The design and synthesis of bridging para-dioxolenes : towards functional metallosupramolecular structures

• Main Author: Caldwell, Sharon Lindsay
• Other Authors: Hicks, Robin Gary
• Language: English; en
• Published: 2010
• Subjects: organic compounds; magnetic materials; UVic Subject Index::Sciences and Engineering::Chemistry
• Online Access: http://hdl.handle.net/1828/2331

A series of para-dioxolene bridging ligands with bis-tridentate or bis-bidentate coordination pockets have been prepared. These ligands were designed to serve as building blocks in the preparation of functional metallosupramolecular structures. The bis-tridentate dipyridyl-diazaanthraquinones have topologies suitable for the preparation of [2 x 2] grids or larger extended structures. Employing a double condensation reaction between 1,3-diamino-4,6-benzenedicarboxaldehyde and 2-acetyl pyridine successfully afforded a cisoid binding diazaanthraquinone. The redox activity of the latter revealed it is more easily reduced than structurally similar 1,5- and 1,8-diazaanthraquinones. The synthesis of an analogous ligand displaying transoid coordination pockets proved challenging. Several approaches were attempted however the preparation of key intermediates 1,4-dinitro-2,5-benzenedicarboxaldehyde and 2,5-diamino-1,4-(hydroxyI-methyl) benzene were unsuccessful. A collection of bis-bidentate 2,5-bis(phosphino)1,4-dioxolenes were prepared with diphenyl, diisopropyl and diethoxy substituents at the phosphorus center. 2,5- Dibromo-1,4-dimethoxybenzene was reacted with the appropriate chlorophosphine under lithiation conditions to afford the dimethoxy compound, which was subsequently deprotected to the hydroquinone state with a Lewis acid. The diphenylphosphino hydroquinone was oxidized using phenyliodonium bisacetate, however efforts to oxidize other hydroquinone precursors to the targeted quinone state proved challenging. Diphenyl and diisopropyl phosphino hydroquinones were successfully coordinated with diamagnetic palladium hexafluoroacetylacetonate precursors. The resulting bimetallic bis(phosphino) dianion complexes were subsequently oxidized to the semiquinone state using silver (I) hexafluorophosphate and studied to determine the distinctive features of the semiquinone ligand.