Iminophosphine–palladium(0) complexes as catalysts for the Stille reaction

The cross-coupling of iodobenzene with tributylphenylethynylstannane or tributylvinylstannane is efficiently catalysed by iminophosphine–palladium(0)–olefin complexes of the type [Pd(η2-dmf)(P-N)] (dmf, dimethylfumarate; P-N, 1-(PPh2)-C6H4-2-CNR (R=alkyl, aryl)). The catalytic activity depends on the R substituent of the imino group: the highest reaction rates are obtained using aryl-substituted iminophosphines. Equivalent catalytic systems can be obtained using a palladium source such as Pd(OAc)2 or Pd(dba)2 (dibenzylideneacetone, dba) in combination with the iminophosphine ligands. In the coupling of iodobenzene with tributylphenylethynylstannane, the highest reaction rates are obtained using an iminophosphine/palladium molar ratio of 2:1, while in the vinylstannane–iodobenzene coupling the best P-N/Pd ratio is 1:1.