Six FeIII centers are incorporated into the tungstophosphate anion [H2P2W12O48]12− upon reaction with FeCl3. The {P2W12Fe6} unit thus formed has been characterized in [H4P2W12Fe9O56(OAc)7]6− and [H56P8W48Fe28O248]28−. The latter is a supramolecular polyoxotungstate in which each of the four {P2W12Fe6} units is connected by three Fe‐O‐Fe bridges (see structure). Magnetic studies indicate strong antiferromagnetic coupling between the FeIII centers.
The regioselectivity of the Heck reaction is supposed to be highly affected by the electronic properties of the alkene and the ionic or neutral character of the aryl palladium(II) complexes involved in the reaction with alkenes. In Heck reactions performed in dmf, [Pd(dppp){dppp(O)}Ph](+) (dppp=1,2-bis(diphenylphosphino)propane) is generated in the oxidative addition of PhI with [Pd(0)(dppp)(OAc)](-) formed in situ from Pd(OAc)(2) associated to two equivalents of dppp. [Pd(dppp){dppp(O)}Ph](+) is not very reactive with alkenes (styrene or methyl acrylate); however, it reacts with iodide ions (released in the catalytic reactions) to give [Pd(dppp)IPh] and with acetate ions (used as base) to give [Pd(dppp)(OAc)Ph]. [Pd(dppp)(OAc)Ph] reacts with styrene and methyl acrylate exclusively by an ionic mechanism, that is, via the cationic complex [Pd(dppp)(dmf)Ph](+) formed by dissociation of the acetate ion. The reaction of [Pd(dppp)IPh] is more complex and substrate dependent. It reacts with styrene exclusively by the ionic mechanism via [Pd(dppp)(dmf)Ph](+). [Pd(dppp)IPh] (neutral mechanism) and [Pd(dppp)(dmf)Ph](+) (ionic mechanism) react in parallel with methyl acrylate. [Pd(dppp)(dmf)Ph](+) is more reactive than [Pd(dppp)IPh] but is always generated at lower concentration.
Two main intermediate complexes, PhPd(OAc)(dppp) and PhPdI(dppp), are generated in palladiumcatalyzed Heck reactions performed from PhI and an acetate salt used as a base, in DMF. Both complexes react with the electron-rich alkene isobutyl vinyl ether (CH 2 dCHO i Bu) exclusively by an ionic mechanism, i.e., via the cationic complex [PhPd(dppp)(DMF)] + formed by dissociation of AcOor Ifrom the parent complexes, as already established for the reaction of PhPd(OAc)(dppp) with styrene and methyl acrylate and the reaction of PhPdI(dppp) with styrene. A mechanism is proposed which rationalizes the regioselectivity observed when reacting the electron-rich isobutylvinyl ether in palladium-catalyzed Heck reactions.
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