The bis(dihydrogen) complex RuH2(H2)2(PCy3)2 (1) reacts with the disilanes (R2SiH)2X to produce
the dihydride complexes [RuH2{(η2-HSiR2)2X}(PCy3)2] (with R = Me and X = O (2a), C6H4 (3), (CH2)2 (4),
(CH2)3 (5), OSiMe2O (6)) and R = Ph, X = O (2b)). In these complexes, the bis(silane) ligand is coordinated
to ruthenium via two σ-Si−H bonds, as shown by NMR, IR, and X-ray data and by theoretical calculations.
3, 4, and 6 were characterized by X-ray diffraction. In the free disilanes the Si−H bond distances and the
J
Si
-
H values are around 1.49 Å and 200 Hz, respectively, whereas in the new complexes the values are in the
range 1.73−1.98 Å and 22−82 Hz, respectively for the σ-Si−H bonds. The importance of nonbonding H···Si
interactions, which control the observed cis geometry of the two bulky PCy3 ligands, is highlighted by X-ray
data and theoretical calculations. The series of bis(silane) model complexes, RuH2{(η2-HSiR2)2X}(PR‘3)2, with
X = (CH)2, C6H4, (CH2)
n
, O, and OSiH2O, and with R and R‘ = H or Me, was investigated by density
functional theory (DFT) by means of two hybrid functionals B3LYP and B3PW91. In the case of X = C6H4
three isomers were studied, the most stable of which has C
2
v
symmetry and whose structure closely resembles
the X-ray structure of 3. Calculated binding energies for the bis(silane) ligand to the RuH2(PH3)2 fragment
vary from 130 to 192 kJ/mol, showing that in the more stable complexes, the Si−H bonds are bound more
strongly than dihydrogen. The dynamic behavior of these complexes has been studied by variable temperature
1H and 31P{1H} NMR spectroscopy and exchange between the two types of hydrogen is characterized by
barriers of 47.5 to 68.4 kJ/mol. The effect of the bridging group X between the 2 silicons is illustrated by
reactions of compounds 2−6 with H2, CO, tBuNC. 3 is by far the most stable complex as no reaction occurred
even in the presence of CO, whereas elimination of the corresponding disilane and formation of RuH2(H2)2(PCy3)2, RuH2(CO)2(PCy3)2, or RuH2(tBuNC)2(PCy3)2 were observed in the case of 2 and 4−6. The mixed
phosphine complexes [RuH2{(η2-HSiMe2)2X}(PCy3)(PR3)] 3R−6R (with R = Ph and R = pyl) have been
isolated in good yields (80−85%) and fully characterized by the addition of 1 equiv of the desired phosphine
to 3−6. In the case of 4Ph, an X-ray determination was obtained. In the case of 2, elimination of the disiloxane
was always observed. Addition of 1 equiv of a disilane to Ru(COD)(COT) in the presence of 2 equiv of the
desired phosphine under an H2 atmosphere produces the complexes [RuH2{(η2-HSiMe2)2X}(PR3)2] (X = C6H4,
R = Ph (3Ph2) and R = pyl (3pyl2); X = (CH2)2, R = Ph, 4Ph2; R = pyl, 4pyl2). 4Ph2 was also characterized
by an X-ray structure determination.
