Post-Assembly Covalent Di- and Tetracapping of a Dinuclear [Fe₂L₃]⁴⁺ Triple Helicate and Two [Fe₄L₆]⁸⁺ Tetrahedra Using Sequential Reductive Aminations

The use of a highly efficient reductive amination procedure for the postsynthetic end-capping of metal-templated helicate and tetrahedral supramolecular structures bearing terminal aldehyde groups is reported. Metal template formation of a [Fe₂L₃]⁴⁺ dinuclear helicate and two [Fe₄L₆]⁸⁺ tetrahedra (where L is a linear ligand incorporating two bipyridine domains separated by one or two 1,4-(2,5-dimethoxyaryl) linkers and terminated by salicylaldehyde functions is described. Postassembly reaction of each of these “open” di- and tetranuclear species with excess ammonium acetate (as a source of ammonia) and sodium cyanoborohydride results in a remarkable reaction sequence whereby the three aldehyde groups terminating each end of the helicate, or each of the four vertices of the respective tetrahedra, react with ammonia then undergo successive reductive amination to yield corresponding fully tertiary-amine capped cryptate and tetrahedral covalent cages