Cationic palladium eta(3)-allyl complexes with hemilabile P,O-ligands: Synthesis and reactivity. Insertion of ethylene into the Pd-allyl function

Cationic palladium allyl complexes [(eta(3)-C3H5)Pd(kappa(2)P boolean AND O)](SbF6-)-Sb-+(2[SbF6], P boolean AND O = Ph(2)P(CH2)(2)C(=O)OEt; 3[SbF6], o-Ph(2)PC(6)H(4)C(=O)OEt; 4[SbF6], Ph(2)P(CH2)(2)P(=O)Ph(2)) have been prepared. In all complexes the oxygen donor can be displaced by other ligands such as carbon monoxide and ethylene. Displacement of an ester donor occurs much more readily than displacement of the phosphine oxide function. Above 0 degrees C, the resulting ethylene complexes [(eta(3)-C3H5)Pd(C2H4)(kappa(1)P similar to O)](+) react to give (1,2,5-eta(3))-pent-1-en-5-yl complexes [(H2C=CH(CH2)(3)Pd(kappa(2)P boolean AND O)](+). A rate constant of e.g. k(17 degrees C) = (2.27 +/- 0.11) x 10(-4) s(-1) was determined for P,O = Ph(2)P(CH2)(2)C(O)OEt by H-1 NMR spectroscopy. Using 2-4 as catalyst precursors for ethylene dimerization, the allyl moiety is ultimately cleaved from the metal center as 1,4-pentadiene.