Electron rich phosphines possessing sterically demanding substituents have gained attention of late for their ability to act as privileged ligands for palladium-catalyzed cross-coupling reactions. It has previously been shown in our group that neopentylphosphines have the ability to activate palladium complexes to act as a catalyst in the coupling of aryl bromides and chlorides to the alpha carbon of simple ketones. Calculated cone angles based on LPd(0) complexes show that trineopentylphosphine (TNpP) is larger than  tert-butyldineopentylphosphine (TBDNpP) which is in turn larger than di(tert-butyl)neopentylphosphine (DTBNpP). Though the neopentyl substituent can be sterically demanding, it is conformationally flexible. This conformational flexibility of the neopentyl group is hypothesized to allow TNpP derived catalysts to be less sensitive to sterically demanding substrates. Herein we report the use of these neopentylphosphine ligands in palladium catalyzed cross-coupling reactions of both sterically hindered and unhindered aryl bromides with a variety of malonate derivatives. Malonates are more challenging substrates than monoketones because they have the ability to chelate to the palladium active species.

Application of conformationally flexible neopentylphosphine ligands to palladium-catalyzed cross-coupling reactions of malonates with aryl halides

245th National Meeting (2013)

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