Small molecule binding versus stabilization of coordinatively unsaturated ruthenium-pincer complex by N2/solvent

Coordinatively unsaturated, [RuH(N₂/solv)(CO)(P^PhN^NpP^Ph)][BAr^F₄] complex (2), which is stabilized by either a weakly bound N₂/solvent molecule has been synthesized and characterized. Binding of N₂ ligand in the complex 2 was studied by Raman spectroscopy. The weakly coordinating N₂/solv in complex 2 could be easily displaced by sigma donor ligands leading to the corresponding cationic complexes, [RuH(L)(CO)(P^PhN^NpP^Ph)][BAr^F₄] (L = CH₃CN (3), CO (4) and H₃B^.NMe₃ (5)). Further, upon reacting complex 2 with H₂ resulted in the formation of [RuH(ƞ²-H₂)(CO)(P^PhN^NpP^Ph)][BAr^F₄] complex (6) in the temperature range of 243 K - 183 K. The intact nature of the H−H bond of H₂ ligand in complex 6 was established by variable-temperature (VT) ¹H spin-lattice relaxation time (T₁) measurements and J(H,D) coupling measurement of the HD isotopomer. Reaction of complex 2 with HSiRR’₂ (R = R’ =Et (7a), R = Ph, R’ = Me (7b)) resulted in the formation of the corresponding σ-silane complexes in the temperature range of 243 K - 183 K. Upon warming the reaction mixture above 243 K, the complex 2 and free silane were recovered showing that the binding of the Si−H bond is reversible. The interaction of the Si−H bond in HSiEt₃ and HSiMe₂Ph with the metal center was established by VT multinuclear NMR spectroscopy. Furthermore, when complex 2 was reacted with methane at high pressures (6 bar - 12 bar), no interaction between the ruthenium and C−H bond of methane was noted.