Trimethyl-silyl, -germyl and -stannyl complexes of platinum

Abstract

Two series of compounds (chelate)PtCl(MMe₃)(I) and (chelate)Pt(MMe₃)₂(II)[chelate =(Ph₂PCH₂)₂; M = Si, Ge, or Sn] have been isolated. For M = Si or Ge both are obtained by the reaction of (chelate)PtCl₂ with (Me₃M)₂Hg. Trimethylstannyl–platinum compounds have been isolated (a) by exchange reactions e.g. Pt–MMe₃+ Me₃SnH → Pt–SnMe₃+ Me₃MH (M = Si, Ge) and (b) from the oxidative addition of Me₃SnH to (chelate)₂Pt. Trimethylstannane adds reversibly to (I) and (II) when M = Sn yielding the octahedral complexes (chelate)Pt(H)(Cl)(SnMe₃)₂ and (chelate)Pt(H)(SnMe₃)₃ respectively. Stepwise hydrogen chloride cleavage of Pt–MMe₃ groups has been investigated: the products from (chelate)Pt(MMe₃)₂ are (chelate)PtCl(MMe₃) and (chelate)PtCl₂. Hydrogenolysis of Pt–MMe₃ bonds proceeds readily when M = Si or Ge (1 atmos. H₂ and 25°). For the reaction (chelate)Pt(SiMe₃)₂+ H₂→(chelate)PtH(SiMe₃) the rate constant at 25° is ca. 5·0 × 10^–2 l mol^–1 s^–1, the reaction being first-order with respect to H₂ and (II). At 70° and 1 atoms. H₂ the second Me₃Si–Pt bond is hydrogenated to Me₃SiH and a platinum cluster compound, formulated as (chelate)₃Pt₄. Equilibrium constants have been derived for the hydrogenolysis of trans-(Et₃P)₂PtCl(SiMe₃). Exchange reactions of the types: Pt–SiMe₃+ Me₃GeH → Pt–GeMe₃+ Me₃SiH and Pt–GeMe₃+ Me₃SnH → Pt–SnMe₃+ Me₃GeH have been investigated; the position of equilibrium favours R₃M–Pt products in the order, Sn Ge > Si. Cleavage of Pt–M bonds by 1,2-dibromoethane is considered to involve an octahedral intermediate. ¹H n.m.r., i.r. and mass spectra of the various compounds and reactions are discussed.