Self-replication of tris(cyanoethyl)phosphine catalysed by platinum group metal complexes
Abstract
The platinum(0) complex [Pt(tcep)3], tcep = P(CH2CH2CN)3, catalyses the formation of tcep from PH3 and CH2CHCN. 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 CH2CHCN 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 31P-{1H} NMR spectroscopy. It is revealed that the kinetics are a complex function of the concentration of product tcep. Qualitatively, the rates also depend on [CH2CHCN] and [catalyst]. Both 31P-{1H} and 195Pt-{1H} NMR spectroscopy suggests that addition of CH2CHCN to [Pt(tcep)3] gives the complex [Pt(tcep)2(η2-CH2CHCN)] which undergoes phosphine exchange on the NMR time-scale. The binuclear complex [Pt2H2(tcep)2{µ-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(CH2CH2CN)2 with CH2CHCN. Two parallel mechanisms involving mononuclear and binuclear intermediates are discussed to rationalise these observations.