Arene block metal

In conclusion, q -arene transition metal complexes have demonstrated their unique potential for organic synthesis. In particular, planar-chiral q -arene-Cr(CO)3 complexes are valuable building blocks for the diastereo- and enanti-oselective synthesis of complex natural products and related bioactive compounds. Highly original and competitive overall syntheses of various classes of natural products have been developed. The expenditure spent for the introduction of the metal fragment pays off especially in those cases, where the various chemical and stereochemical effects of the metal unit can be exploited in several subsequent transformations. Besides arene-Cr(CO)3 complexes, cationic arene-RuCp complexes have also been applied in synthesis, especially as they allow for efficient arylether formation under mild conditions. 

Arene(tricarbonyl)chromium complexes undergo a number of synthetically important transformations not usually observed for uncomplexed arenes. The chromium tricarbonyl moiety facilitates nucleophilic, electrophilic, and radical reactions at the benzylic position. Upon complexation, one side of the aromatic ring and adjacent functionalities is blocked by the metal carbonyl moiety and highly stereoselective reactions are usually observed even at relatively remote positions. In addition, the protons of the complexed aromatic ring have a substantially higher acidity and are readily removed and further substituted by electrophiles. Finally, the aromatic ring is activated toward addition reactions using a variety of nucleophiles. 

Iron-arene complexes are known to exhibit extremely high photoactivity as initiators. Quantum efficiencies have been found to be greater than I in the photopolymerisation of dicyanate esters. Phenylglycine derivatives have been found to be excellent co-synergists for the iron-arene complexes when used in conjunction with dyes and amines. Complexes of various types have also been proposed. Maleic anhydride-THF complexes have been used for the photopolymerisation of oligourethane acrylates while metal-ion complexes of spiropyran copolymers undergo reversible polymer precipitation. Azo and polyazo initiators have been used to make butadiene-isoprene block copolymers while charge-transfer complexes of morpholine-chlorine induce the radical polymerisation of methyl methacrylate. The presence of zinc chloride enhances the... 

A chiral auxiliary can also be positioned on the arene ring itself [96,141,142]. Addition of nucleophiles then proceeds regioselectively away from the metal and on the side not blocked by the methyl group of this auxiliary. Reversal of the selectivity for certain nucleophiles is not well understood. 

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