugated macrocycles 1a-c with Zn(OAc)2 gives bowl-shaped heptanuclear Zn complexes featuring Zn in tetrahedral, octahedral, and square-pyramidal geometries. Crystallographic and NMR results indicate that vacant Zn coordination sites within the bowl may be accessed, suggesting that these coordination complexes may be used as mimics for Zn fingers and carbonic anhydrase.

Synthesis, structure, and computational studies of soluble conjugated multidentate macrocycles.

[Chemical reaction: See text] Conjugated, shape-persistent macrocycles based on [3 + 3] Schiff-base condensation are of interest for supramolecular materials. In an effort to develop new discotic liquid crystals based on these compounds, a series of macrocycles with peripheral alkoxy groups of varying length have been prepared. The synthesis and mechanism of formation have been probed by isolation of oligomeric intermediates.

Tautomerization in naphthalenediimines: a keto-enamine Schiff base macrocycle.

[reaction: see text] A new [3 + 3] Schiff base macrocycle incorporating naphthalene groups has been prepared. By examination of its properties, X-ray crystallography of model compounds, and calculations, it has been determined that the macrocycle exists predominantly as the keto-enamine tautomer. This unexpected tautomerization presents an unusual hexaketo interior in the macrocycle.

Mild and selective reduction of imines: formation of an unsymmetrical macrocycle.

During investigations of 5, a [3 + 3] Schiff-base macrocycle with six imines, a partially reduced Schiff-base macrocycle, 6, possessing one CH(2)NH and five imine groups was obtained. Control experiments and deuterium labeling indicate that the macrocycle is reduced by a benzimidazoline generated during the reaction. Benzimidazolines may be convenient reagents for the mild and selective reduction of imines.

Cyclopentadienyl benzamidinato chromium complexes as models for alkyl halide activation by chromium reagents.

Cyclopentadienyl complexes of Cr(II) and Cr(III) are stabilized by bis(trimethylsilyl)benzamidinato ligands, allowing the resulting well-defined compounds to serve as models for alkyl halide activation by mid-valent Cr-based reagents.