Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Brian L. Pagenkopf. Vita. Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Klaus H. Theopold, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Th.--Sci. phys.--Lille 1, 1979. N°: 440. / Extr. en partie de Biochimie, 57, 1975,401-415.

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This thesis presents investigations related to interactions of chelating ligands (macrocyclic and acyclic) with neutral and ionic species in solution. Following a brief introduction on coordination chemistry, each topic is presented separately in three chapters. In Chapter I, thermodynamic studies on drug cyclodextrin interactions in water and in chloroform at 298.15 K are discussed in relation to the effect of the macrocycle on the transfer of N1-substituted sulphonamides from water to chloroform. It is concluded that the transfer of the drug in this solvent system is thermodynamically more favoured in the absence than in the presence of cyclodextrin. Chapter II concerns thermodynamic aspects on calixarenes and their ester derivatives. As far as calixarenes are concerned, thermodynamic parameters of complexation of tert-butylamine and p-tert-butylcalix[4]arene in benzonitrile suggest that two processes are involved; the formation of the adduct followed by that of an endo-calix complex. The interaction of alkyl-p-tert-butylcalix[4]arene tetraethanoates with alkali-metal cations in acetonitrile and in benzonitrile at 298.15 K was studied by titration calorimetry. The limitation of this technique to derive stability constant data for highly stable complexes led to the development of a double competitive potentiometric method. Thermodynamic data are discussed in terms of the solvation of host, guest and resulting complex in these solvents. Chapter III discusses synthesis, characterisation and acid-base properties of ethylenedinitrilo-N,N1-diacetic-N,N1-bis(1-phenylethylacetamido) acid (edtamba) and ethylenedinitrilo-N,N1-diacetic-N,N'bis(pyridylacetamidoacetamioe)acid (edtapa) This is followed by the thermodynamics of complexation of these ligands with metal cations (Pb(II), Cd(II), Cu(II), Ni(II), Zn(II) and Co(II) in water at 298.15 K. These results show that unlike EDTA, edtamba and edtapa do not interact selectively with these cations as a result of a remarkable enthalpy-entropy compensation effect. Computer programs written during the course of these investigations are appended.

The development of abundant and economical first-row transition metal-based catalysts is an appealing area of research for efficient and selective chemical transformations. In this context, iron complexes are highly desirable as they feature a range of accessible oxidation states allowing for transfer of one or two electrons to or from a substrate. Therefore, over the past two decades, many iron-based catalysts have been developed, extensively studied, and exploited for catalysis ranging from oxidation and reduction to C-C bond forming reactions. In homogeneous transition metal catalysis, the ligand plays a vital role in determining activity and selectivity of the above stated catalytic reactions. Some key features of ligands that support both stoichiometric and catalytic reactions of metal complexes include: 1) strong chelation ability to metals, 2) tunability of donor atoms, 3) strong field ligands such as phosphine, phosphite, CO, and hydride favoring low-spin complexes, 4) hemilability allowing substrate activation via reversible dissociation of one donor atom, and 5) redox-activity enabling donation or accepting of electrons, thus avoiding a change of metal oxidation state. To this end, bifunctional ligands containing the above described properties have emerged as important elements in chemical synthesis and in catalysis. Iron and other transition metal complexes containing multidentate bifunctional ligands have recently been shown to activate small molecules and catalyze a number of chemical transformations with activity and selectivity typical of more well-studied precious metals. The objective of this thesis is to further advance the field of bifunctional ligands by preparing new sterically svelte tridentate ligands with a mixture of hard nitrogen and soft sulfur donors and to investigate their iron chemistry. The overall goal is to then explore the utility of these iron complexes as potential bifunctional catalysts. Chapter 2 describes a one-step synthesis of a new SMeNHS ligand in excellent yield that undergoes ring-opening on treatment with Fe(OTf)2 affording a thiolate-bridged, trinuclear iron complex, [Fe3(µ2-SMeNS−)4](OTf)2. The structure, spectroscopic, magnetic, and computational studies of this iron complex are provided along with its solvent-dependent reactivity towards monodentate donor ligands that yields both dinuclear and mononuclear derivatives. Chapter 3 describes the formation of an electron-rich Fe(II) thiolate complex, [Fe(SMeNS)(PMe3)3](OTf) and its substitution reactivity with both mono- and bidentate donor ligands. On heating this complex, an oxidative thioether Caryl-S bond cleavage is observed, leading to a cationic Fe(III)-CNS thiolate analog. Reduction of this Fe(III) species with cobaltocene yielded a neutral Fe(II)-CNS thiolate complex. To investigate the bifunctional activity of these Fe(II) complexes, both Fe(II)-SNS and -CNS species were assessed as precatalysts for amine-borane dehydrogenation. Chapter 4 employs the SMeNHS ligand in formation of a neutral, imine-coupled Fe-N2S2 complex that serves as an efficient and selective aldehyde hydroboration catalyst using pinacolborane. A reaction profile kinetic analysis implicates the hemilability and redox-active properties of this complex. Chapter 5 introduces the new unsymmetrical amine ligand, SMeNHSMe, and details its iron chemistry with formation of a pseudooctahedral Fe(II) bis(amido) complex. The Mössbauer spectra, MCD study, and DFT calculations support formation of a minor five-coordinate isomer in solution due to the hemilability of the six-membered ring thioether group. Reactivity studies of this Fe(II) species with a variety of donor ligands confirmed this lability and protonation at nitrogen yielded a cationic Fe(II) amine-amido complex. Reaction of the latter with the tridentate phosphine, triphos, gave a 16e-, low-spin, square-pyramidal Fe(II) complex that proved to be a robust precatalyst that is more active for dehydrogenation of dimethylamine-borane vs. ammonia-borane. Formation of a monohydride catalyst resting state under these reaction conditions is suggestive of a bifunctional activation pathway. Finally, Chapter 6 concludes the outcomes of the iron chemistry of hemilabile SNS ligands and discusses future directions and opportunities to extend these ligand systems to other transition metals. The knowledge gained by the stoichiometric and catalytic reactivity of iron-SNS complexes presented herein contributes to our understanding of bifunctional catalysis. With the increasing demand for base metal catalysts in chemical industry for efficient and selective synthesis of value-added chemicals, iron SNS complexes could offer economical, active, and selective catalyst precursors.

