Relative stability of half-sandwich η 6-benzene Ru(II) complexes of tridentate (2-pyridyl)alkylamine ligands of varying chelate ring-size: Nucleophilic addition of hydride ion onto the benzene ring

Abstract

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 [{(η 6-C 6H 6)RuCl(μ-Cl)} 2] with N-methyl- N, N-bis(2-pyridylmethyl)amine (MeL ∗) in CH 3OH in the presence of NH 4PF 6 affords the complex [(η 6-C 6H 6)Ru(MeL ∗)][PF 6] 2 ( 1). A similar reaction with N-methyl- N, N-bis(2-pyridylethyl)amine (MeL ∗∗), however, affords a non-organometallic Ru(III)-dimeric complex [ ( MeL ∗ ∗ ) 2 Ru 2 III ( μ -O ) ( μ -Cl ) Cl 2 ] [ PF 6 ] ( 5) (the composition of this complex has been established by physicochemical method). Nucleophilic addition reaction on 1 with NaBH 4 leads to the isolation of a cyclohexadienyl complex [(η 5-C 6H 7)Ru(MeL ∗)][PF 6] ( 3). The molecular structure of 1 · 2CH 3CN, 3, and previously reported cyclohexadienyl complex [(η 5-C 6H 7)Ru(MeL)][PF 6] ( 4) [MeL = N-methyl-[(2-pyridyl)ethyl(2-pyridyl)-methyl]amine], obtained from the reaction between NaBH 4 and previously reported “piano-stool” complex [(η 6-C 6H 6)Ru(MeL)][PF 6] 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 CD 3CN. 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 η 6-benzene Ru(II) complexes and (ii) the electrophilicity of Ru(II)-coordinated benzene ring on the nucleophilic addition reactions.