Stereomutation at an octahedral transition-metal center: Energetics of hydride transit between syn and anti faces of the bis(diphenylphosphinopropyl)(methyl)silyl (biPSi) complex RuH(biPSi)(CO)(2)

Reaction of SiH(Me)(CH2CH2CH2PPh2)(2), "bi-PSiH", with Ru(PPh3)(2)(CO)(3) a ffords quantitatively the phosphinoalkylsilyl complex RuH(biPSi)(CO)(2), as a mixture of the crystallographically characterized syn diastereomer 3-s a nd its anti correspondent 3-a; subsequent treatment with CCl4 then (LiAlH4) -H-2 provides access to the deuterioisotopomer (RuH)-H-2(biPSi)(CO)(2), 3-d (1). Slow stereomutation of pure 3-s to art equilibrium mixture 3-a/3-a (4. 5:1, 295 K) occurs with DeltaG(295)(double dagger), 102(5) kJ mol(-1); Delt aH(295)(double dagger), 113(7) kJ mol(-1); DeltaS(295)(double dagger), 37(2 ) J K-1 mol(-1); this is not accompanied by incorporation of external (CO)- C-13, shores only a minor isotope effect us 3-d(1), and is concluded to be nondissociative.