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)(CH 2 CH 2 CH 2 PPh 2 ) 2, “biPSiH”, with Ru(PPh 3 ) 2 (CO) 3 affords quantitatively the phosphinoalkylsilyl complex RuH(biPSi)(CO) 2, as a mixture of the crystallographically characterized syn diastereomer 3-s and its anti correspondent 3-a; subsequent treatment with CCl 4 then LiAl 2 H 4 provides access to the deuterioisotopomer Ru 2 H(biPSi)(CO) 2, 3- d 1 . Slow stereomutation of pure 3-s to an equilibrium mixture 3-s / 3-a (4.5:1, 295 K) occurs with Δ G ⧧ 295, 102(5) kJ mol - 1; Δ H ⧧ 295, 113(7) kJ mol - 1; Δ S ⧧ 295, 37(2) J K - 1 mol - 1; this is not accompanied by incorporation of external 13 CO, shows only a minor isotope effect vs 3- d 1, and is concluded to be nondissociative.