Dinuclear Tris(1‐pyrazolyl)methane Complexes of Ruthenium(II)

Abstract

By exploiting the “complexes‐as‐metals/complexes‐as‐ligands” synthetic strategy, six new dinuclear achiral complexes of RuII, containing the tripodal ligand tris(1‐pyrazolyl)methane (tpm), a chelating ligand (L‐L) such as 2,2′‐bipyridine (2,2′‐bpy), 1,10‐phenanthroline (phen) or 2,2′‐biquinoline (biq), and either pyrazine (pz) or 4,4′‐bipyridine (4,4′‐bpy) as bridging ligands (BL), have been prepared and fully characterized. The starting building blocks, many of which have been synthesized for the first time, have been conveniently prepared by improved literature methods. The reactivity of these building blocks in specific experimental conditions has been rationalized. All novel compounds have been characterized fully by elemental analysis and FT‐IR. 1H NMR spectra have been carefully assigned and interpreted on the basis of possible inductive and magnetic anisotropic effects exerted by the ligands. Electrochemical, UV/Vis spectroscopic, and luminescence studies have been carried out on all the dinuclear complexes and their precursor species; the collected data have been discussed and thoroughly interpreted. RuII/RuIII mixed‐valence species of two dinuclear compounds have been investigated by spectroelectrochemistry and assigned to the Robin and Day's Class II group on the basis of the experimental parameters obtained.

Reactivity of Tris(1‐pyrazolyl)methane Towards Ru0 Complexes

“…Note that in complex 4 the H d proton resonates at δ = 9.72 ppm in CDCl 3 solution (Table 1), an increase of 1.29 ppm compared with free tpm in the same solvent, which accounts for the very different inductive effect exerted by a chlorido ligand with respect to a hydrido ligand and also confirms that such effects on the benzyl-like position are particularly efficient, because they are mediated by three aromatic rings. [2] The cod signals in the 1 H and 13 C NMR spectra of 3 (Table 1, Figure 2) indicate a totally asymmetric environment for this ligand. In fact, four multiplets and four different resonances are observed in the 1 H and 13 C NMR spectra, respectively, which can be ascribed to four inequivalent olefinic protons and carbon atoms in cod.…”

“…The apical tpm hydrogen atom (H d in Scheme 3) appears only slightly deshielded with respect to the free ligand (δ = 9.20 vs. 8.93 ppm in [D 6 ]DMSO solution) in spite of the high hydrogen-bonding ability of DMSO, which in coordinated tpm can result in a deshielding effect of more than 1.5 ppm. [2] Most likely the formal negative charge on the ligand (also revealed by the low chemical shift values of H aЈЈ and H bЈЈ ) strongly reduces the hydrogen-bonding ability of the tpm methine group. Note that in complex 4 the H d proton resonates at δ = 9.72 ppm in CDCl 3 solution (Table 1), an increase of 1.29 ppm compared with free tpm in the same solvent, which accounts for the very different inductive effect exerted by a chlorido ligand with respect to a hydrido ligand and also confirms that such effects on the benzyl-like position are particularly efficient, because they are mediated by three aromatic rings.…”

“…4+ (L-L = 2,2Ј-bipyridine, 1,10-phenanthroline, 2,2Ј-biquinoline; BL = pyrazine, 4,4Ј-bipyridine) [2] obtained from suitable mononuclear synthons by exploiting the "complexes-as-metals/complexes-as-ligands" synthetic strategy. [3] Within this framework, and aiming at novel Ru synthons, we decided to test the reactivity of tpm towards Ru 0 species, a topic not reported in the literature.…”

Unsymmetrical Dinuclear RuII Complexes with Bridging Polydentate Nitrogen Ligands as Potential Water Oxidation Catalysts

“…Organic reactants (Merck or TCI Europe) and RuCl 3 ⋅ 3H 2 O (Strem) were commercial products of the highest purity available. Tris(pyrazolyl)methane (tpm), [15j] 2,3‐bis(2‐pyridyl)pyrazine (dpp), [17] 3,6‐bis‐(2‐pyridyl)‐1,2,4,5‐tetrazine (bptz),28 [RuCl 3 (tpm)], [15f] cis ‐[RuCl 2 (bipy) 2 ] (bipy=2,2′‐bipyridine),29 cis ‐[RuCl 2 (bqn) 2 ] (bqn=2,2’‐biquinoline),30 [RuCl 2 (η 6 ‐ p ‐cymene)] 2 ,31 and [2]BF 4 [20] were prepared according to the respective literature methods. Chromatographic separations were carried out on columns of silica (Merck, Ø=0.05–0.20 mm).…”