Inspired by nature’s use of self-assembled systems to carry out virtually all biological processes, chemists have taken to building simplified synthetic systems that mimic the biotic world. Although transition metal-ligand interactions are rarely used for the purpose of biological self-assembly, they have several advantages over other weak noncovalent interactions, such as pronounced directionality and significant strength. These particular attributes have allowed chemists to construct a comprehensive library of self-assembled polygons and polyhedra, using different transition metal-ligand motifs. Many of these supramolecular assemblies possess cavities of defined shape and size, which are able to accommodate guest molecules. It has further been realised that isolation of guest species from the bulk phase can lead to many interesting functions, such as containment, sensing and catalysis. Herein, a new self-assembly strategy has been used to construct novel cyclometalated Pt cages and assembly of the first known [Ir(ppy)2]-based capsule has also been achieved. Chapter 1 includes an introduction to metallosupramolecular assemblies, followed by a comprehensive review of three-dimensional architectures with accessible cavities, their synthetic strategies and applications. Chapter 2 reports on the construction of novel Pt(II)-based trigonal prisms using an unusual, kinetically controlled protocol. By exploiting asymmetric cyclometalated 2-phenylatopyridine based platinum corner units that possess both labile and non-labile cis-coordination sites, trigonal prismatic stereoisomeric architectures have been selectively prepared by altering the sequence of addition of ditopic 4,4′-bipy (4,4′-bipyridine) and tritopic tpt (2,4,6-tris(4-pyridyl)-1,3,5-triazine) molecular structural components using a template free method. Collision-induced-dissociation mass spectrometry experiments were used to differentiate between the structural isomers due to their significantly different fragmentation profiles. Chapter 3 describes the synthesis and characterisation of the first molecular capsule based on an [Ir(ppy)2]+ 90° metallosupramolecular acceptor unit. Initial work focused on pyridine-based donor ligands from which an Ir2L2 metallamacrocycle was assembled. However, when the highly conjugated tpt “panels” were used, due to postulated constraints in the dihedral angle, self-assembly of the Ir6tpt4 octahedral was unsuccessful. The constraints in the dihedral angle were eliminated by swapping pyridine for nitrile-based ligands and following the development of a method to resolve rac-[(Ir(ppy)2Cl)2] into its enantiopure forms, homochiral Ir6tcb4 (tcb = 1,3,5-tricyanobenzene) octahedral capsules where realised. Photophysical studies on the Ircapsules have shown that the ensemble of cooperative, weakly coordinating ligands can lead to luminescence not present in the comparative mononuclear analogues. X-ray crystallographic analysis revealed that the Ir capsules possess cavities large enough to accommodate 4 triflate counterions. Through a series of titration experiments the ability of the capsules to act as anion sensors was also exposed. Further exploration into the host-guest chemistry of the Ir6tcb4 capsule is reported in Chapter 4. Subsequent experiments have shown that self-assembly is highly dependent on the counterions associated with the system. While a number of different anions (OTf-, BF4 -, ClO4 -, PF6 -) facilitate the formation of the same octahedral scaffold, when triflimide was employed as a bulkier counterion, no capsule was observed. On subsequent addition of smaller counterions, such as triflate, the same Ir6tcb4 cage assembles, demonstrating that the anions also act as templates. Kinetic stability experiments, undertook by monitoring the rate of scrambling of the Δ and Λ-[Ir(ppy)2]+ components within the preformed ensembles, show that the Ir capsules are up to 1.4×104 times more stable than their mononuclear analogues. The counter anions were also observed to play a crucial role in the capsule’s stability with measured scrambling half-lives ranging from 4.7 mins with tetrafluoroborate to as long as 4.5 days with triflate. In contrast, the rate of ligand exchange in simple mononuclear complexes, as ascertained using EXSY NMR experiments, was found to be approximately independent of the associated anion.

