Heteroleptic Ruthenium Research Articles

Biomimetic Models of the Photosynthetic Reaction Center Based on Ruthenium−Polypyridine Complexes

Mimicking the fundamental processes of the photosynthetic reaction center is a large field of research over the past decade. We present as biomimetic model systems for electron transfer the mono- and heteroleptic ruthenium complexes 2−9 containing differently substituted bipyridazine−glycol ligands. Depending on the number of glycol chains of the complexes 2−9, they are divided into three classes: A (2 branches, 2−4); B (3 branches, 5−6) and C (6 branches, 7−9). UV, fluorescence, single-photon counting, and laser flash photolysis were employed as techniques for photophysical characterization. Redox properties were determined using cyclic voltammetry. Detailed steady-state quenching studies of 2−9 with MV2+, OV2+, and MPVS have shown different supramolecular interactions between sensitizer and acceptor in the case of MV2+. These effects may be explained by π−π donor−acceptor attractions as well as hydrophobic interactions. Supporting molecular modeling studies have been done. The suitability as biomimetic model systems was shown by testing the ruthenium complexes 2−9 in artificial photosynthesis systems. Two typical reactions were selected: the sacrificial reduction of water and the reduction of CO2 to CH4. The use of 2−9 leads to satisfactory hydrogen production from the reduction of water. In the CH4/CO2 system, complexes 7−9 worked efficiently.

Syntheses, electrochemistry and electrodeposition of ruthenium(II) complexes of 4,4′-bis(4-anilinovinyl)-2,2′-bipyridine

The synthesis of a new disubstituted bipyridine ligand, 4,4′-bis(4-anilinovinyl)-2,2′-bipyridine (L 2), and its homoleptic and heteroleptic ruthenium(II) complexes [RuL 3 2] 2+ and [RuL 2(bpy) 2] 2+ are described. Both complexes undergo electrochemical polymerization in acetonitrile. [RuL 2(bpy) 2] 2+ produced a conducting but non-robust polymer film, while [RuL 3 2] 2+ produced an insulating film.

Preparation of New Octopus Shaped Homoleptic and Heteroleptic Ruthenium(II)-Bisdiazine Complexes

The preparation of RuL3 (1), RuL2L’ (2) and Ru(pod) (3) complexes containing polyethylene glycol chains is described. The complexes are further functionalized by 4-oxyanisyl or by hydrophilic hydroxyl groups. These new complexes may interact in supramolecular assemblies with suitable acceptors such as mono- and bisviologens to form biomimetic models for photosynthesis.

Metallosupramolecular complexes containing ferrocenyl groups as redox spectators; synthesis and co-ordination behaviour of the helicand 4′,4‴-bis(ferrocenyl)2,2′ : 6′,2″ : 6″,2‴ : 6‴,2â�—-quinquepyridine

The compound 4′,4‴-bis(ferrocenyl)-2,2′ : 6′,2″ : 6″,2‴ : 6‴ : 2â�—-quinquepyridine (L) has been prepared in two steps from ferrocenecarbaldehyde and 2,6-diacetylpyridine and its co-ordination behaviour investigated. Reaction with cobalt(II) and iron(II) salts gives the seven-co-ordinate complexes [ML(H2O)2][PF6]2(M = Co or Fe). The presence of ferrocenyl groups in the ligand appears not to present a steric barrier to the formation of helicates, and the double-helical complexes [Ni2L2(H2O)2][PF6]4, and [Cu2L2][PF6]3 can be obtained by reaction with nickel(II) and copper(II) salts respectively. The compound L reacts with [RuCl3L′](L′= 2,2′ : 6′,2″-terpyridine or its 4′-dimethylamino, -methylsulfonyl or -ferrocenyl derivatives) to give the heteroleptic ruthenium(II) complexes [RuL(L′)][PF6]2. In these complexes L is acting as a tridentate hypodentate ligand leaving a non-co-ordinated didentate 2,2′-bipyridyl moiety. The latter may act as a didentate domain for an additional ruthenium centre, and the tetranuclear complexes [L′RuLRuCl(L′)][PF6]3 with two ruthenium(II) centres in two different, N6 and N5Cl, donor environments have been prepared.

LIGAND‐DEPENDENT INTERACTION OF RUTHENIUM(II) POLYPYRIDYL COMPLEXES WITH DNA PROBED BY EMISSION SPECTROSCOPY

The nature of the interaction in buffered aqueous solution of several homo and heteroleptic ruthenium(II) polypyridyl complexes containing 2,2'-bipyridine (bpy), 2,2'-bipyrazine (bpz), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dip), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), 1,4,5,8-tetraazaphenanthrene (tap), and 1,4,5,8,9,12-hexaazatriphenylene (hat) with calf thymus DNA and poly(dA-dT).poly(dA-dT) (pdAT) has been investigated by steady-state spectroscopy and emission lifetime measurements. Those complexes containing two or more tap/hat ligands photo-oxidize the guanine base upon binding to DNA with efficiencies that parallel their excited state redox potentials, but display "normal" behavior (increase of both the emission intensity and lifetime) when bound to pdAT. However Ru(tap)(hat)2+2 and Ru(hat)2+3 even photooxidize the adenine base of pdAT, so that their excited states are also quenched in the presence of either polynucleotide. The electron transfer quenching mechanism has been confirmed previously by detection of the monoreduced complex in laser flash photolysis experiments in the presence of mononucleotides. Most of the complexes investigated appear to bind to DNA, at least in part via intercalation, with affinities being dependent on the nature of the largest ligand (hat shows the highest ability in heteroleptic complexes). From lifetime quenching experiments, in the presence of moderate amounts of NaCl, surface binding does not appear to be a general mode for the complexes investigated, and it has been demonstrated unequivocally only for Ru(phen)2+3. In addition, the intercalation of complexes into DNA increases as the ionic strength of the medium decreases, the DNA/Ru ratio increases, or when water is partially replaced by glycerol.

Synthesis, spectroscopy, and electrochemistry of homo- and hetero-leptic ruthenium(II) complexes of new pyrazole-containing bidentate ligands

Heteroleptic [Ru(bipy)2(L–L′)]2+ and homoleptic [Ru(L–L′)3]2+ complexes, where bipy = 2,2′-bipyridine and L–L′ is one of nine new pyrazole-containing bidentate ligands, have been prepared. Full assignments have been made for the 1H and 13C n.m.r. spectra of the complexes in CD3CN and the origins of the co-ordination-induced shifts are discussed. The absorption spectra and redox properties of the complexes are also discussed.