The coordination-directed self-assembly approach is an extremely powerful strategy for the synthesis of various 2-and 3D metallasupramolecules and can provide a structural and functional basis for its potential application toward molecular sensing and catalysis by using supramolecular chemistry.[1] In particular, discrete 3D self-assemblies derived from the multiple noncovalent interactions between monomeric metallo-subunits, such as chains, squares, and/or cages, are very intriguing because they are structurally complex but symmetrically simple and synthetically convenient to make. [2] Whereas various functional groups have been utilized for such purposes, little attention has been paid to metal-halide bonds, although they are well known as hydrogen-bond acceptors in molecular recognition and crystal engineering.[3] The halides are usually destined to be eliminated, presumably as a result of limited coordination sites on the metal center for incoming ligands.[1] These facts prompted us to explore the way to get the metal-halide groups to participate in both the coordination-directed and noncovalent self-assembly processes without their abstraction. Considering the molecular library model, [1g] we envisioned that the octahedral geometry of a transition metal might provide a novel approach for the use of metal-halide bonds as a self-assembly motif. For example, octahedral transition-metal centers with axial halide and cisprotecting ligands could serve as a 908 building block. The axial halide, then, may participate in hydrogen bonding with suitably functionalized bridging ligands.Herein, we demonstrate the unprecedented self-complementary dimer of Ru II metallamacrocycles which uses the intact metal-halide bonds in the coordination-directed selfassembly process and its reversible dissociation/association behavior, which is controlled by halide anions in solution.The ligand N,N'-bis(pyridin-4-yl)pyridine-2,6-dicarboxamide (1) was quite suitable for our purpose because it has central amide protons as hydrogen-bonding donors and is well known for bridging two metal centers, thus giving metallamacrocycles.[4] In addition, its bisamide configuration has proven to be very useful in hydrogen-bonding-mediated rotaxane formation [5] and anion recognition [6] with metallasupramolecules. As a precursor for the metal center, [RuCl 2 (PPh 3 ) 3 ] (2) was chosen for its ability to give a transCl 2 -cis-N 2 -cis-P 2 coordination environment around the Ru II center by reaction with a chelating phosphine and N-donor ligands. [7] Stirring equimolar amounts of 1, 2, and 1,3-bis(diphenylphosphino)propane (DPPP) in acetone at room temperature yielded the orange solid of 3 2 in good yield (87 %; Scheme 1).A single-crystal X-ray structure determination of 3 2 unambiguously revealed an interesting supramolecular association between two severely folded molecules of Ru II metallamacrocycle 3 (Figure 1). [8] The folded metallacycles 3, self-complementary monomers of 3 2 , are oriented orthogonally to each other. This orthogonal assembly s...

A facile formal ene reaction of trisubstituted silylallenes with triplet molecular oxygen involving the cleavage of a C(sp2)–H bond has been described.

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