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Ring-walking, metal coordination and aryl-halide oxidative addition (ringwalk)
Start date: 28 Sep 2008, End date: 27 Sep 2010 PROJECT  FINISHED 

The proposed project deals with the formation of new late transition metal-based stilbene and stilbazole complexes, formed via a series of transformations, including metal-olefin coordination, metal ring-walking, and aryl-halide oxidative addition. This project is related to recently published results (van der Boom, M. E. et al J. Am. Chem. Soc. 2005, 127, 9322; Organometallics, 2006, 25, 3308; Organometallics, 2007, in press; Chem. & Eng. News 2005 Sept. 19,). Our studies indicate that a zerovalent platinum center coordinates to the stilbene carbon-carbon double bond and subsequently walks in the solid state and in solution over the π-system of the stilbene ligand prior to activation of an aryl– halide moiety. The cleavage of the aryl–halide bond is the rate determining step. This model system is an ideal vehicle to observe several organometallic steps in a consecutive manner. We are interested in studying the mechanistic aspects of these reactions, especially the metal ring-walking process. Many challenging questions remain. For example, is it possible by proper ligand design to direct a metal center to a specific molecular site? The proposed research will be conducted by varying the nature of the metal complex precursors (e.g., metal periodic table position, oxidation state, phosphine vs nitrogen ligands, chelating vs non-chelating ligands, …) and by preparation of stilbene and stilbazole ligands. Kinetic studies will be carried out using (variable temp.) NMR and UV/vis spectroscopy. Some of the compounds will be used for crystal engineering (van der Boom et al , M. E. Crys. Growth & Des. 2005, 5, 1671), and coordination-based assembly of intrinsically acentric multilayers (van der Boom, M. E. et al J. Am. Chem. Soc. 2006, 128, 7374). The acquired mechanistic information may be used for the design of new metal-mediated organic reactions and homogeneous catalysis, including arene functionalization, activation of aryl–halides, and cross-coupling reactions.
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