Premium
The Dynamic Chemistry of Molecular Borromean Rings and Solomon Knots
Author(s) -
Meyer Cari D.,
Forgan Ross S.,
Chichak Kelly S.,
Peters Andrea J.,
Tangchaivang Nicholas,
Cave Gareth W. V.,
Khan Saeed I.,
Cantrill Stuart J.,
Stoddart J. Fraser
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201001806
Subject(s) - zinc , chemistry , crystallization , metal , crystallography , molecule , denticity , stereochemistry , nuclear magnetic resonance spectroscopy , transition metal , solid state , crystal structure , organic chemistry , catalysis
The dynamic solution equilibria between molecular Borromean rings (BRs) and Solomon knots (SKs), assembled from transition metal‐templated macrocycles, consisting of exo ‐bidentate bipyridyl and endo‐ tridentate diiminopyridyl ligands, have been examined with respect to the choice of the metal template and reaction conditions employed in the synthesis of the metalated BRs, otherwise known as Borromeates. Three new Borromeates, their syntheses templated by Cu II , Co II , and Mn II , have been characterized extensively (two by X‐ray crystallography) to the extent that the metal centers in the assemblies have been shown to be distanced sufficiently from each other not to communicate. The solid‐state structure of the Co II –Borromeate reveals that six MeOH molecules, arranged in a [OH⋅⋅⋅O] hydrogen bonded, chair‐like conformation, are located within its oxophilic central cavity. When a mixture of Cu II and Zn II is used as the source of templation, there exists a dynamic equilibrium, in MeOH at room temperature, between a mixed‐metal BR and a SK, from which the latter has been fractionally crystallized. By employing appropriate synthetic protocols with Zn II or Cd II as the template, significant amounts of SKs are formed alongside BRs. Modified crystallization conditions resulted in the isolation of both an all‐zinc BR and an all‐zinc SK, crystals of which can be separated manually, leading to the full characterization of the all‐zinc SK by 1 H NMR spectroscopy and X‐ray crystallography. This doubly interlocked [2]catenate has been identified retrospectively in recorded spectra, where it was attributed previously to a Borromeate with a Zn II cation coordinated to the oxophilic interior walls of the ensemble. Interestingly, these Zn II ‐templated assemblies do not interconvert in MeOH at room temperature, indicating the significant influence of both the metal template and solvent on the solution equilibria. It would also appear that d 10 metal ions favor SK formation—no evidence of Cu II ‐, Co II ‐, or Mn II ‐templated SKs has been found, yet a 1:0.9 ratio of BR:SK has been identified by 1 H NMR spectroscopy when Cd II is used as the template.