The preparation of new multimetallic materials and the functionalisation of nanoparticles with transition metal units
Creators: name: Naeem, Saira
Publisher: name: Imperial College London
Year: 2012

description: A range of functionalised dithiocarbamates have been prepared and shown to successfully coordinate to a series of transition metal complexes which can then be used as a starting point for further chemistry. The potential to change the physical properties of these dithiocarbamate (DTC) complexes as a whole has been exploited through protonation of amine-terminated compounds. As well as rendering the complexes moderately soluble in water, the protonated terminal amine groups on the pendant arms can serve as protecting groups for acid-sensitive co-ligands from cleavage or unwanted reaction during transformations in the presence of acids. An array of diallyl- and methylallyl-terminated DTC complexes have also been formed. The successful ring-closing metathesis of the diallyl units again demonstrates that the additional centre of reactivity on the pendent arms of the DTC ligand can be utilised, allowing further transformations to be carried out without affecting the rest of the complex. Furthermore, the methodology has been extended to nanoparticles where diallyl DTC units have been shown to stabilise the surface of gold nanoparticles. The study was also expanded to include dithiocarboxylate ligands. Few dithiocarboxylate complexes are known in literature, thus a comparison with the analogous dithiocarbamate species is provided in this report. The first examples of gold(I) complexes of this class of ligand (derived from N-heterocyclic carbenes) have been prepared. The synthesis and characterisation of ruthenium-alkenyl complexes bearing this ligand have also been presented and evidence of a remarkable rearrangement caused by their steric effect has been demonstrated. In addition, it has been shown that imidazolium-2-dithiocarboxylate betaines can be used to form monolayers on the surface of gold nanoparticles. The synthesis and characterisation of the first ruthenium vinyl complexes bearing the related dialkyldithiophosphate ligand, [S2P(OR)2]- are reported here. The resulting compounds demonstrate reactivity which differs significantly from that displayed by the analogous dithiocarbamate and xanthate compounds. Following on from the successful investigations of 1,1-dithio ligands, the scope of these explorations was broadened to explore non-sulphur based linkers. These were employed to prepare multimetallic compounds through the inherent affinity of certain donor combinations for particular metals. Isonicotinic acid was employed to link different metal units to generate heteronuclear bi- and trimetallic systems based on careful consideration of their donor properties towards various transition metals (Ru, Rh, Pd, Pt, Ag and Au). In most cases, the first metal was shown to preferentially bind to the carboxylate moiety, and then the nitrogen of the pyridine ring was used in attempts to coordinate further metals. The synthesis of pentametallic complexes using the isonicotinic ligand (based on a rhodium core) is also presented, including the successful coordination of ruthenium metal units to the carboxylate moiety. The design was extended to explore the palladated tetraphenylporphyrin, [(Pd-TPP)(p-CO2H)4], which illustrated that not only can these metallo-porphyrins be used as a scaffold for the addition of peripheral metal units, but also that further functional group transformations can be carried out on the terminal units. Lastly, having explored the utility of these nitrogen-oxygen mixed-donor ligands in the formation of multimetallic compounds, this approach was extended to the surface functionalisation of silver nanoparticles. The nitrogen donor groups of these ligands were shown to readily bind to the surface of silver colloids, allowing the straightforward attachment of metal units to the surface of these materials.