A series of 3,4-dicarboethoxy-N-pyrrolyl phosphine ligands (R2P−NC4H2(CO2Et)2) is described. A number of techniques, including reaction calorimetry, infrared spectroscopy, and X-ray crystallography, demonstrate that these ligands are potent π-acceptors and that the electronic substituent parameter χi for the 3,4-(EtO2C)2C4H2N moiety is ca. 16, placing it in a position between fluorine and chlorine.

The fluoroaryl phosphines P{C6H3(CF3)2-3,5}3 (La) and P(C6F5)3 (Lb) form the complexes trans-[MCl2(La)2] and trans-[MCl2(Lb)2](M = Pd or Pt) which have been isolated and fully characterised. 31P NMR studies of competition experiments show that the stability of trans-[PdCl2L2] is in the order L = Lb< La

No abstract