published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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The novel compounds [Pt(trpy)(NCS)]SbF6 (1) and [Pt{4'-(Ph)trpy}(NCS)]SbF6 (2) where trpy = 2,2':6',2''-terpyridine, have been synthesised and characterised by means of elemental analysis, infrared and 1H NMR spectroscopy, and mass spectroscopy. Compounds 1 and 2 were also prepared with the labelled S13C15N¯ ion as co-ligand; their 13C and 15N NMR spectra recorded at room temperature in CD3CN show that the ambidentate ion is coordinated to the Pt atom mainly (~ 95%) through the N atom, but that a small amount of the S-bound isomer also co-exists in an acetonitrile solution. The synthesis of 1 is preceded by the isolation of yellow 1·CH3CN?Y (Y = yellow) for which the crystal structure has been determined by single crystal X-ray diffraction; this shows that the SCN¯ ion is linearly bound to the Pt atom through the N atom in the solid state, and that the cation is planar. The solvate rapidly loses acetonitrile to form maroon 1-M (M = maroon). The maroon compound exhibits 3MMLCT (metal-metal-to-ligand charge transfer) emission in the solid state as evidenced by a red-shift in the emission maximum from 653 nm at 473 K to 770 nm at 80 K. However, there are anomalous changes in the emission intensity below 200 K; this phenomenon is explained in terms of competitive emission by defect sites in the material. Interestingly, 1-M displays thermochromic behaviour (accompanied by phase changes at Ts > 473 K) that have been documented over the temperature range 80-548 K by means of photography, emission spectral and powder X-ray diffraction measurements. Compound 1-M also exhibits selective and reversible vapochromic behaviour with acetonitrile, DMF and pyridine – the solvates are yellow. We also report solvent specific changes in the emission spectra between 1-M and its acetonitrile, DMF and pyridine solvates. The thermo- and vapochromism of 1-M are linked to the making and breaking of metallophilic Pt...Pt interactions that occur when the planar cations slide in and out of different positions with respect to each other in a π-stack. Single crystals of compound 2 are isolated by desolvation of single crystals of 2·CH3CN. The single-crystal to single-crystal transformation is easily reversed by exposing 2 to vapours of acetonitrile, as confirmed by X-ray structure determinations of 2 and 2·CH3CN performed on the same single crystal. These show that the SCN¯ ion is linearly bound to the Pt atom through the N atom and that the cation is nearly planar. Significantly, there are only very small changes in the cation and anion atom positions between 2 and 2·CH3CN; thus, single crystals of 2 have a porous metal-organic structure with solvent accessible voids/channels. As such, 2 also sorbs methanol and acetone molecules from the vapour phase, the former without loss of single crystallinity, as confirmed by an X-ray crystal structure determination of 2·CH3OH. Single crystals of 2·(CH3)2CO were obtained by direct crystallization from acetone and an X-ray structure determination performed. Interestingly, a single crystal 2·(CH3)2CO desolvates under ambient conditions to give a single crystal of 2 with the original porous metal-organic crystal structure; on the other hand 2·CH3OH does not readily desolvate because of O─H◦◦◦S hydrogen-bonding. Compound 2 and its solvates are yellow, as expected, since the planar cations hardly move on solvent uptake – in marked contrast to the easily moved cations in 1─M – suggestions as to why are given. Finally, we report the solid state photoluminescence (measured at 77 K) of 2, 2·CH3CN, 2·CH3OH, 2·(CH3)2CO and 2·CH3OH_DS where DS denotes desolvation of the methanol solvate. Emission from 2 is characterised by dual emission from 3MLCT (metal-to-ligand charge transfer) and excimeric 3(π-π*) excited states; with the latter being the predominant origin of emission at 77 K. On the other hand, the 2·CH3CN and 2·(CH3)2CO solvates give well defined monomeric 3MLCT emission exclusively. The excimeric emission is representative of the cation packing arrangement in the crystal lattice, and the fact that it is not observed for 2·CH3CN and 2·(CH3)2CO is probably a result of an increase in the potential energy barrier to the formation of excimers when free space is occupied by CH3CN or (CH3)2CO included in the crystal lattice. Emission by 2·CH3OH and 2·CH3OH_DS is further complicated by 3MMLCT emission that arises because of dz2(Pt)-dz2(Pt) orbital interactions present in the solid. As a result multiple emission from 3MLCT, excimeric and 3MMLCT excited states is observed for 2·CH3OH and 2·CH3OH_DS. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

