Coordination Complexes of New Acyclic and Macrocyclic Ligands
Abstract (Summary)Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. Macrocyclic coordination chemistry is a huge field, and this thesis specifically deals with the design and synthesis of a series of acyclic and macrocyclic ligands containing pyridine and amide groups. Metal complexes of these ligands as well as host-guest interactions involving the free or metallated ligands have been studied. The new ligands feature a bis-amide-pyridine headgroup that can. on deprotonation, coordinate a metal ion, and pendant pyridine groups that are specifically directed towards the coordination site trans to the headgroup pyridine, so that they may interact with a group coordinated there. Chapter one primarily illustrates some complexes reported in the literature as a background to the work undertaken in this thesis, with a specific emphasis on examples with applications in areas such as biology or catalysis. This review covers acyclic mono- and polymetallic complexes, mono- and polymetallic macrocyclic complexes, synthetic methods and some examples of anion receptors and host-guest complexes. This is followed with a discussion on the design of the ligands that form the basis of this work, focussing on the pyridine and amide functional groups. A brief review of some results previously obtained in this area is then presented. In chapter two some complexes of the acyclic ligand designated H2 LMe are investigated. This ligand has methyl groups attached to the pendant pyridine groups. Palladium and nickel formed the dimeric complexes, [PdLMe]2 and [NiLMe]2, where the metal coordinates to the headgroup of one ligand and to a pendant pyridine of the other half of the dimer, and these were both structurally characterised. A mixed palladium-nickel complex [PdLMe][NiLMe]was also synthesised, as well as a platinum complex, [Pt2LMe(PhCN)], that was not dimeric but which contained two platinum centres within the ligand cavity. The nickel dimer could be oxidised to give a Ni(III)/Ni(III) species. An anionic iron complex with two deprotonated ligands coordinated around the metal centre was synthesised and structurally characterised as [Et4N][Fe(LMe)2]. A cobalt complex. CoCl(LMe)bipy, was also synthesised and structurally characterised. An analogue of H2LMe that has pendant tolyl groups and is designated H2LMe* was synthesised, to study the influence of the pendant pyridine groups by comparative studies with H2LMe. The synthesis and coordination chemistry of this ligand is described in chapter three. Monomeric nickel and platinum products could be isolated but only as isocyanide complexes [Ni(LMe*)CNp-tolyl] and [Pt(LMe*)CNp-tolyl], whilst the palladium complex could be isolated as an acetonitrile adduct, [Pd(LMe*).MeCN]. This reacted further to give isocyanide, carbene and phosphine complexes. Of note, the ethoxy- and tbutylaminocarbenes [Pd(LMe*)c(OEt)NH(p-tolyl)] and [Pd(LMe*)C(NHtBu))NH(p-tolyl)] were very stable and coordination of triethylphosphine to the palladium centre to give [Pd(LMe*)PEt3] showed that this bulky ligand could be accommodated between the pendant tolyl groups. Methylation of the isocyanide complex at one of the amidate oxygens resulted in the formation of a cationic species. Cobalt and iron complexes were also synthesised and the iron complex was structurally characterised as [HDBU][Fe(LMe*)2]. The synthesis of a ligand (designated H2LNH2) that is analogous to H2LMe but with amino groups in place of the methyl group allows larger ligands with four amide groups to be formed, and these derivatives are described in chapter four. The ligands designated H4LprA and H4LpvA were synthesised by reaction of H2LNH2 with propionoyl or pivaloyl chloride, respectively. A crystal structure of H4LPVA showed the ligand has a U-shaped conformation in the solid state. Metal complexes were formed with these two ligands. These included a complex of palladium, which appeared to have the same dimeric structure as [PdLMe]2, a mercury derivative, which appeared to form an oligo-or polymeric product, and nickel and copper derivatives which also appeared to form polymetallic species. The interaction of barbital with H4LPVA was studied by proton NMR and evidence of a hydrogen-bonding interaction was obtained. A related tetraamide extended ligand with ferrocenyl groups was synthesised by the reaction of Fc(cocl) with H2LNH2 and is the subject of chapter five. This ligand, H4LFCA was structurally characterised and had a similar structure to H4LPVA. Metal complexes were again synthesised, and anion recognition and host-guest interactions involving both the free ligand and the metal complexes were studied by NMR and electrochemistry. A related extended ligand with terminal vinyl groups was synthesised through the reaction of H2LNH2 with acryloyl chloride and this was designated H4LacrA. Macrocycles were formed by double Michael addition of amines to the vinyl groups of this ligand. In particular, reaction with nbutylamine gave the macrocycle H4LnBu, and reaction with ethylenediamine gave H4Len in high yield. Cobalt complexes of both these macrocycles and the acyclic precursor, H4LacrA, were studied. The complex formed with the acyclic ligand appeared to contain two ligands coordinated to the cobalt centre via the pendant rather than the headgroup amides, resulting in a square-planar coordination geometry around the cobalt centre. Attempts were made to close the two acyclic ligands and form a catenate. palladium formed different complexes with the macrocycles H4LnBu, and H4Len depending on the strength of the base added during the reaction. Absence of base during the metallation reaction led to formation of a complex [PdCl2H4Len] in which the PdCl2 moiety was coordinated to the amine groups of H4Len. The presence of sodium acetate resulted in the complexes [PdClH3LnBu] and [PdClH3Len] where the palladium coordinated to one of the amidates at the aliphatic end of the ligand. The H4LnBu complex was structurally characterised. Addition of DBU to the metallation reactions resulted in coordination of two amidate groups to palladium. Bimetallic complexes [Pd2LnBu] and [Pd2Len] were also found. Copper and nickel formed hexametallic dimeric complexes with the two macrocycles H4LnBu and H4Len, and in particular the crystal structure of the minor hydrolysis product obtained from the reaction of CuCl2 with H4Len gave the complex [Cu2O(LNH2)CuCl2.EtOH]2.
School Location:New Zealand
Source Type:Master's Thesis
Date of Publication:01/01/1998