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(PR 3 ) 3 (R = Et or Pr) and Si(Hex)H 3 (Hex = n -hexyl) gives [Pt(PR 3 ) 2 SiH(Hex)] 2 (R = Et, 1a; R = Pr, 1b ) and [(R 3 P)Pt(μ-Si(μ-H)(Hex)(Pt(PR 3 ) 2 )H)] 2 (R = Et, 2a; R = Pr, 2b ). The ratio of 1a to 2a is highly dependent on the reaction conditions, whereas 1b is always the major product in the PPr 3 substituted 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 2a shows they contain short Si−Si and Pt−Pt contacts, respectively. The 29 Si NMR chemical shifts for the two types of rings differ by over 250 ppm. A 2D-NMR study of these rings has provided detailed coupling information, including information on the agostic Pt−H−Si hydride in 2a .