ISSN:
0947-6539
Keywords:
alkali metals
;
catechol ligands
;
NMR spectroscopy
;
supramolecular chemistry
;
titanium
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The spontaneous self-assembly of methylene-bridged dinuclear TiIV complexes M4[L3Ti2] (L = 1-3) from CH2-bridged di(catechol) ligands (1-H4-3-H4) was found to proceed in the presence of lithium or sodium carbonate acting as a base (M = Li, Na). In contrast, only an unspecific mixture of coordination compounds was obtained in the presence of potassium carbonate. This difference in behavior is due to the ability of Li+ or Na+ to stabilize the triple-stranded dinuclear titanium(IV) species [L3Ti2]4-. In the solid state, Li4[(1)3Ti2] exhibits a highly symmetric structure with three lithium cations bound to the meso-helicate tetraanion. 6Li NMR together with 1H NMR studies at variable temperature revealed that, in solution, an unsymmetrical „bowl-shaped“ 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 higher content of information. However, only one of the four possible diastereoisomeric metal complexes of [(2)3Ti2]4- was observed. A third type of ligand, with a methyl group attached to one terminus of the linear ligand, was also investigated. The synthesis of such an unsymmetrical ligand, 3-H4, was readily achieved starting from 2,3-dimethoxyben-zyl alcohol (4) and 2,3-dimethoxybenz-aldehyde (6). Upon complexation, the ligand 3-H4 led to a statistical mixture of the two possible isomers of the dinuclear titanium(IV) complex [(3)3Ti2]4-.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030913
