Self-replication of tris(cyanoethyl)phosphine catalysed by platinum group metal complexes

The platinum(0) complex [Pt(tcep)(3)], tcep = P(CH2CH2CN)(3), catalyses the formation of tcep from PH3 and CH2 = CHCN. The complexes [M(tcep)(3)] (M = Pt, Pd or Ni) and [MCl(tcep)(3)] (M = Rh or Ir) are compared for their catalysis of the reaction of PH(CH2CH2CN)(2) with CH2 = CHCN to give tcep and it is shown that the platinum(0) complex is the most efficient. The platinum(0) catalysis has been studied in detail, monitoring the kinetics by P-31-{H-1} NMR spectroscopy. It is revealed that the kinetics are a complex function of the concentration of product tcep. Qualitatively, the rates also depend on [CH2 = CHCN] and [catalyst]. Both P-31-{H-1} and Pt-195-{H-1} NMR spectroscopy suggests that addition of CH2 = CHCN to [Pt(tcep)(3)] gives the complex [Pt(tcep)(2)(eta(2)-CH2 = CHCN)] which undergoes phosphine exchange on the NMR time-scale. The binuclear complex [Pt2H2(tcep)(2){mu-P(CH2CH2CN)(2)}(2)], formed upon addition of PH(CH2CH2CN)(2) to trans-[PtHCl(tcep)(2)] in the presence of base, is shown to be a catalyst precursor for the reaction of PH(CH,CH,CN), with CH2 = CHCN. Two parallel mechanisms involving mononuclear and binuclear intermediates are discussed to rationalise these observations.