Author/s: A. Sousa-Pedrares, C. Viñas, F. Teixidor
Reference: Chemical Communications, 2010, 46 (17), 2998-3000.
Reference: Chemical Communications, 2010, 46 (17), 2998-3000.
Abstract:
This communication reports the first use of the Wittig reaction to produce alkenylcarbaboranes. Carbaboranes are cluster compounds with ten boron and two adjacent carbon atoms in an icosahedral arrangement. Different methods for incorporating this unit into various substrates have been developed and their properties studied. Therefore, it is very useful to develop efficient methodologies that lead to the formation of carbaborane derivatives functionalized either through C or B that can be used for applications. Although carbaborane moieties have been successfully attached to a wide range of residues, the connection of o-carbaborane as a reagent to aromatic or conjugated systems has turned out to be particularly difficult. However, some molecules containing a carbaborane moiety linked to an organic fragment through a conjugated spacer exhibit nonlinear optical behaviour and have attracted great interest due to their applications.The conjugated linker is very important as it provides electronic coupling between the bridged units, thus permitting intercomponent processes. Several alkenyl linkers between the carbaborane unit and the donor group have been investigated. The Wittig reaction allows the preparation of an alkene by the reaction of an aldehyde or ketone with a triphenyl phosphonium ylide. The phosphonium ylide is prepared in situ by deprotonation of the corresponding phosphonium halide, which is in turn prepared by the reaction of triphenylphosphine with an alkyl halide. Despite the possibilities the Wittig reaction offers in organic chemistry, it has never been used to generate an alkenyl group bonded to the o-carbaborane. The strong electronwithdrawing character of the carboranyl group could have prevented this reaction. With this communication we provide first evidence that this is not the case and that the Wittig reaction is a real option to produce (C)-carbaborane alkenyl moities.