Dianionic Janus-Type N-Heterocyclic Carbenes and their Zwitterionic Gold and Silver Metal Complexes
While early efforts have been made to explore the chemistry of neutral multitopic nonchelating N-heterocyclic carbenes (NHCs), limited progress has been made in the development of anionic counterparts. This thesis describes the synthesis and characterization of two new dianionic bis(maloNHC). The corresponding thiones were generated by the reaction of the free carbenes with an excess of sulfur. The utility of these extended biscarbenes for the construction of homobimetallic systems has been demonstrated by direct coordination to two coinage metals. The resulting zwitterionic metal complexes of type [(Ph3P)M(NHC)M(PPh3)] (M = Au, Ag) have been fully characterized by spectroscopic techniques and X-ray crystallography. One of the new ligands positions the two metal centers at a distance of 24.2 Å, to our knowledge the longest distance reported so far for a Janus-type bis(NHC) ligand. A library of bridging NHC ligands of various sizes and shapes is essential for the synthesis of new supramolecular hosts of controlled size and shapes. The unique topological properties of these systems create the potential for them to serve as building blocks for the preparation of novel metal-organic frameworks such as supramolecular cages and organometallic polymers, systems not accessible with the current arsenal of neutral Janus-type bis(NHC)s.
carbene, N-heterocyclic, Janus, anionic, bridging, Chemistry
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