Synthesis, characterisation and catalytic application of sol–gel processed cationic palladium(II) complexes

Abstract

The dicationic T-silyl functionalised bis(acetonitrile)(dppp)palladium(II) complex 2(T0) (see Scheme 1) was sol–gel processed with different amounts (y) of the co-condensation agent MeSi(OMe)2(CH2)6(MeO)2SiMe (D0-C6-D0) to give the new stationary phases 2a–h(Tn)(Di-C6-Di)y (y = 0, 5, 10, 15, 20, 40, 80, and 100; n = 0–3, i = 0–2). The polysiloxane matrices and the integrity of the palladium(II) complex centres were investigated by means of solid state NMR (29Si, 13C, 31P) and EXAFS spectroscopy. Dynamic NMR investigations show an increasing mobility of the hybrid polymers on going from y = 0 to 10. For higher amounts of the co-condensation agent MeSiOi/2(OX)2 − i(CH2)6Oi/2(XO)2 − iSiMe (Di-C6-Di) the mobility tends toward that of a matrix consisting of Di-C6-Di (T/D = 0) only. NMR experiments in suspension give further evidence for considerable mobility of the interphases (formed by the penetration of stationary and mobile phases on a molecular scale). Model reactions of 2a(Tn) with different isocyanides in the interphase point to almost complete accessibility of the palladium(II) centres, even if the reactants carry sterically demanding substituents (e.g.t-Bu). The activity of the hybrid catalysts 2a–h(Tn)(Di-C6-Di)y in the ethene/CO copolymerisation is markedly dependent on the temperature and the amount y of the co-condensation agent. A maximum of activity [1600 g(ECO) g(Pd)−1 h−1] is achieved with y = 10 which is 75% of the activity of the analogous homogeneous catalyst.