title: Stability and Unimolecular Reactivity of Palladate(II) Complexes [LnPdR3]-(L=Phosphine, R=Organyl, n=0 and 1).
abstract: The reduction of PdIIprecatalysts to catalytically active Pd0species is a key step in many palladium-mediated cross-coupling reactions. Besides phosphines, the stoichiometrically used organometallic reagents can afford this reduction, but do so in a poorly understood way. To elucidate the mechanism of this reaction, we have treated solutions of Pd(OAc)2and a phosphine ligand L in tetrahydrofuran with RMgCl (R=Ph, Bn, Bu) as well as other organometallic reagents. Analysis of these model systems by electrospray- ionization mass spectrometry found palladate(II) complexes [LnPdR3]-(n=0 and 1), thus pointing to the occurrence of transmetallation reactions. Upon gas-phase fragmentation, the [LnPdR3]-anions preferentially underwent a reductive elimination to yield Pd0species. The sequence of the transmetallation and reductive elimination, thus, constitutes a feasible mechanism for the reduction of the Pd(OAc)2precatalyst. Other species of interest observed include the PdIVcomplex [PdBn5]-, which did not fragment via a reductive elimination but lost BnH instead.
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany.
authors.forename: Marlene
authors.initials: M
authors.lastname: Kolter
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany. konrad.koszinowski@chemie.uni-goettingen.de.
authors.forename: Konrad
authors.initials: K
authors.lastname: Koszinowski
keywords: cross-coupling; gas-phase reactions; mass spectrometry; palladium; reactive intermediates