Design and Study of Bi[1,8]naphthyridine Ligands as Potential Photooxidation Mediators in Ru(II) Polypyridyl Aquo Complexes

Abstract

A series of 3,3'-polymethylene-bridged bi[1,8]naphthyridine (binap) ligands, 3a-c, are complexed with Ru(II) to afford [Ru(tpy)(3a-c)(H(2)O)](2+) where an uncomplexed nitrogen on 3a-c is situated so it can form a H-bond with the coordinated water. An additional complex involving [Ru(4'-NMe(2)tpy)(3b)(H(2)O)](2+) is also prepared. X-ray analyses of the [Ru(tpy)(3a,c)(H(2)O)](2+) complexes indicate well-organized H-bonds even when the binap is nonplanar. In an attempt to realize photooxidation, the effects of light, varying potential, and pH were examined. A Pourbaix diagram indicated that the oxidation potential decreased by approximately 0.5 V in the pH range of 1.9-11.6. The lowest-energy electronic absorption for the binap complexes involves the metal-to-ligand charge transfer to the binap ligand and is sensitive to ligand planarity. The absorbance shifted to a lower energy as the auxiliary ligand became a better donor (4'-NMe(2)tpy) or as the water was deprotonated. Acetonitrile was found to displace water most easily for the complex of 3c, where the ligand is the least planar. Despite promising features, photooxidation of the bound water was not observed.

Models for Proton-coupled Electron Transfer in Photosystem II

“…While this work was in progress, very similar compounds were reported by Thummel and coworkers, differing only in that the binapy ligands have a hydrocarbon strap between the two napy units (Zong et al 2004). The spectroscopic, structural, and electrochemical data for [Ru(H 2 O)(binapy)(trpy)] 2+ (see Experimental Section) are very close to those reported by Zong et al for the strapped analogs.…”

“…(a) Drawing of the partially refined, disordered cation in the X-ray structure of [Ru(H 2 O)(binapy)(trpy)](BPH 4 ) 2 (acetone) 2 (very similar to structures reported byZong et al 2004). (b) Drawing of the cation in the X-ray structure of [Ru(NCMe)(binapy)(trpy)](PF 6 ) 2 (MeCN) 2 .…”

Mechanisms and Factors Controlling Photoisomerization Equilibria, Ligand Exchange, and Water Oxidation Catalysis Capabilities of Mononuclear Ruthen­ium(II) Complexes

“…0.1 Å shorter than the other Ru-N distances in the tpy ligand, similarly to the case in [Ru(tpy)(bpy)Cl] + (bpy = 2,2Ј-bipyridine) [28][29][30] and [Ru(tpy)(bpy)OH 2 ] 2+ derivatives. [11,31,32,[33][34][35][36][37] [11,50,51,[52][53][54][55][56] owing to the steric repulsion between the aquo ligand and H28 on the quinoline moiety. 2+ derivatives, due to steric repulsion between H28 on the quinoline moiety and a tpy ligand.…”

New heteroaromatic polyazomethines containing naphthyridine moieties: Synthesis, characterization, and biological screening

“…1,8‐Naphthyridine and its derivatives have been of great interest for many people for the reason that they are potential bidentate ligands and have a broad spectrum of their biological activities 32–36. In recent years, more and more people have been interested in the development of multifunctional materials 37–39.…”