A novel platinum(II) complex, [Pt{4-(o-tolyl)-6-(3˝-isoquinoyl)-2,2´-bipyridine}Cl]SbF6 (Pt4) was synthesized and characterised by means of infrared, elemental analysis, mass spectroscopy, and NMR spectroscopy. Substitution kinetics of chloride ligand from square planar platinum(II) complexes namely; [Pt(2,2´:6´,2˝-terpyridine)Cl]Cl·2H2O (Pt1), [Pt{2-(2´-pyridyl)-1,10-phenanthroline}Cl], (Pt2), [Pt{4´-(o-tolyl)-2,2´:6´,2˝-terpyridine}Cl]CF3SO3 (Pt3) and [Pt{4´-(o-tolyl)-6-(3˝-isoquinoyl)-2,2´-bipyridine}Cl]SbF6 (Pt4) were studied using a series of five-membered heterocyclic neutral nitrogen donor nucleophiles, viz. pyrazole (Pz), triazole (Tz), imidazole (Im), 1-methylimidazole (MIm) and 1,2-dimethylimidazole (DMIm) under pseudo first-order conditions in methanol. The kinetics of the substitution reactions were studied as a function of concentration of the nucleophiles at different temperatures using UV/Visible spectrophotometry and conventional stopped-flow techniques. The observed second-order rate constants, k2 followed a two term rate law kobs = k2[Nucleophile] + k-2 except for 1,2-dimethylimidazole with Pt1, Pt3, Pt4 and Pz and Tz with Pt1. The observed second-order rate constants along with the negative entropies of activation support an associative mode of substitution behaviour. The results obtained indicate that increasing the π-conjugation in the cis and cis/trans position influences the rate of substitution reactions. Increasing the π-conjugation in the cis position decreases the rate of the substitution reactions by decreasing the π-acceptor property of the terpy moiety. On the other hand, increasing the π-conjugation in the cis/trans position increases the rate of substitution reaction by enhancing the π-acceptor property within the ligand framework. This in turn increases the electronic communication, which consequentially decreases the frontier orbital energy gap between HOMO and LUMO and hence increases the reactivity of the metal centre. Thus the observed trend for the reactivity was Pt2 > Pt1 > Pt3 > Pt4. The observed kinetic trend was further supported by DFT-calculations obtained from the computational analysis carried out for the complexes. The substitution kinetics was influenced by the basicity of the incoming nucleophiles. Except for the sterically hindered nucleophile, DMIm, the pKa of the entering nucleophiles followed a Linear Free Energy Relationship (LFER) indicating an increase in the substitution reactions with increase in the basicity of the nucleophile. The general trend observed for the reactivity of the nucleophiles is MIm > Im > DMIm > Pz > Tz. In the reverse reactions the replacement of the azoles by the chloride was controlled by the strength of the Pt—N(azole) bond which is dependent on the strength of the extent of the π-back-bonding between the platinum centre and the azole. / Theses (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

The synthesis of several new phosphorus derivatives including new monophosphanes of the type RPX(_2) (X = F, CI and H), containing either the Fluoromes [2,4,6-(CF(_3))(_3)C(_6)H(_2)] or Fluoroxyl [2,6-(CF(_3))(_2)C(_6)H(_3)] group has been carried out successfully. The synthesis of a number of Cis-Platin analogous has been facilitated by the reaction of these new monophosphanes with a platinum dimer [(PCl(_2)(Pet(_3))(_2)](_2). These compounds are of the type PtCl(_2)(Pet(_3))RPX(_2) (X = CI, H and F, R = 2,6- bis(trifluoromethyl)phenyl). These compounds have shown an interesting correlation between bond length and (^1)J(_p-pt) NMR coupling. Disubstituted phosphanes (RPX(_2), X = CI, H) have also been synthesised and subsequent reaction has facilitated the formation, characterisation and structure solution of a new phosphorus (I) species (RP(_2)(^(-)))(Ph(_3)PCH(_3))(^1) (R - Fluoromes).Attempts have been made to synthesise the first phosphaalkyne containing a bulky electron withdrawing ligand. This involved the reaction of RP=CCl(_2) (R = 2,6- bis(trifluoromethyl)phenyl) with a number of Pt(0) and Pd(0) species. (^31)P NMR studies have been used extensively throughout the project to help characterise and identify the products. The single crystal, solid state structures of many of the new species were elucidated by X-ray diffraction using a Siemens Smart CCD.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

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

published_or_final_version / Chemistry / Master / Master of Philosophy