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Synthesis and applications of poly N-heterocyclic carbenes and investigation of aldimine couplingPowell, Adam Bradley 17 December 2012 (has links)
The design, synthesis, characterization and application of carbene-based
metallopolymers are described herein. Metallopolymers have found wide applications in the fields of photovoltaics, energy storage and electrochromic windows. The incorporation of N-heterocyclic carbene (NHC) functionalities into a polymerizable scaffold would allow for many different metals to be attached in a facile and high-yielding manner. Such complexes could be functionalized onto surfaces and utilized as
either spectroscopic or antimicrobial devices.
Early attempts in our lab focused on utilizing bis(thiophene) diimines (instead of NHCs) as scaffolds for metal chelation and polymerization. This approach was
unsuccessful due to the lability of the diimine moiety under electrochemical cycling and
the thiophene moieties were not able to undergo polymerization. In order to more fully understand the key transformation in synthesizing the thiophene-substituted diimines, a comprehensive investigation of the aldimine coupling transformation was undertaken. A high concentration of substrate and catalyst was determined to be the most important
factor in obtaining high yields of the dimerized products. Green solvents such as acetonitrile and hexanes could be used for the dimerization reaction when the cyanide counteranion was changed from sodium to tetrabutylammonium. The steric limitations were systematically identified and a series of possible substrates have been ruled out as
viable candidates for dimerization.
Applying the experience gleaned from earlier reports, the first example of an NHC polymer was prepared in which the monomer features an NHC functional group
orthogonally connected to its main chain. A polymerizable imidazolylidene-AuCl complex containing pendant bithiophene moieties was prepared by a high yielding, multistep procedure. Oxidative electropolymerization of this monomer afforded the desired
polymer (Au[NHC]Cl)n, which was characterized on the basis of electrochemical studies as well as by X-ray crystallography, photoelectron and UV-vis spectroscopy.
The methodology described above was expanded to develop a series of analogous poly(N-heterocyclic carbene) complexes with appended entities (M = Ir, Au, Ag, or S)and found to be electrochromic. Most of the polymers exhibit an intense absorbance wave at 700 nm under oxidative conditions which is attributable to the formation of polaron excitations along the polymer main chain. The presence of a transition metal significantly
increased the electrochromic character of the polycarbene system. The iridium-containing
polymer was found to possess significant near-infrared (NIR) absorbance at 1100 nm in which the metal moiety effectively functions as an electron sink. Electrochemical analysis of the polymer thin films revealed that they exhibit highly reversible
electrochromic activities. / text
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Cyanide-catalyzed C-C bond formation: synthesis of novel compounds, materials and ligands for homogeneous catalysisReich, Blair Jesse Ellyn 25 April 2007 (has links)
Cyanide-catalyzed aldimine coupling was employed to synthesize compounds
with 1,2-ene-diamine and ñ-imine-amine structural motifs: 1,2,N,N'-
tetraphenyletheylene-1,2-diamine (13) and (+/-)-2,3-di-(2-hydroxyphenyl)-1,2-
dihydroquinoxaline (17), respectively. Single crystal X-ray diffraction provided solidstate
structures and density functional theory calculations were used to probe isomeric
preferences within this and the related hydroxy-ketone/ene-diol system. The enediamine
and imine-amine core structures were calculated to be essentially identical in
energy. However, additional effects-such as ÃÂ conjugation-in 13 render an enediamine
structure that is slightly more stable than the imine-amine tautomer (14). In
contrast, the intramolecular hydrogen bonding present in 17 significantly favors the
imine-amine isomer over the ene-diamine tautomer (18).
Aldimine coupling (AIC) is the nitrogen analogue of the benzoin condensation
and has been applied to dialdimines, providing the first examples of cyclizations effected
by cyanide-catalyzed AIC. Sodium cyanide promoted the facile, intramolecular
cyclization of several dialdimines in N,N-dimethylformamide, methanol, or
dichloromethane/water (phase-transfer conditions) yielding a variety of six-membered
heterocycles. Under aerobic conditions, an oxidative cyclization occurs to provide the
diimine heterocycle.
Cyanide-catalyzed aldimine coupling was employed as a new synthetic method
for oligomerization. Nine rigidly spaced dialdimines were oxidatively coupled under
aerobic conditions to yield conjugated oligoketimines and polyketimines with
unprecedented structure and molecular weight (DP = 2 - 23, ~700 -8200 g/mol). The ñ- diimine linkage was established based on IR spectroscopy, NMR spectroscopy, size
exclusion chromatography, and X-ray crystallographic characterization of the model
oxidized dimer of N-benzylidene-(p-phenoxy)-aniline. Cyclic voltammetry indicates ptype
electrical conductivity, suggesting they are promising candidates for plastic
electronic devices.
The cyanide-catalyzed benzoin condensation reaction of 4-substituted
benzaldehydes followed by oxidation to the diketone, and the Schiff Base condensation
of two equivalents of o-aminophenol provides 2,3-(4-X-phenyl)2-1,4-(2-
hydroxyphenyl)2-1,4-diazabutadiene. The ligand is given the moniker X-dabphol.
These ligands are readily metallated to form M-X-dabphol complexes. The copper
complexes catalytically fix CO2 with propylene oxide to yield propylene carbonate. DFT
studies along with a comparison with Hammet parameters help validate and elaborate on
the catalytic cycle and the catalytic results obtained. The nickel complex is competent
for olefin epoxidation. Synthesis, characterization, X-ray structure, DFT analysis, and
catalytic activity of the parent nickel dabphol complex are reported.
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