15703-03-4Relevant academic research and scientific papers
Study of PtX2(PR3)2 in the presence of PR3 in CH2Cl2 solution and the cis-trans isomerization reaction as studied by 31P NMR. Crystal structure of [PtCl(PMe3)3]Cl
Favez, Roland,Roulet, Raymond,Pinkerton, Alan A.,Schwarzenbach, Dieter
, p. 1356 - 1365 (2008/10/08)
The identity of the species present in dichloromethane solutions of PtX2L2 and L (L = PMe3, PEt3, P-n-Bu3, P(tol)3 where tol = p-tolyl; Pt:L ratios from 1:0.05 to 1:5) are cis- and trans-PtX2L2, [PtXL3]+ (X = Cl, Br), and [PtXL4]+ (X = Cl, Br, I; L = PMe3). The only species with three coordinated phosphines which is five-coordinate in solution is PtI2(PMe3)3, whose IR and NMR parameters are consistent with a square-pyramidal geometry having one phosphine in the apical position. All other tris complexes [PtXL3]+ are four-coordinate in solution as shown by UV and 31P NMR spectroscopy, and this geometry is also found in the solid state ([PtCl(PMe3)3]Cl X-ray crystal structure). The complexes [PtX(PMe3)4]+ have a square-pyramidal geometry with X in the apical position. In the case of L = PMe3,31P NMR studies show that intermolecular phosphine exchange occurs between [PtClL3]+, [PtClL4]+, PtI2L3, and free L, whose activation parameters, estimated from line-shape analysis, are reported. Contrary to previous reports, chloride ion is found to displace one phosphine from [PtClL3]+ ion, giving the cis-PtCl2L2 isomer in a fast step prior to cis-trans equilibration. The results indicate that the cis-trans isomerization of PtX2L2 catalyzed by L proceeds by rapid displacement of X- by L followed by slow displacement of L by X- and not by pseudorotation of a five-coordinate intermediate. A similar mechanism was established for the isomerization of the alkyl complex PtCl(CH2CN)(PPh3)2.
