Pairing of Propellers:  Dimerization of Octahedral Ruthenium(II) and Osmium(II) Complexes of Eilatin via π−π Stacking Featuring Heterochiral Recognition

Abstract

Five octahedral eilatin complexes of the type [M(L-L)(2)(eilatin)](2+) (M = Ru, Os; L-L = bipyridyl-type ligands) were synthesized, and their dimerization via pi-pi stacking was studied by crystallography and (1)H NMR techniques. The X-ray structures of these racemic complexes were solved and revealed that the eilatin complexes are organized as discrete dimers in which the eilatin residues of each complex are stacked in centrosymmetric packing. Chemical shift dependence on concentration in the (1)H NMR spectra support fast dimer-monomer equilibrium, and the structures of the dimers in acetonitrile solution are proposed to be analogous to their solid-state structures. Dimerization constants in acetonitrile were measured for the five racemic eilatin complexes that exhibit different structural parameters, as well as for the two enantiomeric forms of one of these complexes. They were found to be independent of the metal (Ru vs Os), strongly dependent on the steric effects introduced by the L-L ligands (2,2'-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,2'-biquinoline), and dependent on the optical purity of the complexes. A clear preference for heterochiral over homochiral dimer formation was demonstrated. This is the first report of chiral recognition in solution, exhibited by simple chemical systems held solely by pi-stacking interactions.

Supramolecular activation of a molecular photocatalyst

“…7 The planar ligand structure has previously been utilized for detailed dimerization studies of the related mononuclear ruthenium complex [Ru(bpy) 2 (tpphz)](PF 6 ) 2 in solution. [29][30][31][32][33] More recently the DNA intercalation of tpphz-based Ru complexes has been utilized to access reversible luminescent switches.…”

Efficient Asymmetric Synthesis of Δ‐ and Λ‐Enantiomers of (Bipyridyl)ruthenium Complexes and Crystallographic Analysis of Δ‐Bis(2,2′‐bipyridine)(2,2′‐bipyridine‐4,4′‐dicarboxylato)ruthenium: Diastereoselective Homo‐ and Heterochiral Ion Pairing Revisited

“…In contrast to the results outlined above, heterochiral association (∆,Λ) was found to be strongly favored. [10] In order to investigate this ion-pairing phenomenon, we decided to prepare the optically pure dicationic (bipyridyl)-Ru II complexes ∆-and Λ-[Ru(bpy) 2 (cmbpy)][PF 6 ] 2 (3a, b; cmbpy ϭ 4Ј-methyl-2,2Ј-bipyridine-4-carboxylic acid) and ∆-and Λ-[Ru(bpy) 2 (dcbpy)][PF 6 ] 2 (4a, b; dcbpy ϭ 2,2Ј-bipyridine-4,4Ј-dicarboxylic acid), with C 1 and C 2 symmetries, respectively. We anticipated that association of our model complexes with the ∆-Trisphat anion of D 3 symmetry should be the ideal probe to discriminate between homochiral and heterochiral ion-pairing association.…”

2,11‐Dialkylated 1,12‐Diazaperylene Copper(I) Complexes: First Supramolecular Column Assemblies by π‐π Stacking between Homoleptic Tetrahedral Metal Complexes, Exhibiting Low‐Energy MLCT Transitions

“…[5] The octahedral mono(eilatin) Ru II and Os II complexes [M(L-L) 2 (eil)] 2+ (M = Ru, Os; L-L = bipyridyl-type ligands) dimerize by π-π stacking between the eilatin moieties in the solid state and in solu- [ tion. [6] In all the solid-state structures, a well-defined discrete dimer is observed in which the eilatin surfaces are about 3.4 Å apart, a typical distance for systems held by π-π stacking interactions. [7] Scheme 1.…”