Ru(ii) water oxidation catalysts with 2,3-bis(2-pyridyl)pyrazine and tris(pyrazolyl)methane ligands: assembly of photo-active and catalytically active subunits in a dinuclear structure

Abstract

A combined DFT and experimental study indicates that one water molecule is allowed to enter the first coordination sphere of a one-site catalyst, thus activating water oxidation.

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

“…The production of molecular oxygen with a large Ce IV excess and varying the catalyst concentration (Figure 6) suggests that for 1 the water nucleophilic attack is the dominant mechanism under the employed experimental conditions [17] …”

“…The oxidation behavior of the new compounds was first studied in acetonitrile solution. In this condition, 1 exhibits a reversible one‐electron oxidation, attributed to the oxidation of the metal center, at +1.16 V vs. SCE [17,27] . In 3 , two different metal environments are present, i. e. Ru P (Ru bound to bpy) and Ru C (Ru bound to tpm).…”

“…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).…”

“…Tris(1‐pyrazolyl)methane complexes have found various applications in catalysis, due to the peculiar features of the tpm moiety, such as its structural variability, donor‐atom set and denticity; [14] in particular, the facial configuration of tpm may offer the advantage of generating a complex wherein other ligands bind the metal center in an enforced facial geometry. Several mono‐ and dinuclear tpm‐based ruthenium(II) complexes have been reported, [15] however, this class of compounds has been sparingly investigated for the water oxidation catalytic behavior hitherto [16,17] …”

“…Several mono-and dinuclear tpm-based ruthenium (II) complexes have been reported, [15] however, this class of compounds has been sparingly investigated for the water oxidation catalytic behavior hitherto. [16,17] Recently, we described a synthetic and electro-catalytic study on Ru II -tpm complexes containing an additional 2,3-bis(2pyridyl)-pyrazine ligand (dpp), [17] which may work as a bridge connecting two metal frames in a dyad molecule (compounds I and II in Figure 1). [18] Experiments, in accordance with DFT results, suggest that the tpm ligand may play a key role in the water oxidation catalysis, by switching its coordination mode from tridentate to bidentate, thus accelerating the preliminary coordination of water to the ruthenium center.…”