Exploiting the Potentiality of High Valent Transition Metal Halides in Organic Synthesis

Halides of group 5 and 6 transition metals in a +5 or +6 oxidation state (high valent metal halides, HVMH) are strong Lewis acids that can also exploit oxidizing power and halogenating ability, thus constituting potential mediators in various organic transformations. In the framework of our interest in the chemistry of HVMH with different organic functionalities, we have investigated the reactions with compounds bearing unsaturated C-N or C-O bonds. Activation products, like quinoxalinium and imidazolium salts, were obtained from the reactions of HVMH with a-diimines, as a result of intra-/inter-molecular couplings. Also, rare coordination complexes were isolated and characterized, including the first examples of high valent metal fluoride adducts with a-diimines. Unprecedented, “non-classical” coordination compounds were afforded from NbX5 (X = Cl, Br) and isocyanides. Furthermore, clean CO release at room temperature was observed for the first time from tertiary a-phenylcarboxylic acids upon interaction with HVMH, resulting in either the isolation of stable carbocation salts, or their conversion into more stable hydrocarbons.