N-Heterocyclic Carbene-metal Complexes Derived from Imidazolium-linked Cyclophane and Biimidazolium Salts

N-Heterocyclic Carbene-metal Complexes Derived from Imidazolium-linked Cyclophane and Biimidazolium Salts
Author: Valerie Jane Hesler
Publisher:
Total Pages:
Release: 2008
Genre: Carbenes (Methylene compounds)
ISBN:
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This thesis presents an investigation into the synthesis of metal complexes of (Nheterocyclic carbene)-based cyclophanes. There were three main areas of focus: synthesis and complexation of bis(4,5-dihydroimidazolium) salts; the synthesis and complexation of phenol-functionalised imidazolium cyclophanes; and the synthesis and complexation of (N-heterocyclic carbene)-based cyclophanes by C-C bond activation of biimidazolium salts with electron-rich metals. The synthesis of xylyl-linked bis(4,5-dihydroimidazolium) salts was investigated. Attempts to prepare these compounds by the cyclisation of a tetraamine (linear or macrocyclic) were unsuccessful due difficulties in preparing the tetraamines. The target compounds could be prepared by adapting the methods developed for the synthesis of bis(imidazolium) salts however problems associated with purification and stability of the products prevented complexation studies. A series of phenol-, phenoxide- and anisole-functionalised imidazolium cyclophanes were prepared. Their structural properties were investigated using dynamic nmr studies and X-ray crystallography. Complexation of the functionalised cyclophanes was investigated. The phenol cyclophane I formed a dinuclear complex with mercury(II). This complex is the first example of a complex derived from a phenol-functionalised imidazolium cyclophane. However the anisole cyclophane II and the unsymmetrical phenol/ortho cyclophane III were unable to form complexes possibly due to steric hindrance and instability of the cyclophane respectively. Preliminary complexation studies of the bis(imidazolium)phenol V suggested that complexation with palladium(II) and mercury(II) were possible but more work is required to determine the optimum reaction conditions. A series of biimidazolium salts VI (both new and known) were prepared. Previously reported biimidazolium salts have very low solubility in common solvents therefore the incorporation of long alkyl chains to the bridging group was investigated as a means to improve the solubility. The structure of the salts was explored using a range of techniques including dynamic nmr spectroscopy, cyclic voltammetry, UV/Visible spectroscopy, X-ray crystallography and mass spectrometry. Some of the biimidazolium salts were able to rotate about the C2-C2' bond and the free energy of activation for this process was estimated using dynamic nmr studies. C-C bond activation of the biimidazolium salts with palladium(0) was used to form a series of palladium(II) complexes (VII) of (NHC)-based cyclophanes. These reactions are the first examples of the synthesis of bis(NHC) complexes by C-C bond activation. The reactivity of the biimidazolium salts with palladium(0) was compared to their solution structure and it was found that only the biimidazolium that were able to rotate about the C2-C2' bond could react with palladium(0).

Silver(I) and Gold(I) N-heterocyclic Carbene Complexes

Silver(I) and Gold(I) N-heterocyclic Carbene Complexes
Author: Semih Durmus
Publisher:
Total Pages: 193
Release: 2006
Genre: Anti-infective agents
ISBN:
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"The introduction of N-heterocyclic carbenes (NHCs) to organometallic and inorganic chemistry was achieved by the synthesis and isolation of chromium and mercury NHC complexes by Öfele and Wanzlick in 1968. The synthesis and characterization of numerous carbene metal complexes by Lappert et al were a significant contribution to this area of chemistry. NHCs have become an important area of research after the isolation of the first stable carbene by Arduengo in 1991. In chapter 1, the synthesis and biological activities of NHCs and their silver(I) and gold(I) derivatives are discussed. In chapter 2, the synthesis and characterization of an imidazolium-linked cyclophane is discussed as well as its potential use as a medicinal agent. In chapter 3, the synthesis and characterization of a silver(I) NHC complex is reported. The antimicrobial activity of the silver(I) NHC complex is also reported against clinically important bacteria. In chapter 4, the synthesis of a variety of silver(I) NHC complexes and their carbene transfer reactions to gold(I) reagents are reported. The gold(I) NHC complexes are also investigated for their anticancer properties. In chapter 5, the use of urocanic acid as NHC precursor is reported. The synthesis and characterization of the first silver(I) NHC complex derived from biological molecule urocanic acid is discussed as well as its antimicrobial activity."--Abstract.

