Pentamethylcyclopentadienyl ruthenium “pogo stick” complexes with nitrogen donor ligands

The half-sandwich 1,3-bis(trimethylsilyl)allyl and bis(trimethylsilyl)amido ruthenium complexes [(η⁵-C₅Me₅)RuX] (X = η³-C₃H₃(SiMe₃)₂, 1; X = N(SiMe₃)₂, 2) were prepared by reaction of tetranuclear [(η⁵-C₅Me₅)RuCl]₄ with four equivalents of K[C₃H₃(SiMe₃)₂] or Na[N(SiMe₃)₂]. Complexes 1 and 2 are formally 16- and 14-electron complexes, respectively, and exhibit γ-agostic C–H⋯Ru interactions in the solid state, which were further investigated by density functional theory (DFT) calculations and quantum theory of atoms in molecules (QTAIM) analysis. The acid–base reaction of the amido complex 2 with 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im^DippNH) afforded the imidazolin-2-iminato complex [(η⁵-C₅Me₅)Ru(NIm^Dipp)] (4); 4 was also obtained from the reaction of [(η⁵-C₅Me₅)RuCl]₄ with the lithium reagent [(Im^DippN)Li]₂. 4 represents the first terminal imidazolin-2-iminato complex with a late transition metal and shows a rare one-legged piano stool (“pogo stick”) geometry with a short Ru–N bond of 1.8607(15) Å. The reaction of 4 with tert-butyl isocyanate (tBuNCO) gave the ureato complex [(η⁵-C₅Me₅)Ru{Im^DippN(CO)NtBu}] (5) by [2 + 2] cycloaddition. This reactivity together with a DFT study on the bonding situation in 4 suggest a close similarity with related half-sandwich imido complexes [(arene)M(NR)] (M = Ru, Os) and [CpM(NR)] (M = Rh, Ir).