Exchange processes in complexes with two ruthenium (η2-Silane) linkages:: Role of the secondary interactions between silicon and hydrogen atoms

NMR studies and DFT calculations: (B3LYP) are used to elucidate the mechanisms for the hydride/(eta(2)-Si-H) hydrogen exchange observed in the bis(silane) complexes RuH2[(eta(2)-HSiMe2)(2)(CH2)(2)](PCY3)(2) (2) and RuH2 [eta(2)-HSiPh2)(2)O](PCY3)(2) (4) obtained from the reactions of the bis(dihydrogen) ruthenium complex, RuH2(H-2)(2)(PCY3)(2) (1) with the corresponding disilane HMe2Si(CH2)(2)SiMe2H or disiloxane HSiPh2OSiPh2H. Evidence is presented that exchange in 2 occurs via formation of isomers with dihydrogen ligands.. Conversion of the most stable isomer A with C-2v symmetry to the asymmetric Ru(eta(2)-SiH)(2) isomer B is the prelude to formation of the Ru(eta(2)-SiH)(eta(2)-H-2),isomer C and the. Ru(eta(2)-H-2)2 isomer D. Exchange occurs. via rotation of the dihydrogen ligands and reversal of the isomerization process., The transformation of A into B. via TSAB is the most energetically demanding. individual step. This corresponds,to the breaking of the SISHA (secondary interactions between silicon and hydrogen atoms) interactions'. between the silicons and the.,classical hydrides Hb and Hc. The calculated barrier of 43 kJ/mol for the, complex with CH2SiCH2-CH2SiH3 and PH3 ligands compares to the experimental enthalpy, of activation of 77 +/- 11 kJ/moL for 2. Whereas complex 2 adopts a geometry with C-2v symmetry,, low-temperature NMR spectroscopy shows that, complex 4 is present as two isomers, an asymmetric isomer with :C-1 symmetry and the symmetric isomer in proportions of ca. 1:2. The pathways for interconversion of the isomers and for exchange between the, hydride and SiH hydrogen atoms have been delineated by DFT calculations and resemble those for complex 2. Reaction of 4 with excess triphenylphosphine yields RuH2{(eta(2)-H-SiPh2)O(SiHPh2)}(PPh3)(3) (5), which is shown by NMR spectroscopy to contain one coordinated and, one uncoordinated SiH group. A crystal structure of the partially hydrolyzed analogue RuH2{(eta(2)-H-SiPh2)O(Si(OH)Ph-2)}-(PPh3)(3) (6) confirms the assignment. A ruthenium(II) formulation;with one (eta(2)-SiH) bond and two SISHA interactions is favored over a ruthenium(I V) structure with three hydrides and a silyl ligand.