Ruthenium(II) Polypyridyl Complex with Phosphoric Acid As Anchoring Group: Synthesis, Characterization & Application

Ruthenium complexes containing phosphoric acid as anchoring group are well known as dyes for water splitting reactions when combined with TiO₂. A three-pot synthesis using 2,6-diacetylpyridine, n-octyloxybenzaldehyde, phenylhydrazine and lead (IV) tetraacetate yielded a Pyridine dipyrazolinel tridentate ligand (L3). The ligand L3 is well characterized by ¹H NMR. Reaction of ligand with RuCl₃.3H₂O yielded [RuCl₃.L3] (2), which was characterized by single-HR mass spec. The ruthenium (III) complex (2) is further reacted with tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate) to make [RuCl(L3).tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate)]Cl (3). The black dye [RuCl(L3).tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate.NCS]ClO₄ (4) is synthesized by reacting compound 3 with an excess of potassium thiocyanate followed by a metathesis reaction with LiClO₄ (aq). This new black dye was characterized by ESI MS, UV and emission spectroscopy and it needs to be hydrolyzed prior to test for water splitting reactions after thorough analytical characterization. Long alkyl chains adorn this new pyrazolyl ligand to limit solubility and promote stability of the ruthenium dye complexes in dye-sensitized solar cell applications.