Thermal isomerization of mer-[RhH(SAr)(SiHAr'2)(PMe3)3] to fac- [RhH2{SiAr'2(SAr)}(pme3)3] involving thiolato group transfer from Rh to Si

Article abstract of DOI:10.1246/bcsj.71.2853

Heating of a benzene or toluene solution of mer- [RhH(SAr)(SiHAr'₂)(PMe3)₃] (Ar = C₆H₅, C₆H₄Me-p, C₆H₄OMe-p; Ar' = C₆H₅, C₆H₄Me-p, C₆H₄F-p, C₆H₄CF₃-p) at 30 - 50 °C gives fac-[RhH₂ {SiAr₂(SAr)}(PMe3)₃] quantitatively through thiolato group transfer from Rh to Si. X-Ray structural analysis of fac-[RhH₂{SiPh₂(SPh)}(PMe3)₃] reveals octahedral coordination with three PMe₃ ligands at facial coordination sites, while the J H NMR spectra show the presence of two equivalent hydrido ligands. The other Rh complexes are isolated or characterized in situ by means of NMR spectroscopy. The reaction of mer- [RhH(SC₆H₄Me-p)(SiHPh₂)(PMe₃)₃] to form the Rh complex obeys first- order kinetics with the kinetic parameters: ΔG(+) = 98.6 kJ mol^-1 ΔH(+), = 94.9 kJ mol^-1 and ΔS(+) = 1 12 J mol^-1 deg^-1 at 298 K. The rate constants of the reaction of mer-[RhH(SC₆H₄X-p)(SiHPh2)(PMe3)3] (X = H, Me, OMe) increase with increasing Hammett constant σ of substituent X. The substituent of the diarylsilyl ligand of mer-[RhH(SC₆H₄X-p){SiH(C₆H₄Y- p)₂}(PMe₃)3] (X = Me or OMe; Y = H, Me, F, CF₃) also influences the reaction rate constant, while the degree of enhancement is not directly related to the electron donating or withdrawing ability of substituent Y. Possible reaction mechanisms are discussed based on these results.