Long-range stereocontrol in the self-assembly of two-nanometer-dimensioned triple-stranded dinuclear helicates.
A series of bisimine-bridged dicatechol ligands 2-H(4)-5-H(4) were synthesized and were used to prepare triple-stranded dinuclear helicate-type complexes with a length of up to more than 2 nm. X-ray structural analyses of Na(4)[(2)(3)V(2)], Na(4)[(3)(3)Ti(2)], Na(4)[(4)(3)Ti(2)], and Na(4)[(5)(3)Ti(2)], as well as temperature-dependent NMR investigations of Na(4)[(4)(3)Ti(2)] and Na(4)[(5)(3)Ti(2)] show that, in the case of the rigid linear ligands 2 and 3, and of the ligand 5, which possesses C(2h) symmetry in its idealized structure, homochiral helicates are diastereoselectively formed. Ligand 4, on the other hand, with idealized C(2v) symmetry, leads with surprisingly high selectivity to the formation of the heterochiral meso-helicate. This is attributed to the ability of ligand 4 to adopt a less-restricted conformation in the meso compound than in the helical complex. NMR investigations indicate that both complex units of Na(4)[(4)(3)Ti(2)] invert (LambdaDelta-->DeltaLambda) simultaneously, while in the case of Na(4)[(5)(3)Ti(2)] a stepwise racemization proceeds.
Albrecht
Markus
M
Institut für Organische Chemie der RWTH, Prof.-Pirlet-Strasse 1, 52074 Aachen, Germany. markus.albrecht@oc.rwth-aachen.de
Janser
Ingo
I
Houjou
Hirohiko
H
Fröhlich
Roland
R
D002396:Catechols / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D007097:Imines / Q000138:chemical synthesis / Q000737:chemistry; D008024:Ligands; D046911:Macromolecular Substances / Q000138:chemical synthesis / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008670:Metals / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis*
D002396:Catechols; D007097:Imines; D008024:Ligands; D046911:Macromolecular Substances; D008670:Metals; D009942:Organometallic Compounds