The rational synthesis of an octahedral coordination capsule in which the triangular faces are covered by single ligands is described herein. Starting with tris(2-hydroxybenzylidene)triaminoguanidinium chloride [H(6)L]Cl, we observed an oxidative cyclization of this ligand in the presence of PPh(4) (+) ions resulting in the complex [Pd(H(2)L')(PPh(3))] (1). The use of 5,5-diethylbarbiturate (bar(2-)) as a bridging ligand in the presence of [Co(en)(3)](3+) (en=ethylenediamine) leads to the formation of a rectangular box with the formula (Et(4)N)(6)[[Co[(PdCl)(Pd)L](2)(mu-bar)](2)] (2). The analysis of the architecture of compounds 1 and 2 enables the development of a self-assembly strategy for the synthesis of an octahedral coordination cage 3 with the formula Na(4)(Et(3)NH)(12)[(Pd(3)L)(8)[mu-(bar)](12)].x H(2)O. Compound 3 was characterized by (13)C-MAS-NMR spectroscopy and single-crystal structure analysis.
Guanidine‐based ligands can be prepared by a very simple synthesis. These ligands are amenable, in principle, to wide variation and in the anionic form are able to bind three metal centers simultaneously at chelating sites in close proximity (see picture). An oligomer which contains 24 Cd centers, 12 of the ligands shown, and 6 ligands isomeric to them and which forms a doughnutlike ring with a diameter of >30 Å has been characterized.
The fourfold Sonogashira cross-coupling reaction is described as efficient synthetic tool for the preparation of calixarenes with relatively deep electron-rich cavities. Reactions of halocalixarenes with terminal alkynes led to coupling products in yields up to 95 %. Two synthetic pathways to the tetraethynylcalixarene 5 were elaborated and their efficencies were compared. This calixarene was used for the synthesis of the three isomeric tetrakis(pyridylethynyl) compounds 10a-c, which were tested as hosts for the binding of pyridin-
According to plan: C2‐ and C3‐symmetric ligands are essential to the rational design of a low‐symmetry coordination cage with the outer shape of a trigonal bipyramid (view along the C3 axis shown; green: Pd, red: ligand, blue: 5,5‐diethylbarbiturate). The characterization of an intermediate gives insight to the mechanism of formation.
In this article we describe the synthesis, characterisation and metal binding properties of tris(5-bromo-2-hydroxybenzylidene)triaminoguanidinium chloride [H 6 Br 3 L]Cl (1), which can be seen as a triangular building block for supramolecular chemistry. 1 crystallises either in a triclinic (1a) or a rhombohedral (1b) system depending on the used solvent . The pure ligand adopts a conformation unfavourable for the coordination of metal centres, but in the presence of a base or a basic metal salt, a change in the conformation can be observed.
Herein we describe the importance of side chains in C3-symmetric ligands in supramolecular chemistry. The reaction of the new ligand tris(5-bromo-2-methoxybenzylidene)triaminoguanidinium chloride [H3Me3Br3L]Cl (1) with ZnCl2 results in the formation of the monomeric complex (Et3NH)2[(ZnCl2)3Me3Br3L] (2), in which the ligand remains in a conformation less favourable for the coordination of metal centres. The use of the related tris(5-bromo-2-hydroxybenzylidene)triaminoguanidinium chloride, [H6Br3L]Cl, under similar conditions, results in the formation of two different dimeric compounds (NH4)[{[Zn(NH3)]3Br3L}2{mu-(OH)}3]1/4MeOH (3) and [Zn{Zn2(OH2)3(NH3)Br3L}2] (4), depending on the solvent mixture used. The comparable reaction of the ligand tris(5-bromo-2-hydroxy-3-methoxybenzylidene)triaminoguanidinium chloride [H6(OMe)3Br3L]Cl (5), leads to the formation of a doughnut-shaped, protein-sized coordination oligomer (Et3NH)18[{Zn[Zn2Cl{(OMe)3Br3L}]2}6(mu-Cl)6(OH2)6]x CH3CN (6), which comprises six dimeric [Zn5{(OMe)3Br3L}2] units. Whereas 3 and 4 decompose in DMSO solution, 6 is surprisingly stable in the same solvent.
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