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We have investigated the reactions of chalcogenoureas derived from N -heterocyclic carbenes, referred to here as [E(NHC)], with halogens. Depending on the structure of the chalcogenourea and the identity of the halogen, a diverse range of reactivity was observed and a corresponding range of structures was obtained. Cyclic voltammetry was carried out to characterise the oxidation and reduction potentials of these [E(NHC)] species; selenoureas were found to be easier to oxidise than the corresponding thioureas. In some cases, a correlation was found between the oxidation potential of these compounds and the electronic properties of the corresponding NHC. The reactivity of these chalcogenoureas with different halogenating reagents (Br 2 , SO 2 Cl 2 , I 2 ) was then investigated, and products were characterised using NMR spectroscopy and single-crystal X-ray diffraction. X-ray analyses elucidated the solid-state coordination types of the obtained products, showing that a variety of possible adducts can be obtained. In some cases, we were able to extrapolate a structure/activity correlation to explain the observed trends in reactivity and oxidation potentials.

Chalcogen-based urea compounds supported by a wide range of N-heterocyclic carbenes are synthesised and fully characterised. Coordination of selenoureas is further explored with Group 11 transition metals to form new copper, gold and silver complexes. Single crystal X-ray analyses unambiguously establish the solid-state coordination of these complexes and show that the geometry of a complex is highly influenced by a combination of electronic properties - mainly π-accepting ability - and steric hindrance of the ligands, as well as the nature of the metal, affording a variety of coordination behaviours. In this report, we investigate these phenomena using several experimental methods.

The synthesis, structural and photophysical characterisation of four tricarbonyl rhenium(i) complexes bound to 1,10-phenanthroline and a tetrazolato ancillary ligand are reported. The complexes are differentiated by the nature (hydroxy or methoxy) and position (meta or para) of the substituent attached to the phenyl ring in conjugation to the tetrazole ring. The complexes exhibit phosphorescence emission from triplet charge transfer excited states, with the maxima around 600 nm, excited state lifetime decays in the 200-300 ns range, and quantum yield values of 4-6% in degassed acetonitrile solutions. The nature and position of the substituent does not significantly affect the photophysical properties, which remain unchanged even after deprotonation of the hydroxide group on the phenol ring. The interpretation of the photophysical data was further validated by resonance Raman spectroscopy and time-dependent density functional theory calculations. All the complexes are internalised within cells, albeit to variable degrees. As highlighted by a combination of flow cytometry and confocal microscopy, the species display diffuse cytoplasmic localisation except for the complex with the hydroxy functional group at the para position, which reveals lower accumulation in cells and more pronounced punctate staining. Overall, the complexes displayed low levels of cytotoxicity.

We describe the synthesis and characterisation of a series of new copper and silver complexes with selenourea ligands derived from common and readily-prepared N-heterocyclic carbenes (NHCs). The copper complexes behave somewhat predictably, typically leading to [CuCl(L)] complexes (with two exceptions). The silver complexes display a diverse range of structural motifs, including [AgCl(μ-L)] 2 , [AgCl(L) 2 ], [Ag(L) 2 ] + , [Ag(L) 3 ] + , and [(Ag(L) 2 ) 2 (μ-L)] 2+ species. All new complexes are characterised by multinuclear NMR spectroscopy, and several examples are characterised by X-ray crystallography. This study demonstrates the diversity of coordination behaviour that these selenourea ligands can engage in.

The synthesis and co-ordination chemistry of a new 'bulky yet flexible' N-heterocyclic carbene ("IPaul") is reported. This carbene has spatially-defined steric impact; steric maps show that two quadrants are very bulky while the other two are quite open. The electronic properties of this carbene are very similar to those of other 1,3-diarylimidazol-2-ylidenes. Copper, silver, iridium, and nickel complexes of the new ligand have been prepared. In solution, the ligand adopts two different conformations, while X-ray crystallographic analyses of the transition metal complexes suggest that the syn-conformer is preferred in the solid state due to intermolecular interactions. The copper(i) chloride complex of this new ligand has been shown to be highly-active in the hydrosilylation of carbonyl compounds, when compared to the analogous IPr, IMes, IPr* and IPr*(OMe) complexes.

Experimental studies of the ring-closing metathesis reaction of 1,8-nonadiene and the ROMP reaction of cycloheptene show that the rate of isomerisation is not correlated to the initiation rate of the pre-catalyst, and that the absence of phosphine leads to a greatly increased rate of isomerisation. A range of pre-catalysts and solvents were probed and it is proposed that the isomerisation is mediated by a ruthenium hydride complex; our results are consistent with the rate-determining formation of such a species, which might be trapped in situ by tricyclohexylphosphane.

Initiation rates for Grubbs and Grubbs-Hoveyda second generation pre-catalysts have been measured accurately in a range of solvents. Solvatochromic fitting reveals different dependencies on key solvent parameters for the two pre-catalysts, consistent with different mechanisms by which the Grubbs and Grubbs-Hoveyda pre-catalysts initiate.

A dichotomy in the reactivity of B-H bonds is reported. A bis(N-heterocyclic carbene)-ligated iridium(III) complex can effect rapid deuteration of boronate esters at room temperature with low catalyst loadings; however, borane and 9-BBN both undergo deuteration in the absence of catalyst, and do not react with the iridium complexes. This is proposed to result from the inductive electron-withdrawing properties of the boronic ester substituents. Deuterated boronic esters can be accessed rapidly at room temperature with only very low loadings of iridium catalyst.