Amino Acid-derived Imidazolium Salts

Amino Acid-derived Imidazolium Salts
Author: Elliot Steeples
Publisher:
Total Pages: 0
Release: 2016
Genre:
ISBN:
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In the interest of producing functional catalysts from sustainable building-blocks, 1, 3-dicarboxylate imidazolium salts derived from amino acids were successfully modified to be suitable as N-Heterocyclic carbene (NHC) ligands within metal complexes. Complexes of Ag(I), Pd(II), and Ir(I) were successfully produced using known procedures using ligands derived from glycine, alanine, [beta]-alanine and phenylalanine. The complexes were characterized in solid state using X-Ray crystallography, which allowed for the steric and electronic comparison of these ligands to well-known NHC ligands within analogous metal complexes. The palladium complexes were tested as catalysts for aqueous-phase Suzuki-Miyaura cross-coupling. Water-solubility could be induced via ester hydrolysis of the N-bound groups in the presence of base. The mono-NHC-Pd complexes were seen to be highly active in the coupling of aryl bromides with phenylboronic acid; the active catalyst of which was determined to be mostly Pd(0) nanoparticles. Kinetic studies determined that...

The Medicinal Applications and Stability Evaluation of Silver(I) Carbene Complexes

The Medicinal Applications and Stability Evaluation of Silver(I) Carbene Complexes
Author: Khadijah M. Hindi
Publisher:
Total Pages: 271
Release: 2008
Genre: Carbenes (Methylene compounds)
ISBN:
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The formation of the first transition metal complexes of N-heterocyclic carbenes (NHCs) by Öfele and Wanzlick in 1968 and the discovery of the first stable and isolable free carbenes by Arduengo in 1991 fostered the growth of this fundamental area of chemical research. Currently, NHCs and their metal complexes are intensely studied for applications such as catalysis and most recently their pharmaceutical properties. The latter has shown promising results and thus will be the primary focus of this dissertation. In general, this dissertation will provide a description of the synthesis and antimicrobial properties of a novel class of silver NHC complexes derived from 4,5-dichloroimidazole and a comparison of its enhanced stability in relation to other silver NHCs synthesized in our laboratory. Chapter 1, the introduction, provides an overview of the medicinal applications of various metal NHC complexes including silver, gold, ruthenium, rhodium, and palladium. This follows a necessary discussion of the known properties of the metals including antimicrobial, antitumor, toxicity, resistance and proposed mechanisms of action. Chapter 2, discusses the synthesis, properties, and antimicrobial activity of a silver(I) acetate NHC complex derived from 4,5-dichloroimidazole with enhanced stability. This discussion is coupled with a comparison to two other structurally similar complexes lacking similar enhanced stability properties. Chapter 3 will provide a detailed account of the stability of the silver NHC complex reported in chapter 2 in various forms of aqueous media formulations including D2O, 0.9% NaCl/D2O, and broth/D2O mixtures utilizing NMR spectral techniques. Chapter 4 will focus on the synthesis of a silver NHC complex bearing a lipophilic substituent, its incorporation into L-tyrosine polyphosphate (LTP) nanospheres, and its in vivo antimicrobial efficacy when delivered to mice inoculated with Pseudomonas aeruginosa. Chapter 5 is devoted to the synthesis and characterization of imidazolium salt precursors functionalized with a variety of substituents and their corresponding silver NHC complexes. In chapter 6, the potential use of several different silver NHC complexes as a treatment of Onychomycosis, a common fungal infection of the nails is explored. The in vitro antifungal activity and penetration potential is reported.

