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

Abstract

Methyl-, phenyl-, and n -butyltin trichloride RSnCl 3 (R = Me, Ph, n Bu) react selectivily with palladium(0)−phosphine precursors through the unprecedented oxidative addition of the Sn−C bond. With [Pd(2-PyPPh 2 ) 3 ] (2-PyPPh 2 = 2-pyridyldiphenylphoshine), the reaction cleanly leads to stable cationic dichlorostannylene palladium complexes of the general formula trans -[PdR(SnCl 2 (2-PyPPh 2 ) 2 )][X] (X = Cl, R = Me ([ 5 ]Cl), R = Ph ([ 6 ]Cl), R = n Bu ([ 11 ]Cl); X = RSnCl 4, R = Me ([ 5 ][MeSnCl 4 ]), R = Ph ([ 6 ][PhSnCl 4 ]), R = n Bu ([ 11 ][ n BuSnCl 4 ])). The SnCl 2 (2-PyPPh 2 ) 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 ][ n BuSnCl 4 ], containing a Pd− n Bu moiety, was found to be stable up to 70 °C. Oxidative addition of SnCl 4 on [Pd(2-PyPPh 2 ) 3 ] resulted in trans -[PdCl(SnCl 2 (2-PyPPh 2 ) 2 )]Cl ([ 7 ]Cl) and trans -[PdCl(SnCl 3 (2-PyPPh 2 ) 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 RSnCl 3 on [Pd(PPh 3 ) 4 ] resulted in palladium trichlorostannyl complexes that were not stable toward cis − trans isomerization, (partial) elimination of SnCl 2 (R = Me, Ph), or β-H elimination (R = n Bu). The resulting mixtures of palladium alkyl and palladium hydride species were analyzed by multinuclear NMR, resulting in the identification of novel cis- [PdMe(SnCl 3 )(PPh 3 ) 2 ] ( cis - 4 ), trans- [PdMe(SnCl 3 )(PPh 3 ) 2 ] ( trans- 4 ), and cis -[PdH(SnCl 3 )(PPh 3 ) 2 ] ( cis - 10 ) along with previously observed trans -[PdPh(Cl)(PPh 3 ) 2 ] ( 1 ), trans -[PdMe(Cl)(PPh 3 ) 2 ] ( 3 ), trans -[PdH(SnCl 3 )(PPh 3 ) 2 ] ( trans - 10 ), and trans- [PdH(Cl)(PPh 3 ) 2 ] ( 9 ).