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Helical Complexes Containing Diamide‐Bridged Benzene‐ o ‐dithiolato/Catecholato Ligands
Author(s) -
Schulze Isfort Christian,
Kreickmann Thorsten,
Pape Tania,
Fröhlich Roland,
Hahn F. Ekkehardt
Publication year - 2007
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.200601167
Subject(s) - chemistry , ligand (biochemistry) , antiparallel (mathematics) , stereochemistry , crystallography , catechol , benzene , crystal structure , nuclear magnetic resonance spectroscopy , enantiomer , medicinal chemistry , receptor , organic chemistry , biochemistry , quantum mechanics , magnetic field , physics
Abstract The benzene‐ o ‐dithiol/catechol ligands H 4 ‐ 2 and H 4 ‐ 3 react with [TiO(acac) 2 ] to give the dinuclear, double‐stranded anionic complexes [Ti 2 (L) 2 (μ‐OCH 3 ) 2 ] 2− ([ 22 ] 2− , L= 2 4− ; [ 23 ] 2− , L= 3 4− ). NMR spectroscopic investigations reveal that the complex anion [Ti 2 ( 2 ) 2 (μ‐OCH 3 ) 2 ] 2− is formed as a mixture of three of four possible isomers/pairs of enantiomers, whereas only one isomer of the complex anion [Ti 2 ( 3 ) 2 (μ‐OCH 3 ) 2 ] 2− is obtained. The crystal structure analysis of (PNP) 2 [Ti 2 ( 3 ) 2 (μ‐OCH 3 ) 2 ] shows a parallel orientation of the ligand strands, whereas the structure determination for (AsPh 4 ) 2 [Ti 2 ( 2 ) 2 (μ‐OCH 3 ) 2 ] does not yield conclusive results about the orientation of the ligand strands due the presence of different isomers in solution, the possible co‐crystallisation of different isomers and severe disorder in the crystal. NMR spectroscopy shows that ligand H 4 ‐ 3 reacts at elevated temperature with [TiO(acac) 2 ] to give the triple‐stranded helicate (PNP) 4 [Ti 2 ( 3 ) 3 ] ((PNP) 4 [ 24 ]) as a mixture of two isomers, one with a parallel orientation of the ligand strands and one with an antiparallel orientation. Exclusively the triple‐stranded helicates [Ti 2 (L) 3 ] 4− ([ 25 ] 4− , L= 1 4− ; [ 26 ] 2− , L= 4 4− ) are formed in the reaction of ligands H 4 ‐ 1 and H 4 ‐ 4 with [TiO(acac) 2 ]. The molecular structures of Na(PNP) 3 [Ti 2 ( 1 ) 3 ]⋅CH 3 OH⋅H 2 O⋅Et 2 O (Na(PNP) 3 [ 25 ]⋅CH 3 OH⋅H 2 O⋅Et 2 O) and Na 1.5 (PNP) 6.5 [Ti 2 ( 4 ) 3 ] 2 ⋅3 DMF (Na 1.5 (PNP) 6.5 [ 26 ] 2 ⋅3 DMF) reveal a parallel orientation of the ligand strands in both complexes, which is retained in solution. The sodium cations present in the crystal structures lead to two different kinds of aggregation in the solid state. Na‐[ 25 ]‐Na‐[ 25 ]‐Na polymeric chains are formed from compound Na(PNP) 3 [ 25 ], with the sodium cations coordinated by the carbonyl groups of two ligand strands from two different [Ti 2 ( 1 ) 3 ] 4− ions in addition to solvent molecules. In contrast to this, two [Ti 2 ( 4 ) 3 ] 4− ions are connected by a sodium cation that is coordinated by the three meta oxygen atoms of the catecholato groups of each complex tetraanion to form a central {NaO 6 } octahedron in the anionic pentanuclear complex {[ 26 ]‐Na‐[ 26 ]} 7− .