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Triazine based N-Heterocyclic carbenes - synthesis, coordination and catalysis

Hasson, Mohammed 2015. Triazine based N-Heterocyclic carbenes - synthesis, coordination and catalysis. PhD Thesis, Cardiff University.
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This thesis describes the synthesis and characterization (1H, 13C NMR, CHN, and X-ray) of new NHC ligands incorporating a triazine core and their complexation with Ag(I), Pd(II) and Ru(II) metals. Imidazolium salts [2.4H]I – [2.7H]Br and [2.10H] - [2.15H]Br were obtained by reaction of 2,4-diamino-6-chloro-1,3,5-triazine (diamino = morpholine, piperidine, diethylamine, or dimethylamine) with H- imidazole followed by alkylation with a variety of alkyl halides such as propyl, butyl, octyl bromides or isopropyl iodide. While the imidazolium salts [2.3H]Cl, [2.8H]Cl, [2.9H]Cl and [2.13H]Cl were prepared by reaction of N-substituent imidazole (mesityl, phenyl ethyl, and methyl) with 2,4-diamino-6-chloro-1,3,5-triazine (diamino = morpholine or dimethylamine). Silver complexes were prepared from the reaction of Ag2O with an NHC precursor salt using in situ deprotonation techniques giving the desired structures in good yield. X-ray studies with other spectral and analytical studies reveal the formation monodentate complexes of the NHC ligands. The coordination geometry at Ag is slightly distorted from the idealised linear geometry. The Ag(I)-NHC complexes were used as NHC transfer reagents to prepare Ru(ІІ) and Pd(ІІ) complexes. New monodentate Pd (ІІ) complexes were prepared by in situ deprotonation of the NHC ligand by K2CO3 in the presence of PdCl2. The catalytic activity of the complexes in the Suzuki reaction was explored with conversions of up to 100 % being observed. Bis(carbene)Pd(ІІ) complexes were prepared by transmetalation from the silver complexes with Pd(MeCN)Cl2. X-ray crystallography shows a distorted square planar geometry around the palladium metal centre for both complex types. A series of Ru (ІІ) complexes were prepared by transmetalation techniques using the silver complexes as transfer reagents with [Ru(η6-arene)Cl2]2 in dichloromethane. Single crystal studies along with other spectral and analytical studies reveal the coordination of the triazine-NHC ligand in a chelating mode where both the carbene and one of the N-donors of the triazine group ligate the metal. The complexes are active for the transfer hydrogenation of ketones with conversions up to 96%.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Oct 2016 03:33

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