'Click' Chemistry in Coordination and Supramolecular Chemical Applications

The term “click chemistry” was first coined by Sharpless and co-workers in 2001 and encompasses a range of high yielding organic coupling reactions which are rapid, highly selective and proceed with good functional group tolerance.
Furthermore the reaction conditions are mild and require minimal workup and product purification. The most prominent example of these reactions is the copper catalysed alkyne/azide cycloaddition (CuAAC) for the formation of 1,4- disubstituted-1,2,3-triazoles. CuACC has been utilised in a variety of chemical disciplines including organic synthesis, the modification of biological macromolecules and in polymer and materials chemistry. More recently this reaction has shown a growing interest from the inorganic community for the design of new ligands for transition metal complexes and their supramolecular assemblies.

In this thesis, I present my results on the use of the 'click' chemistry in coordination and supramolecular chemical applications.

Described in chapter 3 is the synthesis of 1,4 disubstituted-1,2,3-triazole ligands which can act as either axial monodentate ligands, through the N3 atom of the triazole ring, or as bidentate N^N donor ligands if a pyridyl substituent is incorporated into a chelate ligand framework. The photophysical effects of these ligands were investigated on rhenium tricarbonyl complexes. It was found that replacing the Cl- ligand by the triazole stabilises the energy of the HOMO with respect to the LUMO and results in a blue shift of the emission maximum whilst changing the bidentate ligand by replacing the bipyridyl ligand by pyridinetriazole ligand elevates the LUMO with respect to the HOMO again resulting in a
blue shift in luminescence.

Described in chater 4 is the synthesis of 4-azido-2,2’-bipyridyl and 4,4’-diazido-2,2’-bipyridyl ligands and the CuAAC modification thereof. 4-azido-2,2’- bipyridyl was incorporated in to [Ru(p-cymene)( 4-azido-2,2’-bipyridyl)Cl]+ type
complexes. The CuAAC reaction was utilised to hemically modify the periphery of a metal complex hen an azido substituted ligand is allowed to react with a range of alkynes. Through this approach a second metal binding domain can
easily be introduced upon reaction with 2-pyridyl acetylene. [Ru(p-cymene)( 4-azido-2,2’-bipyridyl)Cl]+ and “click” chemistry can be used as a potential tool in building metallo-supramolecular species. We have therefore made some of the first steps towards the goal of the development of a general “click” chemistry-based methodology for the construction of functional supramolecular architectures via azide-functionalised transition metal complexes.

Desciribed in chapter 5 is the preperation of 1,2,3-triazole bridged luminescent redox switches. Ruthenium, iridium and rhenium complexes incorporating ferrocenyl-bipyridyl ligand in which the ferrocene unit is tethered to the bipyridyl through a 1,2,3-triazole linkage were prepared. We have developed two potential
luminescent switches with ferrocene tagged bipyridyl ligands containing a CuAAC derived triazole linker. The ferrocene moiety quenches the Ru/Ir based luminescent emission, presumably by electron transfer across the triazole bridge. We have demonstrated that the luminescent emission can be switched on by oxidation of the Fc moiety to Fc+.

Described in chapter 6 is the synthesis and characterisation of a range of ligands, incorporating the 1,2,3-triazole moiety, which have designed to act as bridging ligands for the construction of supramolecular assemblies. We have subsequently prepared two dinuclear ruthenium and iridium complexes of the 4-pyridyl-1-(2,2’-bipyrid-4-yl)-1,2,3-triazole bridging ligand, and carried photophysical studies. We have shown that the dinuclear species exhibit greater luminescent intensities than mono-nuclear model complexes because the metal centre coordinated to the pyridine-triazole domain acts as a sensitizer for the metal centre coordinated to the bipyridyl domain through a photoinduced energy transfer mechanism. This shows that there is efficient transfer across the bridging ligand.