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.