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.

Abstract(η6‐Arene)ruthenium(II) complexes of the type [{[η6‐C6H5(CH2)nCOOH]Ru(µ‐Cl)Cl}2] (2a, n = 1; 3, n = 3) with tethered carboxylate groups can be obtained by dehydrogenation of the appropriate cyclohexadiene with RuCl3·3H2O. Formation of a κO‐coordinated chelate in weakly acidic solution is observed by means of a 1H NMR titration for both [{η6‐C6H5(CH2)3COOH}Ru(aq)](OTf)2 (3a′) and [{η6‐C6H5(CH2)3COOH}Ru(phen)(aq)](OTf)2 (5′). Sandwich complexes of the type [{η6‐C6H5(CH2)3COOH}Ru(η6‐amino acid)](OTf)2 [amino acid = AcpheOH (6), ActyrOEt (7), ActrpOH (8)] can be prepared by treating [{η6‐C6H5(CH2)3COOH}Ru(acetone)3](OTf)2 with the appropriate aromatic bioligand in CF3COOH (6/8) or CH2Cl2 (7). Chemospecific η6‐labelling of the C‐terminal indole function is observed for the peptide HphetrpOH in the analogous complex 9. Quantitative formation of 8 can also be achieved in aqueous solution in the presence of a 3:1 excess of the {η6‐C6H5(CH2)3COOH}RuII fragment. This can also be employed for the N‐terminal labelling of amino acids and peptides in its sandwich complex [(η6‐C6Me6)Ru{η6‐C6H5(CH2)3COOH}](OTf)2 (10). Coupling reactions by the carbodiimide method with EDC afford water‐stable complexes of the type [(η6‐C6Me6)Ru{η6‐C6H5(CH2)3C(O)R}](OTf)2 [R = trpOMe (11), pheOMe (12), glyglyOEt (13)] in good yields. X‐ray structures of [(η6‐C6H5CH2COOC2H5)RuCl(phen)](OTf) (4b′) and 10 are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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.