Diruthenium complexes having a partially hydrogenated bipyridine ligand: plausible mechanism for the dehydrogenative coupling of pyridines at a diruthenium site

Abstract

Diruthenium complexes containing a partially hydrogenated bipyridine ligand are synthesized, which undergo dehydrogenation leading to the elimination of bipyridine.

Synthesis of a diruthenium μ-η4-α-diimine complex via dehydrogenative coupling of cyclic amines and its role in dehydrogenative oxidation of pyrrolidine

“…We have shown that related μ-η 2 -dhbpy complex 7d interconverts with μ-η 4 -dhbpy complex 8 , but the formation of 8 required a much longer period at 80 °C (84 h; Scheme 7). 28 Although we could not observe the corresponding hydrido species in the reaction with 1-pyrroline, dihydride species 7a was optimized using DFT calculation (Fig. S39†).…”

“…We reported that the μ-imidoyl complex 3c reacts with PMe 3 to yield phosphine adduct 6 . 28 In this reaction, a PMe 3 molecule is coordinated to the Ru atom, where the imidoyl carbon atom was σ-bonded, likely owing to the higher oxidation state of the Ru atom compared to that of the nitrogen-ligated Ru centre (Scheme 8a). Similar regioselectivity was observed for the reaction of triruthenium μ 3 -η 2 :η 2 (⊥)-imidoyl complex 9 with isocyanide forming isocyanide adduct 10 (Scheme 8b).…”

“…These structural features are consistent with those of the previously reported diruthenium μ-η 4 -α-diimine complexes 32–38 and the μ-4,4′-dimethylbipyridine complex [(Cp*Ru) 2 (μ-η 4 -4,4′-Me 2 bpy)] (4,4′-Me 2 bpy = 4,4′-dimethylbipyridine), which was synthesized by the reaction of [Cp*Ru(μ-H) 4 RuCp*] with γ-picoline. 28…”

“…The Ru(1)–Ru(2) distance ( 5a , 2.9274(4) Å; 5b , 2.9260(3) Å) is almost the same as that of the μ-η 4 -4,4′-Me 2 bpy complex [(Cp*Ru) 2 (μ-η 4 -4,4′-Me 2 bpy)] (2.9042(7) Å). 28 The presence of a direct Ru–Ru bond makes these complexes coordinatively saturated, according to the effective atomic number (EAN) rule. However, molecular orbitals associated with the bonding interaction between the two Ru atoms in 5a were not observed (Fig.…”

“…The μ-η 2 -coordination of pyridine-2-carbaldehyde- N -isopropylimine at a dinuclear site has been reported by Stufkens's and Vrieze's groups, 54–57 and the structural and spectral features of 7c quite resemble those of the μ-η 2 -dihydrobipyridine complex [(Cp*Ru) 2 (μ-η 2 -4,4′-Me 2 dhbpy)(μ-H)(H)] ( 7d ; dhbpy = dihydrobipyridine), which was obtained by the reaction of [Cp*Ru(μ-H) 4 RuCp*] with γ-picoline. 28…”