Early Transition Metal Complexes of Carbene Donors Linked to Cyclopentadienyl Ring Analogues Or Amidine

Early Transition Metal Complexes of Carbene Donors Linked to Cyclopentadienyl Ring Analogues Or Amidine
Author: Susan Conde Guadano
Publisher:
Total Pages:
Release: 2010
Genre:
ISBN:
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The new indenyl-functionalised NHC potassium salt, 1-[3-(4,7-dimethylindenylpropyl)]-3- (2,6-diisopropylphenyl)imidazol-2-ylidenepotassium, has been synthesised. Complexes of titanium, zirconium and chromium containing this ligand and the two carbon bridge analogue, 1-[2-(4,7-dimethylindenyl)ethyl]-3-(2,6-diisopropylphenyl)imidazol-2 ylidene potassium, have been synthesised and characterised by X-ray crystallographic techniques. The following complexes were tested as catalysts for the oligomerisation of ethylene in the presence of MAO: 3-(2,6-diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidene(tertbutylimido) titanium chloride, 3-(2,6-diisopropylphenyl)-1-[3-(4,7- dimethylindenyl)propyl]imidazol-2-ylidene(tert-butylimido)titanium chloride, 3-(2,6- diisopropylphenyl)-1-[3-(4,7-dimethylindenyl)propyl]imidazol-2-ylidenezirconium trichloride, 3-(2,6-diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]imidazol-2- ylidenezirconium trichloride, 3-(2,6-Diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]- imidazol-2-ylidenechromium dichloride, 3-(2,6-diisopropylphenyl)-1-[3-(4,7- (dimethylindenyl))propyl]imidazol-2-ylidene chromium dichloride, 3-(2,6-diisopropylphenyl)- 1-[3-(4,7-dimethylindenyl)propyl]-imidazol-2-ylidene chromium methyl chloride and 3-(2,6- diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidenevanadium dichloride. The following alkyl chromium complexes containing 1-[2-(4,7-dimethylindenyl)ethyl]-3-(2,6- diisopropylphenyl)imidazol-2 ylidene potassium have also been synthesised: 3-(2,6- diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidene chromium phenyl chloride and 3-(2,6-diisopropyl-phenyl)-1-[2-(4, 7-dimethylindenyl)ethyl]-imidazol-2-ylidene chromium dibenzyl. Chromium cations have been synthesised using as starting materials the chromium alkyl complexes. The Cr(II) complex 3-(2,6-diisopropyl-phenyl)-1-[2-(4, 7- dimethylindenyl)ethyl]-imidazol-2-ylidene chromium monochloride and a partially oxidised dimerised product were also isolated. 5-(2-chloroethyl)- 1, 2, 3, 4-tetramethylcyclopentadiene and 5-(3-chloropropyl) 1, 2, 3, 4-tetramethylcyclopentadiene were synthesised and isolated as geminal isomers for the first time. The trialkyl chromium complex, tribenzyl chromium tris(tetrahydrofuran) was synthesised and also it was used as starting material for the complexes di(benzyl)chromium bis(1, 3- diisopropylimidazol-2-ylindene) and tri(benzyl)chromium TACN. All complexes were characterised by X-ray crystallography. The imidazolium salt 3-(2.6-diisopropylphenyl)-1-[N, N-bis(2,6- diisopropylphenyl)acetamidyl] imidazolium chloride was synthesised and used as a precursor for the synthesis of amidinate-functionalised NHC zirconium and amidine-functionalised NHC silver complexes. Double deprotonation of 3-(2,6-diisopropylphenyl)-1-[N, N'-bis(2,6- diisopropylphenyl)acetamidyl] imidazolium chloride gave the amidinate-functionalised NHC ligand, 3-(2.6-diisopropylphenyl)-1-[2-N, N'bis(2,6 diisopropylphenylamidinate)ethyl]imidazol-2-ylidenepotassium. Titanium, zirconium and chromium complexes containing this ligand were synthesised and characterised by X-ray crystallographic techniques. Transmetallation of the amidine-functionalised NHC silver complex with [Rh(COD)Cl]2 and [Ir(COD)Cl]2 gave the corresponding species. Rh(amidinefunctionalised NHC)(COD)Cl reacted with Na(BAr)4 (Ar = 3,5-CF3C6H3) to give the cation Rh(amidine-functionalised NHC)(COD)]+[BAr4]-. These species were also characterised by X-ray diffraction techniques.

