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Ring-walking, metal coordination and aryl-halide oxidative addition

Final Report Summary - RINGWALK (Ring-walking, metal coordination and aryl-halide oxidative addition)

Fluorinated compounds are widely used in the semiconductor and pharmaceutical industries. Their applications include electronic materials, solvents, lubricants and phase-transfer catalysts. Despite their many applications, their formation is not trivial. In particular, transition-metal catalysed cross-coupling reactions (e.g. Sonogashira, Heck, Suzuki) to generate carbon-carbon bonds with fluorinated substrates are often hampered by the formation of strong metal-carbon bonds and other competitive processes. In 2001, Espinet and Milstein reported Heck catalysis with fluorinated aryl-halides, while the use of non-fluorinated substrates had already been known for four decades. Likewise, it took about two decades after the initial report on the Sonogashira reaction to apply it to fluorinated substrates.

One commonly observed by-product of cross-coupling reactions is hydrodehalogenation of fluorinated aryl-halides, which affects the efficiency and selectivity of the overall catalytic process. The Marie Curie fellow, Dr Joyanta Choudhury, obtained detailed mechanistic information regarding some of the key steps involved in the Sonogashira and related cross-coupling reactions with fluorinated aryl-halides. These results have been submitted for publication as a communication. Another related manuscript about the activation of aryl-halides bonds by palladium is in preparation. The research results are most likely applicable to a wide range of processes with fluorinated aryl-halides and platinum-group metals.

This Marie Curie project generated also series of new materials which have been used by the fellow to study thin film formation, demonstrate Boolean logic and fabricate solar cells. These results have already been reported: Angew. Chem. Int. Ed. 2010, 49, 4780-4783; J. Am. Chem. Soc. 2010, 132, 9295-9297; J. Am. Chem. Soc. 2010, ASAP DOI: 10.1021/ja104695p. The development of molecular-based systems capable of information processing is a rapidly developing field. Functionality can be rationally designed on the basis of an understanding of the structures involved. Therefore, the role of the molecular structure and reaction parameters on the nature of thin-film growth was studied as well. Our electrochromic films are generated using a versatile two-step assembly method with organic and metal-organic chromophores cross-linked with palladium. The polypyridyl complexes exhibit exponential growth, whereas, under identical conditions, organic chromophores exhibit linear behaviour. The internal film morphology plays a key role in the storage and usage of the palladium, where a more porous structure results in exponential growth. Interestingly, through proper tuning of the reaction conditions, the growth of the molecular assemblies can be controlled, resulting in a changeover from exponential to linear growth. These findings unequivocally demonstrate the importance of both the internal film structure and deposition conditions on the assembly of functional molecular-based films.

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