Ring inversion in polycyclic tetraamines

A benzimidazole functionalised DO3A chelator showing pH switchable coordination modes with lanthanide ions

“…27 The glyoxal bridged bis-aminal cyclen compound (cis-13-1,4,7,10-tetraazatetracyclo[5.5.2.0 4,14 0 10,13 ]tetradecane) was isolated in 88% yield. [28][29][30] The bis-aminal cyclen derivative was employed in a reaction with 2-chloromethyl benzimidazole to form the quaternized product 3. 31,32 The reaction was carried out in acetonitrile with stirring at RT for 8 days and then evaporated to dryness to yield 3 as a solid.…”

Synthesis and X-ray Crystal Structure Determination of the First Transition Metal Complexes of the Tetracycles Formed by Tetraazamacrocycle−Glyoxal Condensation: PdL*Cl2 (L = Cyclam−Glyoxal Condensate (1), Cyclen−Glyoxal Condensate (2))

“…Tetraazamacrocycles are famously prolific ligands for transition and other metal ions, adopting numerous geometries and binding modes. Countless derivatizations of the monocyclic macrocycles cyclam (1,4,8,11-tetraazacyclotetradecane) and cyclen (1,4,7,10-tetraazacyclododecane) alone have produced pendant arm, bicyclic, tricyclic, tetracyclic, and linked forms of these workhorse ligands and their corresponding metal complexes. − Surprisingly, the ability to complex with transition metal ions has not been demonstrated for one well-known type of derivative: − the glyoxal condensation products of the parent tetraazamacrocycles synthesized according to Scheme …”

“…The tetracyclic condensation products of glyoxal and tetraazamacrocycles have been known for over twenty years. − These interesting organic molecules are formed when each aldehyde functional group reacts with two secondary amines of the macrocycle, completing an aminal group and closing a tetracyclic, panel-like molecule. Under most reaction conditions, the methine hydrogens of the two-carbon central bridge in the resulting tetracyclic structures are located cis to each other, giving a folded system of four fused rings. , The trans isomer can be obtained only under certain conditions and gives a more nearly flat structure .…”

Bis‐Aminals of Linear Tetraamines: Kinetic and Thermodynamic Aspects of the Condensation Reaction

“…Identification of the vic/gem configuration was obtained from 13 C NMR spectroscopic data and the recognition of cis/trans isomers was deduced from the temperature dependence of the spectra. The trans isomer is found to stay rigid [7] whereas the cis isomer exhibits a fluxional behaviour consistent with a dynamic process that involves the sequential inversion of the nitrogen atoms and piperazine rings. When needed, for the pyruvic aldehyde derivatives, HMQC, HMBC and COSY sequences were used to elucidate the localisation of the methyl group on the bis-aminal bridge.…”