Cis and Trans Isomers of Pt(SiHAr₂)₂(PR₃)₂(R = Me, Et) in the Solid State and in Solutions

Abstract

trans-Pt(SiHPh2)2(PMe3)2 (1) is prepared from the reaction of H2SiPh2 with cis-PtEt2(PMe3)2 and is characterized by X-ray crystallography. Dissolution of 1 in THF-d8 or CD2Cl2 causes its isomerization into cis-Pt(SiHPh2)2(PMe3)2, which is equilibrated to 1 in the solutions. Temperature-dependent 1H NMR spectra of a mixture of the isomers provided thermodynamic parameters for the trans to cis isomerization, ΔH° = 5.7(3) kJ mol-1 and ΔS° = 6.7(7) J mol-1K-1 in CD2Cl2 and ΔH° = 3.8(2) kJ mol-1 and ΔS° = 3.5(6) J mol-1K-1 at 298 K in THF-d8, respectively. The reactions of H2SiAr2 with Pt(PEt3)4 give cis-Pt(SiHAr2)2(PEt3)2 (2, Ar = C6H5; 3, Ar = C6H4F-p), which are considerably more stable than the trans isomers in CD2Cl2 (ca. 96:4 in an equilibrated CD2Cl2 solution of Pt(SiHPh2)2(PEt3)2 at room temperature).