A Self‐Complementary Assembly of Metallamacrocycles Directed by RuCl⋅⋅⋅HN Hydrogen Bonds and Its Reversible Dichotomy by Halide Anions in Solution

Abstract

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...

Two N,N′-bis(pyridin-4-yl)pyridine-2,6-dicarboxamide coordination compounds

“…A search of the Cambridge Crystallographic Database (CSD, version 5.39, update May 2018; Groom et al, 2016) reveals eight structures with the H 2 L 1 skeleton. These include the methyl pyridinium compound of H 2 L 1 (Dorazco-Gonzá lez et al, 2010), two Ru + compounds (Park et al, 2006;Mishra et al, 2012), two Pd 2+ compounds (Qin et al, 2002(Qin et al, , 2003 and two Co 2+ compounds (Singh et al, 2010(Singh et al, , 2011. There is only one Mn 2+ coordination compound (Noveron et al, 2003), with bis(hexafluoroacetylacetonato) as an ancillary ligand.…”

Supramolecular chemistry

“…17 This is unusual in that the halide anions on metal ions are often lost during self-assembly processes at the expense of coordinating donor ligands. A further case in point is the report of Park et al who described formation of a tennis ball structure 21 2 that simultaneously exploits co-ordination-directed and anion recognition of metal halides.…”

Platinum(II)‐directed Self‐assembly Loop Complexes for Anion Recognition and Sensing

“…A later report by Park et al . showed that a pyridylamide‐ligand‐bridged Ru(II) cyclic loop complex self‐associates to a dimerized structure by the formation of hydrogen bonds between the amide N─H and Ru─Cl moieties with additional intermolecular π–π and CH–π stabilizing interactions . We envision that the incorporation of a pyridyl‐substituted pyridine 2,6‐dicarboxamide into a positively charged, transition‐metal‐directed, self‐assembled macrocylic framework would bring all the essential elements for anion binding including electrostatic, hydrogen‐bonding, conformation‐matching, and aromatic π–π interactions into one molecule.…”