Thesis--Ph. D., University of Hong Kong, 1983.

abstract / Chemistry / Doctoral / Doctor of Philosophy

A library of luminescent cyclometalated gold(III) complexes containing various bis-cyclometalating R-C^N^C ligands derived from 2,6-diphenylpyridine and ancillary alkynyl ligands, [Au(R-C^N^C)(C≡CR’)], has been synthesized. Some of the complexes have been structurally determined by X-ray crystallography. These complexes were found to exhibit intense emission in dichloromethane solution at 298 K, originating from metal-perturbed triplet intraligand (IL) excited states of the R-C^N^C ligand, with substantial charge transfer character from the aryl moiety to the pyridyl ring. In the presence of electron-rich alkynyl ligands, the emission origin could be switched to an alkynyl-to-cyclometalating ligand ligand-to-ligand charge transfer (LLCT) excited state. This class of complexes was also demonstrated to show rich electroluminescence properties as emitters in organic light-emitting devices. In addition, the supramolecular assembly of this class of complexes has also been revealed in gelation studies. N-Heterocyclic carbenes have been incorporated into the gold(III) metal center to prepare a series of luminescent mononuclear and dinuclear gold(III) complexes, [{Au(C^N^C)}n(NHC)](PF6)n and [{Au(tBuC^N^CtBu)}n(NHC)]- (PF6)n (n = 1, 2). The X-ray crystal structures of most of the complexes have been determined. The emissions of these complexes were assigned to originate from the metal-perturbed intraligand excited state of the bis-cyclometalating ligand. One of the C2-bridged dinuclear complexes was found to exhibit two distinct reduction couples, tentatively correlated to the presence of significant intramolecular π-π interaction in the complex. Two novel series of luminescent mononuclear alkynylgold(III) complexes, [Au(C^N)(C≡CR)2] (HC^N = 2-phenylpyridine (Hppy) and derivatives) and [Au(C^N^N)(C≡CR)]PF6 (HC^N^N = 6-phenyl-2,2’-bipyridine and derivatives), have been synthesized. Some of the X-ray crystal structures have been determined. The former class of complexes with bidentate C^N ligands has been observed to show tunable emission spanning across the visible spectrum from 462 to 697 nm. With the exception of [Au(ppy)(C≡C-C6H4-NH2-p)2] which showed a low-energy band originated from a 3LLCT [π(C≡C-C6H4-NH2)→π*(C^N)] excited state, all complexes exhibited vibronic-structured emission bands originated from the intraligand transition of the cyclometalating C^N ligand in dichloromethane solution at 298 K. On the other hand, most of the complexes with the tridentate C^N^N-type ligand have been observed to exhibit vibronic-structured emission bands attributed to the intraligand transition of the C^N^N ligand in low-temperature butyronitrile glass. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

The electronic structure and photofragmentation dynamics of several molecular and cluster anions have been investigated in the gas phase via negative ion velocity-map imaging photoelectron spectrometer combined with tandem time-of-flight (TOF) mass spectrometry. Among others, photoelectron imaging investigation of the halogen- and cyano- substituted methyl radicals and corresponding carbenes has been performed on several mono- and hetero- substituted species – dicyanomethyl and chlorocyanomethyl radicals, ·CH(CN)₂ and ·CHClCN, and corresponding carbenes, NCCCN and CClCN. The results are discussed in comparison with the corresponding dichloro- species, focusing on the divergent effects of the halogen and pseudohalogen (CN) substitutions. A cooperative (captodative) interaction of π-donor Cl and π-acceptor cyano groups favors the increased stability of the CHClCN radical, but a competition of the two substituents is observed in the singlet-triplet splitting of the carbene. The experimental results are consistent with high level ab-initio calculations using the spin-flip approach in combination with the coupled-cluster theory. The C-H bond dissociation energies were determined for several substituted methanes and discussed. Additionally, a practical model is presented for describing the energy dependence of laboratory-frame photoelectron angular distributions in direct photodetachment from (in principle) any molecular orbital using linearly polarized light. A transparent mathematical approach is used to generalize the Cooper-Zare central-potential model to initial states of any mixed character. In the limits of atomic photodetachment or photoionization, the model reproduces the Cooper-Zare formula. In the case of electron emission from an orbital described as a superposition of s- and p-type functions, the model yields the previously obtained s-p mixing formula. The formalism is further advanced using the Hanstorp approximation, valid for anion photodetachment only, whereas the relative scaling of the partial wave cross-sections is assumed to follow the Wigner threshold law. The resulting model can be used to describe the energy dependence of photoelectron anisotropy for any atomic, molecular, or cluster anions. As a benchmark case, we compare the predictions of the p-d variant of the model to the experimental results for NO⁻ photodetachment and show that the observed anisotropy trend is described well using physically meaningful values of the model parameters.

