Versatile Coordination of 2-Pyridinetetramethyldisilazane at Ruthenium: Ru(II) vs Ru(IV) As Evidenced by NMR, X-ray, Neutron, and DFT Studies

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(H-2)(2)(PCy3)(2) led to the isolation of the new complex RuH2{(eta(2)-HSiMe2)N(kappa N-C5H4N)(SiMe2H)}(PCy3)(2) (2) resulting from the loss of two dihydrogen ligands and coordination of 1 to the ruthenium center via a kappa N-2,(eta(2)-Si-H) mode. Complex 2 has been characterized by multinuclear NMR experiments (H-1, P-31, C-13, Si-29), X-ray diffraction and DFT studies. In particular, the HMBC Si-29-H-1 spectrum supports the presence of two different silicon environments: one Si-H bond is dangling, whereas the other one is eta(2)-coordinated to the ruthenium with a J(SiH) 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(sigma-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 degrees C under vacuum for 24 h, leads to the formal loss of one equivalent of H-2 from 2 and formation of the 16-electron complex RuH{(SiMe2)N(kappa N-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 H-2 pressure led to the isolation of the new complex RuH{(SiMe2)N(kappa N-C5H4N)(SiMe2H)}(3) (4) characterized as a hydridotrisilyl complex by multinuclear NMR techniques, X-ray and neutron diffractions, as well as DFT calculations. The Si-29 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 similar to 2.15 angstrom 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.