This thesis reports the studies on the reaction of 1-azabutadienes with PhCH2Re(CO)5 to prepare the cyclometallated azabutadiene tetracarbonyl compounds. Three 1-azabutadienes with different reactivity on the N and C-1 carbons were prepared and their reactions with PhCH2Re(CO)5 were investigated. All the reactions gave a mixture of the cyclorheniated azabutadienes and the isomers of the substituted derivatives formed by substitution by a second azabutadiene. The substituted derivatives as the mixture were always the main products of the reactions and were obtained in good-to-excellent yield even under modified conditions intended to optimise the yield of the cyclorheniated azabutadienes. The yield could not be improved beyond 30 %. Isomerisation of the azabutadiene about the N=C bond provided very rare cis-azabutadiene metal complexes. NMR studies on the mixture of the two isomers and suggested that the product ratio depended on the molar ratio of PhCH2Re(CO)5 in the reaction mixtures. The reactions gave the Re analogues of the products obtained in the corresponding Mn reactions. All the compounds were characterised spectroscopically as well as by microanalysis and examples of all three types were structurally determined by X-ray crystallography. The reactions of the substituted derivative as the mixture of the two isomers with unsaturated molecules including phenyl acetylene, p-methoxyphenyl isocyanide, and phenyl isocyanate and methyl acrylate were investigated.

This thesis describes the synthesis and structural characterisation of cyclometalated heteroleptic bis(tridentate)ruthenium(II) complexes based on [Ru(terpyridine)(1,3-dipyridylbenzene)]PF6, a cyclometalated analogue of [Ru(terpyridine)2](PF6)2. These complexes are investigated photophysically, photochemically and electrochemically, and also studied by computational methods. Electron donating, electron withdrawing and large aryl groups have been incorporated at three different positions, and pyrazol-1-yl or 1,2,3-triazol-4-yl used as the N-heterocycle instead of 2-pyridyl groups, as in the parent complex, [Ru(terpyridine)(1,3-dipyridylbenzene)]PF6. The ligands are substituted at the 4 position of the central benzene or pyridine ring, or attached to the N-heterocycle. The positions of these modifications have been specifically chosen to direct electronic effects into the Ru-C bond, the opposite Ru-N bond or directly into the N-heterocycle to analyze their effect. This has provided an understanding as to which stereoelectronict features are most important with regards to changing the electronic nature of the complex, and thus tuning the properties of these complexes. This proves particularly effective in analysing the energy of the visible absorptions resulting from metal-to-ligand charge transfer and emission energy and its related quantum yield.

No description available.

The synthesis of N-heterocyclic carbene precursors based on the hexahydroimidazo[1,5-a]pyridine and their corresponding cyclometalated platinum(II) carbene complexes is reported. All compounds are fully characterized by standard techniques and additionally X-ray structures could be obtained for three complexes. The photophysical properties of these platinum complexes were investigated by absorption and photoluminescence measurements. All complexes showed strong phosphorescence at room temperature in the sky-blue area with quantum yields of up to 71 %. Additionally, their electrochemical properties were examined by voltammetry experiments. All results were rationalized by quantum chemical DFT calculations (PBE0/6-311G*).

No description available.

Since C^C* cyclometalated Pt(II) complexes with N-heterocyclic carbene (NHC) ligands have been identified as potential emitter materials in organic light-emitting devices (OLEDs), very promising results regarding quantum yields, colour and stability have been presented. Herein, we report on four nitrile substituted complexes with a chelating NHC ligand (1-(4-cyanophenyl)-3-isopropyl-1H-benzo[d]imidazole or 4-(tert-butyl)-1-(4-cyanophenyl)-3-methyl-1H-imidazole) and a bidentate monoanionic auxiliary ligand (acetylacetone or dimesitoylmethane). The complexes have been fully characterized including extensive 2D NMR studies (COSY, HSQC, HMBC, NOESY, 195Pt NMR), three of them also by solid-state structures. Photophysical measurements in amorphous PMMA films and pure emitter films at room temperature reveal the impact of the mesityl groups in the auxiliary ligand, which led to a significant increase of the quantum yield, while the decay lifetimes decreased. The electron withdrawing nitrile groups shift the emission towards blue colour coordinates.

A series of phosphorescent bimetallic platinum(II) complexes is presented, which were synthesized by the combination of bidentate cyclometalated N-heterocyclic carbene ligands and different bridging diphenylformamidinates. The complexes were characterized by standard techniques and additionally two solid-state structures could be obtained. Photoluminescence measurements revealed the strong emissive behavior of the compounds with quantum yields of up to 90 % and emission lifetimes of approx. 2 μs. The effect of the substitution pattern in the bridging ligands on the structural and photophysical properties of the complexes was examined in detail and rationalized by density functional theory calculations (PBE0/6-311G*).

No description available.