Relative stability of half-sandwich η6-benzene Ru(II) complexes of tridentate (2-pyridyl)alkylamine ligands of varying chelate ring-size: Nucleophilic addition of hydride ion onto the benzene ring

A full account of half-sandwich complexes of ruthenium(II) having three-legged “piano-stool” geometry supported by tridentate (2-pyridyl)alkylamine ligands is presented. Reaction of the dimer [{(η6-C6H6)RuCl(μ-Cl)}2] with N -methyl-N ,N -bis(2-pyridylmethyl)amine (MeL∗) in CH3OH in the presence of NH4PF6 affords the complex [(η6-C6H6)Ru(MeL∗)][PF6]2 (1). A similar reaction with N -methyl-N ,N -bis(2-pyridylethyl)amine (MeL∗∗), however, affords a non-organometallic Ru(III)-dimeric complex View the MathML source[(MeL∗∗)2Ru2III(μ-O)(μ-Cl)Cl2][PF6] (5) (the composition of this complex has been established by physicochemical method). Nucleophilic addition reaction on 1 with NaBH4 leads to the isolation of a cyclohexadienyl complex [(η5-C6H7)Ru(MeL∗)][PF6] (3). The molecular structure of 1 · 2CH3CN, 3, and previously reported cyclohexadienyl complex [(η5-C6H7)Ru(MeL)][PF6] (4) [MeL = N-methyl-[(2-pyridyl)ethyl(2-pyridyl)-methyl]amine], obtained from the reaction between NaBH4 and previously reported “piano-stool” complex [(η6-C6H6)Ru(MeL)][PF6]2 (2), has been confirmed by X-ray crystallography. Solution-state structure of new complexes 1 and 3 has been elucidated by their 1H NMR spectra in CD3CN. The behavior of complex 3 has been investigated with the aid of two-dimensional 1H NMR spectroscopy, as well. An attempt has been made to provide a rationale for the effect of supporting tridentate N-donor ligand [MeL, MeL∗, and MeL∗∗], varying in the chelate ring-size on (i) the relative stability of half-sandwich η6-benzene Ru(II) complexes and (ii) the electrophilicity of Ru(II)-coordinated benzene ring on the nucleophilic addition reactions.