Nature of Si–H Interactions in a Series of Ruthenium Silazane Complexes Using Multinuclear Solid-State NMR and Neutron Diffraction

Three new N-heterocyclic-silazane compounds, 1a–c, were prepared and employed as bidentate ligands to ruthenium, resulting in a series of [Ru­(H)­{(κ-Si,N-(SiMe2-N-heterocycle)}3] complexes (3a–c) featuring the same RuSi3H motif. Detailed structural characterization of the RuSi3H complexes with X-ray diffraction, and in the case of triazabicyclo complex [Ru­(H)­{κ-Si,N-(SiMe2)­(C7H12N3)}3] (3a), neutron diffraction, enabled a reliable description of the molecular geometry. The hydride ligand of (3a) is located closer to two of the silicon atoms than it is to the third. Such a geometry differs from that of the previously reported complex [Ru­(H)­{(κ-Si,N-(SiMe2)­N­(SiMe2H)­(C5H4N)}3] (3d), also characterized by neutron diffraction, where the hydride was found to be equidistant from all three silicon atoms. A DFT study revealed that the symmetric and less regular isomers are essentially degenerate. Information on the dynamics and on the Ru···H···Si interactions was gained from multinuclear solid-state (1H wPMLG, 29Si CP MAS, and 2D 1H–29Si dipolar HETCOR experiments) and solution NMR studies. The corresponding intermediate complexes, [Ru­{κ-Si,N-(SiMe2-N-heterocycle)}­(η4-C8H12)­(η3-C8H11)] (2a–c), involving a single silazane ligand were isolated and characterized by multinuclear NMR and X-ray diffraction. Protonation of the RuSi3H complexes was also studied. Reaction of 3a with NH4PF6 gave rise to [Ru­(H)­(η2-H −SiMe2)­κ-N-(C7H12N3)­{κ-Si,N-(SiMe2)­(C7H12N3)}2]+[PF6]−(4aPF6) which was isolated and characterized by NMR spectroscopy, X-ray crystallography, and DFT studies. The nature of the Si–H interactions in this silazane series was analyzed in detail.