Four structural isomers of platinum(II) complexes with C-deprotonated R-C^N^N-R’ cyclometallated ligands (R-C^N^N-R’ = -extended 6-aryl-2,2’-bipyridine derivatives containing 2-naphthyl, 3-isoquinolinyl, 1-isoquinolinyl or 2-quinolinyl moieties) have been synthesized with their photophysical properties investigated. The one bearing a 3-isoquinolinyl moiety shows the highest emission quantum yield among the four and hence has been extensively modified to give a series of complexes with different ancillary ligands (chloride, iodide, phenoxide, or acetylide). Most of these complexes show vibronic emission (max = 515–644 nm) with high emission quantum yield (up to unity) in degassed CH2Cl2; one of them has been used for OLED fabrication and shows a maximum EQE of 8.15 % with current efficiency of 25 cd A–1. The photocatalytic properties of these derivative complexes for oxidative tertiary amine functionalization have also been examined. Several highly robust and emissive platinum(II) complexes supported by two types of tetradentate O^N^C^N ligand systems (Φem up to 0.99; Td up to 520 ℃) have been synthesized and show different emission energies (λmax = 482–561 nm). Most of them exhibit excimeric emission in solution state at room temperature which are dependent on the modifications on the tetradentate O^N^C^N ligands. DFT/TDDFT calculations reveal that the metal complex showing the most intense excimeric emission possesses an excimeric excited state with a localized structure, which is unusual for these classes of platinum(II) complexes. Based on this finding, WOLED (ηL(max) = 71.0 cd/A, ηp(max) = 55.8 lm/W, ηExt = 16.5 %, CIE = 0.33, 0.42, CRI = 77) and WPLED (ηL(max) = 17.0 cd/A, ηp(max) = 9.1 lm/W, ηExt = 9.7 %, CIE = 0.43, 0.45, CRI = 78) based on this complex have been fabricated with high efficiency achieved. Palladium(II) complexes containing C-deprotonated R-C^N^N-R’ cyclometallated and pentafluorophenylacetylide ligands exhibit phosphorescence in both solid state and fluid solutions at room temperature with some of them exhibiting aggregation-induced emission (AIE). These complexes have been applied as photosensitizers in light-induced oxidative functionalization of secondary and tertiary benzylic amines as well as in light-induced hydrogen production, with a maximum of 175 turnovers for hydrogen produced. Palladium(II) complexes containing two types of tetradentate dianionic O^N^C^N ligand systems (Systems 1 and 2) have been prepared and show constrasting photophyical properties. A full scale time-resolved spectroscopic analysis has been done on some of these complexes and a platinum(II) analogue. These complexes are found to have similar excited state decay pathway( 〖S_1〗^i→〖S_1〗^f→T) with ΦISC of about unity. The emission efficiency of System 2 complexes is superior to that of System 1 complexes, which is ascribed to the suppression of excited state distortion on the basis of the results of DFT calculations. A lower radiative decay rate of System 2 palladium(II) complexes relative to the platinum(II) analogue has been found, which could be due to their lower spin-orbit coupling constant. One of the palladium(II) complexes has been applied in vacuum-deposited OLEDs with maximum current density, power efficiency and EQE of 20.0 cd A^(-1), 13.6 lm W^(-1) and 7.4 % respectively. In addition, applications of these palladium(II) complexes as photosensitizers for oxidation of secondary amines have been examined. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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Selective 1,2-hydrosilylation of 1,3-dienes is a challenging problem to solve for transition metal catalysis. Butadiene, specifically, would be a useful substrate because 3-butenylsilane products have promise as superior coupling reagents for hybrid organic/inorganic materials synthesis. In this thesis, we describe the first selective 1,2-hydrosilylation of conjugated dienes, including butadiene. / Chemistry and Chemical Biology

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.

No description available.

Systematic kinetic and thermodynamic analyses of the substitution reactions of different Pt(II) complexes with a series of bio-relevant nucleophiles have been investigated as a function of concentration and temperature, using standard stopped-flow and UV–Vis Spectrophotometric methods. For this purpose, five different systems involving squareplanar Pt(II) complexes, viz. (i) mononuclear Pt(II) complexes with tridentate nitrogendonor ligands of varying degree of π-conjugation, and (ii) polynuclear Pt(II) complexes with azine, pyridyl units separated by S, S-S and CH2CH2 spacer groups, and α,ω- alkanediamine bridging ligands were synthesised and characterised by various spectroscopic methods. All substitution reactions of the Pt(II) chlorido complexes of the type [Pt(terpy)Cl]+ were studied in the presence of 10 mM LiCl to prevent spontaneous parallel reaction due to hydrolysis or solvolysis. The substitution reactions of the coordinated water molecules in the dinuclear Pt(II) complexes by thiourea nucleophiles of varying steric hindrance were studied under acidic conditions. The concentration of the nucleophile solution was prepared in 0.1 M NaClO4, at pH 2.0 and always at least 10- fold excess to provide pseudo first-order conditions. The pKa values of the coordinated aqua ligands of the dinuclear Pt(II) complexes were determined by Spectrophotometric acid-base titrations. DFT calculations were also performed in an effort to account for the observed reactivity of homologous analogues in each series of complexes, in terms of NBO charges and energies of frontier molecular orbitals. Substitution reactions of the Mononuclear Pt(II) complexes with tridentate ligands showed reactivity of the complexes is controlled by the π–acceptor characteristics of the chelate ligands. The fused rigid pyridyl system allows electronic interaction between the platinum centre and the pyridyl ligands, because of the extended conjugated π-system. This effect is controlled by how the fused ring system around the terpy moiety is structured. The isoquinoline moiety was found to reduce the effective π-backbonding and the lability of CH3PhisoqPtCl complex compared to 1,10-phenanthroline and terpyridine systems, indicating that isoquinoline ligand is a net σ-donor. The results obtained for the substitution reactions of the diaqua Pt(II) complexes with the thiourea and ionic (Br-, I- SCN-) nucleophiles demonstrate that reactivity increases with decreasing pKa values as well as decreasing distance between the Pt(II)centres. An increase in steric crowding at the Pt(II) centre imposed by the methyl groups on the azine linker decelerates the lability of the aqua ligands. The 1H and 195Pt NMR spectroscopic results confirmed degradation of the aromatic-based bridging ligand from the metal centre. The final cleavage of the complex linkers was only achieved after addition of excessive amounts of thiourea and other strong nucleophiles. The negative activation entropies and second-order kinetics for all the substitution reactions support the Associative mode of substitution mechanism. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

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