Novel Imidazolium Salts, N-Heterocyclic Carbenes and Their Coordination Polymers

Novel Imidazolium Salts, N-Heterocyclic Carbenes and Their Coordination Polymers
Author: Ibrahim T. Siraj
Publisher:
Total Pages: 0
Release: 2012
Genre:
ISBN:
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N-heterocyclic carbenes (NHCs) have been developed in the last two decades as an important material in homogenous catalysis. Also MOFs have recently been receiving a great deal of attention due to their potential applications e.g. gas storage, adsorption and catalysis. This study involved the synthesis of new imidazolium salt functionalised with nitriles, carboxylates and pyridyl and their conversion into NHC complexes and porous coordination polymers. A series of nitrile substituted imidazolium salts were synthesised. 1,1-bis(4-cyanophenyl)-3,3-methylenediimidazolium and 1-bromomethyl-3-(4-cyanophenyl)imidazolium salts were synthesised by N-arylation and N-alkylation of 4-cyanophenyl imidazole. The bisimidazolium salt was used to synthesise a dimeric silver(I) NHC complex. Reaction of this silver complex with [Ru(p-cy)Cl2]2 results in transmetallation and the formation of the NHC complex [Ru(L)Cl]BF4. A platinum diNHC complex, [Pt(L)Br2], was synthesized by in situ deprotonation of the bisimidazolium salt precursor, using NaOAc and [Pt(COD)Cl2]. All were characterised crystallographically. Picolyl substituted imidazolium salts were synthesised, 1,3-bis(4-picolyl)imidazolium, 1,3-bis(2-picolyl)imidazolium and 1-(4-cyanophenyl)-3-(4-picolyl)imidazolium salt were synthesised using solvothermal synthesis and were characterised spectroscopically, by elemental analysis and X-ray crystallographic analysis. 1,3-bis(2-picolyl)imidazolium chloride was prepared according to literature method while the 1-methyl-3-(4-picolyl)imidazolium salt was synthesised from the methyl imidazole and 4-picolyl chloride. All the picolyl substituted imidazolium salts were converted to Ag(I) NHC complexes of the type [Ag(NHC2]+. The bis 4-picolyl imidazolium was used to synthesise two isostructural highly porous coordination polymers of Ag(I) and Cu(I). New carboxylate imidazolium salts, 3,3'-methylenebis(1-(4-carboxyphenyl)-1H-imidazol-3-ium), 1,3-bis(4-carboxyphenyl)-1H-imidazol-3-ium, 1,3-bis(3-carboxyphenyl)-1H-imidazol-3-ium, 3-(4-carboxyphenyl)-1-methyl-1H-imidazol-3-ium and 1-benzyl-3-(4-carboxyphenyl)-1H-imidazol-3-ium salts were prepared from hydrolysis of the corresponding nitrile imidazolium salts in HX (X = Br, Cl). The 1-benzyl-3-(4-carboxyphenyl)-1H-imidazol-3-ium imidazolium salt formed a rhodium diNHC complex [Rh(L)2Br(CO)] by reacting the ligand with rhodium acetate in a solvothermal process. The 1,3-bis(4-carboxyphenyl)imidazolium salt reacted with LnCl3.XH2O in DMF under a solvothermal process to give two isostructural MOFs of La(III) and Ce(III).