SELF-ASSEMBLY OF DINUCLEAR CH2-BRIDGED TITANIUM(IV) CATECHOLATE COMPLEXES - INFLUENCE OF THE COUNTERIONS AND OF METHYL SUBSTITUENTS IN THE LIGAND/

Authors
Citation
M. Albrecht, SELF-ASSEMBLY OF DINUCLEAR CH2-BRIDGED TITANIUM(IV) CATECHOLATE COMPLEXES - INFLUENCE OF THE COUNTERIONS AND OF METHYL SUBSTITUENTS IN THE LIGAND/, Chemistry, 3(9), 1997, pp. 1466-1471
Citations number
67
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
Chemistry → ACNP
ISSN journal
0947-6539
Volume
3
Issue
9
Year of publication
1997
Pages
1466 - 1471
Database
ISI
SICI code
0947-6539(1997)3:9<1466:SODCTC>2.0.ZU;2-#
Abstract
The spontaneous self-assembly of methylene-bridged dinuclear Ti-IV com plexes M-4[L3Ti2] (L = 1-3) from CH2-bridged di(catechol) ligands (1-H -4-3-H-4) was found to proceed in the presence of lithium or sodium ca rbonate acting as a base (M = Li, Na). In contrast, only an unspecific mixture of coordination compounds was obtained in the presence of pot assium carbonate. This difference in behavior is due to the ability of Li+ or Na+ to stabilize the triple-stranded dinuclear titanium(IV) sp ecies [L3Ti2](4-). In the solid state, Li-4[(1)(3) Ti-2] exhibits a hi ghly symmetric structure with three lithium cations bound to the meso- helicate tetraanion. Li-6 NMR together with H-1 NMR studies at variabl e temperature revealed that, in solution, an unsymmetrical ''bowl-shap ed'' species is formed with only two Li+ bound to the anion. A methyl substituent on the methylene spacer of the di(catechol) ligand (ligand 2) led to supramolecular systems with new stereocenters and thus a hi gher content of information. However, only one of the four possible di astereoisomeric metal complexes of [(2)(3) Ti-2](4-) was observed. A t hird type of ligand, with a methyl group attached to one terminus of t he linear ligand, was also investigated. The synthesis of such an unsy mmetrical ligand, 3-H-4, was readily achieved starting from 2,3-dimeth oxybenzyl alcohol (4) and 2,3-dimethoxybenzaldehyde (6). Upon complexa tion, the ligand 3-H-4, led to a statistical mixture of the two possib le isomers of the dinuclear titanium(IV)complex [(3)(3) Ti-2](4-).