Synthesis of Isoquinoline-based Terpyridine-like Ligands and Some Metal Complexes
A series of new terpyridine-like (N3) ligands consisting of two isoquinolin-3-yl groups attached to the 2 and 6 positions of a central pyridine have been prepared. The ligands possess substituents at the 4-position of the central pyridine and at the 8-position of each isoquinoline moiety. These isoquinoline substituents (Cl, Br) may be used in further reactions to introduce new functionalities and structural elements. The ligands have been designed with potential for coordination to metal ions through N-donor atoms, potentially forming a cleft upon metal coordination. First, the bifunctional heterocycles 8-chloro-3-acetylisoquinoline and 8-bromo-3- acetylisoquinoline were prepared, characterised and used as building blocks to construct 2,6-bis(8-halo-3-isoquinolyl)pyridines with different aryl substituents at the 4-position of the pyridine. A key construction strategy relies on the synthesis of specific building blocks capable of undergoing a Kröhnke-type reaction to form the pyridine ring. Both 8,8"-dichloro- and 8,8"-dibromo-functionalised ligands have been successfully prepared by this route. Precursors to the 8,8"-dichloro ligand are significantly cheaper and we have focused on further functionalisation of the dichloro ligands due to this advantage. The palladium-catalyzed Suzuki cross coupling reaction has been utilised to install phenyl groups at the 8,8"-positions through substitution at the halo groups to afford 2,6-bis(8-phenyl-3-isoquinolyl)pyridine ligands which may have potential to form molecular tweezers. All ligands have been fully characterised, including some crystallographic structure determinations. The preparation of mono and bis-complexes has been achieved using 1:1 and 1:2 metal-ligand ratios, respectively. Pd(II)Cl and homoleptic Ru(II) complexes have been prepared and characterized. A homoleptic Fe(II) complex has also been prepared. A single crystal X-ray structure of the Fe(II) complex reveals no intramolecular steric hindrance between the phenyl substituents as is seen in the complexes of classical terpyridines bearing phenyl groups at the 6,6"-positions. This observation can be attributed to the greater cavity size gained from modification of the basic structure of the classical terpyridine ligand, such that the pinching effect does not prohibit binding of a second N3-ligand.
Advisor: Lucas, Nigel
Degree Name: Master of Science
Degree Discipline: Chemistry
Publisher: University of Otago
Keywords: terpyridine; terpyridine-like (N3) ligands; isoquinoline; terpyridine-like (N3) ligands and metal complexes
Research Type: Thesis