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Oxidative Addition of Sn−C Bonds on Palladium(0): Identification of Palladium−Stannyl Species and a Facile Synthetic Route to Diphosphinostannylene−Palladium Complexes

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posted on 2010-11-22, 00:00 authored by Yves Cabon, Irena Reboule, Martin Lutz, Robertus J. M. Klein Gebbink, Berth-Jan Deelman
Methyl-, phenyl-, and n-butyltin trichloride RSnCl3 (R = Me, Ph, nBu) react selectivily with palladium(0)−phosphine precursors through the unprecedented oxidative addition of the Sn−C bond. With [Pd(2-PyPPh2)3] (2-PyPPh2 = 2-pyridyldiphenylphoshine), the reaction cleanly leads to stable cationic dichlorostannylene palladium complexes of the general formula trans-[PdR(SnCl2(2-PyPPh2)2)][X] (X = Cl, R = Me ([5]Cl), R = Ph ([6]Cl), R = nBu ([11]Cl); X = RSnCl4, R = Me ([5][MeSnCl4]), R = Ph ([6][PhSnCl4]), R = nBu ([11][nBuSnCl4])). The SnCl2(2-PyPPh2)2 fragment, formed by intramolecular coordination of the pyridyl groups to the dichlorostannylene moiety, can be considered as a self-assembled pincer-type ligand with a remarkable ability to suppress β-H elimination in its Pd−alkyl derivatives: [11][nBuSnCl4], containing a Pd−nBu moiety, was found to be stable up to 70 °C. Oxidative addition of SnCl4 on [Pd(2-PyPPh2)3] resulted in trans-[PdCl(SnCl2(2-PyPPh2)2)]Cl ([7]Cl) and trans-[PdCl(SnCl3(2-PyPPh2)2)] (8). The molecular structure of 8 was determined by single-crystal X-ray crystallography, indicating that the Sn atom of the trichlorostannyl function has an octahedral coordination geometry. In contrast, oxidative addition of the Sn−C bond of RSnCl3 on [Pd(PPh3)4] resulted in palladium trichlorostannyl complexes that were not stable toward cistrans isomerization, (partial) elimination of SnCl2 (R = Me, Ph), or β-H elimination (R = nBu). The resulting mixtures of palladium alkyl and palladium hydride species were analyzed by multinuclear NMR, resulting in the identification of novel cis-[PdMe(SnCl3)(PPh3)2] (cis-4), trans-[PdMe(SnCl3)(PPh3)2] (trans-4), and cis-[PdH(SnCl3)(PPh3)2] (cis-10) along with previously observed trans-[PdPh(Cl)(PPh3)2] (1), trans-[PdMe(Cl)(PPh3)2] (3), trans-[PdH(SnCl3)(PPh3)2] (trans-10), and trans-[PdH(Cl)(PPh3)2] (9).