posted on 2009-06-10, 00:00authored byMary Grellier, Tahra Ayed, Jean-Claude Barthelat, Alberto Albinati, Sax Mason, Laure Vendier, Yannick Coppel, Sylviane Sabo-Etienne
The novel disilazane compound 2-pyridinetetramethyldisilazane (1) has been synthesized. The competition between N-pyridine coordination and Si−H bond activation was studied
through its reactivity with two ruthenium complexes. The reaction
between 1 and RuH2(H2)2(PCy3)2 led to the isolation of the new complex
RuH2{(η2-HSiMe2)N(κN-C5H4N)(SiMe2H)}(PCy3)2 (2) resulting from the loss of
two dihydrogen ligands and coordination of 1 to the ruthenium
center via a κ2N,(η2-Si−H)
mode. Complex 2 has been characterized by multinuclear
NMR experiments (1H, 31P, 13C, 29Si), X-ray diffraction and DFT studies. In particular, the
HMBC 29Si−1H spectrum supports the presence
of two different silicon environments: one Si−H bond is dangling,
whereas the other one is η2-coordinated to the ruthenium
with a JSiH value of 50 Hz. DFT calculations
(B3PW91) were also carried out to evaluate the stability of the agostic
species versus a formulation corresponding to a bis(σ-Si−H)
isomer and confirmed that N-coordination overcomes any stabilization
that could be gained by the establishment of SISHA interactions. There
is no exchange between the two Si−H bonds present in 2, as demonstrated by deuterium-labeling experiments. Heating 2 at 70 °C under vacuum for 24 h, leads to the formal
loss of one equivalent of H2 from 2 and formation
of the 16-electron complex RuH{(SiMe2)N(κN-C5H4N)(SiMe2H)}(PCy3)2 (3) formulated as a hydrido(silyl)
species on the basis of multinuclear NMR experiments. The dehydrogenation
reaction is fully reversible under dihydrogen atmosphere. Reaction
of Ru(COD)(COT) with 3 equiv of 1 under a H2 pressure led to the isolation of the new complex RuH{(SiMe2)N(κN-C5H4N)(SiMe2H)}3 (4) characterized as a hydridotrisilyl
complex by multinuclear NMR techniques, X-ray and neutron diffractions,
as well as DFT calculations. The 29Si HMBC experiments
confirm the presence of two different silicon atoms in 4, with a signal at −14.64 ppm for three dangling Si-Me2H fragments and a signal at 64.94 ppm (correlating
with the hydride signal) assigned to three Si-Me2N groups bound to Ru. Comparison of DFT and neutron parameters
involving the hydride clearly indicates an excellent correlation.
The Si−H distance of ∼2.15 Å is much shorter than
the sum of the van der Waals radii and typically in the range of a
significant interaction between a silicon and a hydrogen atom (SISHA
interactions). In 4, three dangling Si−H groups
remain accessible for further functionalization.