Activation of Chlorosilanes at Ruthenium: A Route to Silyl σ-Dihydrogen Complexes

The hydrido σ-dihydrogen complex RuClH(η2-H2)(PCy3)2 (2) reacts with the chlorosilanes HSiMe3-nCln (n = 1−3) to form the corresponding silyl σ-dihydrogen complexes RuCl(SiMe3-nCln)(η2-H2)(PCy3)2 (3Me3-nCln). These complexes display a 16-electron configuration, as shown by NMR, by X-ray data in the case of 3MeCl2, and by theoretical calculations. The σ-H2 ligand in 3MeCl2 has been located by X-ray diffraction, and the H−H distance of 1.05(3) Å compares well with the value obtained by DFT/B3PW91 (1.073 Å) as well as with the value of 1.08 ± 0.01 Å derived from the measurement of the JHD coupling constant of 17.5 Hz for the deuterated isotopomer RuCl(SiMeCl2)(η2-HD)(PCy3)2. The series of model complexes RuCl(SiMe3-nCln)(η2-H2)(PMe3)2 (S3Me3-nCln) was investigated by DFT at the B3PW91 level. The most stable isomers have a structure that resembles the X-ray structure of 3MeCl2: i.e., a silyl σ-dihydrogen formulation. In the case of S3Me2Cl and S3MeCl2 a second minimum very close in energy was optimized and formulated as a hydrido σ-silane species. The influence of the number of Cl substituents on Si and their location have been analyzed. The difference between 3Me2Cl on one side and 3MeCl2 and 3Cl3 on the other side is highlighted both by NMR and DFT data and by their reactivity toward ethylene. No reaction was observed for the latter complexes, whereas reaction with 3Me2Cl produces the hydrido η2-ethylene complex RuClH(C2H4)(PCy3)2 (4). In the case of styrene, the arene complex RuCl(SiMe2Cl)(η6-C8H10)(PCy3) (5) was isolated.