This thesis contains the preparation of a new design of ligand for the palladium catalysed allylic substitution reaction. The phosphine oxazoline ligands detailed in the thesis give high levels of enantiocontrol when used in conjunction with symmetrical allyl systems in the palladium catalysed allylic substitution reaction. For unsymmetrical allyl systems the palladium catalysed allylic substitution process proceeds with complete regiocontrol and high levels of stereocontrol are again observed. The products from the palladium catalysed allylic substitution reaction can be readily converted to succinic acids, γ-lactones and aryl propanoic acids.

The condensation reaction of iPr2PCl with hexamethyldisilazane, HN(SiMe3)2, followed by oxidation with sulfur, selenium or hydrogen peroxide yields Pr2P(E)NHP(E'),iPr2, where E = S, Se or 0. Single crystal X-ray experiments give a hydrogen bonded chain in all cases. Analogous PhO, EtO, Et and Ph substituted compounds were synthesised via condensation reactions between R2P(S)NH2 and R'P(S)CI yielding R2P(S)NHP(S)R'2 (R =PhO, Ph; R' = iPr, Et, EtO). Further crystallographic studies revealed iPr2P(S)NHP(S)(OPh)2 and Et2P(S)NHP(S)Ph2 to be hydrogen bonded dimers and iPr2P(S)NHP(S)Ph2 and Et2P(S)NHP(S)(OPh)2 to be hydrogen bonded chains. Reacting these compounds with Zn, Cd, Pd and Pt chlorides led to the formation of tetrahedral and square planar coordination complexes. Crystallographic studies on the complexes of R2P(E)NHP(E')R'2 revealed surprising ME2P2N ring geometries, some adopting pseudo "boat" conformations and others adopting pseudo "chair" conformation. Reactions of R2P(S)NHP(S)R'2 with CuC12 yielded trimeric copper(I) complexes of the type CU3[R2P(S)NP(S)R' 2]3. The trimeric system was found to be fluxional in solution. Crystallographic studies on the complexes show the trimer to have CU3S3 core. Further reactions of R2P(S)NHP(S)R' 2 with various tellurium (H) and (IV) salts yielded complexes of the types Te[R2P(S)NP(S)R' 2]2 and Te[R2P(S)NP(S)R' 2]Cl2,C6H4.0CH3. Crystallographic studies on the complexes show the tellurium to adopt pseudo two coordinate, four coordinate (square planar) and five coordinate (square based pyramid) arrangements. Tetradentate ligands of the type R2P(S)NHP(S)Ph(CH2)3P(S)PhNHP(S)R2 (where R = Ph or OPh) were synthesised by the condensation of NH2P(S)Ph(CH2)3P(S)PhNH2 with R2P(S)CI. Preliminary coordination studies suggest the formation of ML complexes were M = Zn, Cd and Ni. Molecular modelling techniques were used to investigate the optimum size of the "spacer groups" which links the two dithioimidophosphinate ligands. Using MNDOd and DFT optimisations, and with comparison to unlinked examples, the size of the ideal group was determined with respect to each particular metal.