Silver, mercury and ruthenium complexes of N-heterocyclic carbene linked cyclophanes

Rosenani S M Anwarul Haque

Research output: ThesisDoctoral Thesis

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This thesis describes the synthesis and isolation of silver, mercury, ruthenium and palladium complexes of bidentate N-heterocyclic carbenes (NHCs), derived from imidazolium-linked cyclophanes and related bis-imidazolium salts. The cyclophane structures contain two imidazolyl links between ortho- and meta- substituted aromatic rings and the related structures are ortho-, meta- and para-xylyl linked bis-imidazolium salts. The complexes have been characterised by NMR spectroscopy and X-ray crystallography. The synthesis of five new silver complexes has been achieved via a simple complexation reaction of the cyclophane and bis-imidazolium salts with the basic metal source Ag2O. The new silver carbene systems are thermally stable. Three of the complexes are dinuclear, cationic complexes, while two are mononuclear complexes, one cationic and one neutral. A number of mono- and di-nuclear mercury(II)-NHC complexes have been synthesised from the ortho- and meta-linked cyclophanes and the related meta-linked bis-imidazolium salts. The mercury complexes were prepared by direct mercuration method using mercury(II) acetate. The syntheses were perfomed in air and the complexes are stable to air and moisture. Mercury complexes I and II represent the first example of mononuclear metal complexes derived from meta-substituted imidazolium-linked cyclophanes. NHC-ligand transfer reactions from NHC-silver complexes and NHC-mercury complexes are described. An ortho-cyclophane ligand was successfully transfered from a silver complex to its palladium counterpart. Furthermore, palladium complex III, bearing a para-xylyl linked bis-NHC ligand, was made by transmetallation from both a silver and mercury complex. This is the first reported NHC-palladium complex of a para-xylyl linked bis-NHC ligand. A new redox transmetallation method for NHC ligand transfer, using a mercury complex, is presented. A palladium complex was made via redox transmetallation using a mercury complex of an ortho-NHC-cyclophane. A ruthenium(II)-NHC complex, IV containing an ortho-cyclophane ligand has been prepared via silver transmetallation and in situ complexation methods. In the transmetallation route, a silver complex of an ortho-cyclophane was treated with RuCl2(PPh3)3 to form IV. This complex represents the first example of a ruthenium complex bearing an NHC-cyclophane ligand, v and is also the first example of a metal complex derived from an imidazolium-linked cyclophane where the arene unit of the cyclophane is also involved in bonding to the metal centre.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2007


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