| Summary: | This thesis describes the design, synthesis and study of metal derivatives of new acyclic
and macrocyclic ligands containing pyridine and amide groups.
Chapter 1 provides an overview of metal-carboxamide and pyridinamide chemistry
including a number of important pincer compounds, macrocyclic involvement in
formation of metal-templated rotaxanes and catenanes, oxidation catalysts, anion
receptors and bimetallic complexes.
Chapter 2 discusses new palladium(II) complexes of an acyclic ligand bearing pendant
2-pyridyl-6-methyl arms, N,N_-bis(6-methyl-2-pyridinyl)-2,6-pyridinedicarboxamide
(H2LMe). H2LMe formed a dimer [Pd(LMe)]2 when treated with palladium(II) salts and
non-ligating bases, but in the presence of DBU the palladium-DBU adduct,
Pd(LMe)(DBU), was formed. Reaction of Pd(LMe)(DBU) with methyl iodide resulted in
the displacement of the DBU ligand and the concomitant formation of cationic
monomeric complex, [PdI(LMe{Me}2)]I and dimeric N-methylpyridinium complex,
[Pd(LMe{Me})]2I2. A series of ligands, N,N_-bis(x-tolyl)-2,6-pyridinedicarboxamide (x
= 2, 3, 4) (H2Lxtol), bearing ortho-, meta- and para-tolyl groups, was prepared and these
were coordinated to palladium(II) in their deprotonated form so that the effect of the
pendant pyridine rings and steric environment around the metal on the reactivity of
metal derivatives could be investigated. Stable palladium(II) derivatives of the
deprotonated H2Lxtol ligands, Pd(Lxtol)(E) (E = DBU, n-butylamine, p-tolylisocyanide)
were prepared. The p-tolylisocyanide adducts reacted with pyrrolidine or p-toluidine to
afford the stable bis(amino)carbene complexes, Pd(Lxtol)(=C(NH-p-tolyl)(pyrl)) and
Pd(Lxtol)(=C(NH-p-tolyl)2), respectively. The coordinated DBU ligands in
Pd(Lxtol)(DBU) and Pd(LMe)(DBU) were displaced by n-butylamine to afford the
corresponding n-butylamine adducts, and their relative rates of exchange were
determined by 1H NMR spectroscopy.
Chapter 3 discusses palladium(II) complexes of dicationic N-methylpyridinium ligands
prepared by treating H2LMe or the series of ligands, N,N_-bis(x-pyridinyl)-2,6-
pyridinedicarboxamide (x = 2, 3, 4) (H2Lxpy) that contain pendant 2-, 3-, or 4-pyridyl
groups, with methyl triflate to form [H2LMe{Me}2][OTf]2 or [H2Lxpy{Me}2][OTf]2,
respectively. These ligands were coordinated in their deprotonated forms to
palladium(II) to give [PdCl(Lxpy{Me}2)]OTf. The chloro ligands in these metallated
complexes were displaced on treatment with silver triflate in acetonitrile or water to
afford the corresponding solvent adducts. The coordinated solvent molecules in
[Pd(LMe{Me}2)(NCCH3)][OTf]2 and [Pd(Lopy{Me}2)(OH2)][OTf]2 could in turn be
displaced by p-tolylisocyanide to form isocyanide adducts, [Pd(LMe{Me}2)(CN-ptolyl)][
OTf]2 and [Pd(Lopy{Me}2)(CN-p-tolyl)][OTf]2. Dicationic bis(amino)carbene
complexes [Pd(LMe{Me}2)(=C(NH-p-tolyl)2)][OTf]2 and [Pd(Lopy{Me}2)(=C(NH-ptolyl)
2)][OTf]2 were prepared by treating the corresponding isocyanide precursors with
p-toluidine. A 1H NMR spectroscopic study was performed to compare the relative
rates of reaction of p-toluidine with the neutral tolyl isocyanide complexes
Pd(Lxtol)(CN-p-tolyl) and the dicationic isocyanide complexes [Pd(LMe{Me}2)(CN-ptolyl)][
OTf]2 and [Pd(Lopy{Me}2)(CN-p-tolyl)][OTf]2 to determine the influence of the
steric and electronic environments on the reactivity of the isocyanide ligand. On
deprotonation of the amide groups in [H2LMe{Me}2][OTf]2 and [H2Lopy{Me}2][OTf]2
the neutral free bis(imine) compounds LMe{Me}2 and Lopy{Me}2 could be isolated.
Chapter 4 discusses extended acyclic ligands H4LpdnA and H4LSpyA (H4LxA) that were
derived from the precursor N,N_-bis(6-acrylamido-2-pyridinyl)pyridine-2,6-
dicarboxamide (H4LacrA) through Michael addition of pyrrolidine or 2-
mercaptopyridine, respectively, to the acrylyl groups. The double-helical dimers
[M(H2LxA)]2 were formed when these ligands were treated with palladium(II) or
mercury(II) acetate, and in the presence of DBU the adducts Pd(H2LxA)(DBU) were
formed. In the absence of added base, palladium(II) acetate coordinated between the
tail amine groups of the ligand H4LpdnA which bears terminal pyrrolidyl groups.
Chapter 5 discusses complexes of macrocycles formed from double Michael-type
addition of the amines n-butylamine, 2-(aminomethyl)pyridine, 2-(aminoethyl)pyridine,
N,N-dimethylethylenediamine and N,N_-bis(2-pyridylmethyl)ethylenediamine to the
pendant acrylyl groups of H4LacrA. The macrocycle synthesised from addition of nbutylamine,
H4LnBu, reacted with palladium(II) acetate and DBU to form a complex in
which palladium was coordinated in the macrocycle headgroup and an aminolactam
resulting from hydrolysis of DBU was coordinated on the fourth site of the metal,
Pd(H2LnBu)(NH2Lac[7]). A palladium derivative of H4LnBu with a labile water ligand,
Pd(H2LnBu)(OH2), was prepared and used for subsequent syntheses of n-butylamine,
DBU and p-tolylisocyanide adducts. When treated with p-toluidine, the isocyanide
ligand of the macrocyclic p-tolylisocyanide adduct was displaced to form a p-toluidine
adduct. Modified macrocycles with other amine donors incorporated into the tail were
prepared in order to provide an additional site for metal complexation. The macrocycle
with an additional N,N-dimethylamino group, H4Ldmen, reacted with metal salts to form
complexes where metallation had taken place at the tail amide groups and the tail amine
group interacted with the metal.
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