The palladium-mediated cross-coupling of aryl electrophiles and amines (Buchwald-Hartwig amination) has become a widely used method of constructing arylamine frameworks. A crucial aspect of the advancement of this chemistry has been the design of ancillary ligands that are able to promote enhanced reactivity in challenging amination reactions. Despite significant ligand development within the field, challenges in this chemistry remain. Chemoselective aminations, wherein one amine substrate undergoes preferential arylation in the presence of multiple reactive amines has remained an underexplored area of Buchwald-Hartwig amination chemistry. This thesis describes the use of [Pd(cinnamyl)Cl]2 and N-[2-di(1-adamantylphosphino)phenyl]morpholine (Mor- DalPhos) in an extensive study of chemoselective Buchwald-Hartwig aminations, with 62 examples of structurally diverse di-, tri-, and tetraamines obtained in synthetically useful yields at reasonable catalyst loadings (1-5 mol % Pd). The coordination chemistry of [(Mor-DalPhos)Pd] species was also explored, as were complementary chemoselective aminations with the isomeric p-Mor-DalPhos ligand, leading to divergent product formation in some instances. The same [Pd(cinnamyl)Cl]2/Mor-DalPhos catalyst system used in the chemoselectivity study was also employed in a series of Buchwald-Hartwig aminations conducted under aqueous and solvent-free conditions, another underexplored area of this chemistry. A total of 52 amine products were isolated using these methodologies, moderate catalyst loadings (3 mol % Pd), and without the use of any additional additives, co-solvents, or rigorous exclusion of air. The synthesis of low-coordinate palladium complexes featuring both NHC and dialkylchlorophosphine ligands is also discussed herein. These complexes are prepared via a previously unreported and straightforward methodology involving an unusual net PCl bond reductive elimination, and represent a potential new class of pre-catalysts forpalladium-mediated reactions.

The side-on dioxygen adducts of N-heterocyclic carbene (NHC) containing rhodium complexes, [ClRh(IPr)2(O2)] and [ClRh(IMes)2(O2)], previously synthesized in our laboratories possess a square planar geometry and O-O bond lengths of 1.323(3) and 1.341(4) Å, respectively. Both of these attributes are uncharacteristic of Rh(O2) complexes, which are typically octahedral and possess O-O bond lengths of approximately 1.45 Å. Full characterization by NMR, IR, Raman, DFT and XAS confirmed the short O-O bond lengths of these structures and revealed that they were rhodium(I) coordination complexes of singlet oxygen with no net oxidation/reduction process having taken place. The unique bonding mode appears to result from the interaction of a filled Rh d orbital with one of the two degenerate O2 * orbitals, which causes splitting of the O2 * orbitals, favoring spin pairing in the O2 HOMO, and the inability of Rh to donate electron density to the empty * orbital. Initial investigations of these complexes as catalysts for the reduction and oxidation of C-O bonds, as well as singlet oxygen generation were also undertaken. Rh(IPr)2 coordination complexes of N2, H2 and CO were also synthesized and characterized by X-ray crystallography, NMR and elemental analysis. Interestingly, the addition of hydrogen gas to rhodium did result in oxidation of the metal. A Rh(NHC) complex featuring an anionic acetate ligand, [(AcO)Rh(IPr)(CO)2], was synthesized and characterized by NMR, IR and X-ray crystallography. This complex proved to be an effective catalyst for the regioselective hydroformylation of aliphatic and aromatic alkenes, which occurred without isomerization of the alkene. Initial rates of hydroformylation with our catalyst were compared to the chloride analogue, [ClRh(IPr)(CO)2], and demonstrated the beneficial nature of replacing the halide with a carboxylate ligand, which is less inhibiting of the reaction. The synthesis of a bifunctional hydrogenation catalyst featuring a protic-NHC was attempted by addition of benzimidazoles to [Cl2Ru(diphosphine)]. Although these attempts were unsuccessful, a large number of complexes of the formula [Cl2Ru(diphosphine)(-N3-benzimidazole)2] were synthesized and proved to be effective catalysts for the chemoselective hydrogenation of ketones versus alkenes. Use of chiral diphosphines and 1-triphenylmethylbenzimidazole yielded catalysts capable of producing secondary alcohols with moderate enantioselectivity. / Thesis (Ph.D, Chemistry) -- Queen's University, 2010-09-17 12:44:52.686

No description available.

No description available.