Platinum-silicon four-membered rings of two different structural types

The synthesis and characterization of platinum-silicon four-membered rings of two different structural types is reported. The reaction of Pt(PR3)(3) ( R = Et or Pr) and Si(Hex)Ha (Hex = n-hexyl) gives [Pt(PR3)(2)SiH(Hex)](2) ( R = Et, 1a; R = Pr, 1b) and [(R3P)Pt(mu-Si(mu-H)(Hex)(Pt(PR3)(2))H)](2) (R = Et, 2a; R = Pr, 2b). The ratio of 1a to 2a is highly dependent on the rea ction conditions, whereas 1b is always the major product in the PPr3 substi tuted case. Evidence that suggests that 1a and 1b are precursors to 2a and 2b, respectively, is presented. X-ray crystallography of the rings 1b and 2 a shows they contain short Si-Si and Pt-Pt contacts, respectively. The Si-2 9 NMR chemical shifts for the two types of rings differ by over 250 ppm. A SD-NMR study of these rings has provided detailed coupling information, inc luding information on the agostic Pt-H-Si hydride in 2a.