Dinuclear Ru2 Research Articles

Large π‐Conjugated Chromophores Derived from Tetrathiafulvalene

AbstractA large π‐conjugated chromophore composed of two dipyrido[3,2‐a:2′,3′‐c]phenazine units directly fused to the central tetrathiafulvalene core has been prepared as a bridging ligand and its strong binding ability to Ru2+ to form a new dinuclear complex is presented. The electronic absorption and luminescence spectra and the electrochemical behavior of the free ligand and the Ru2+ complex have been investigated in detail. The free ligand shows a very strong band in the UV region consistent with ligand‐centered π–π* transitions and an intense broad band in the visible region that corresponds to an intramolecular charge‐transfer (ILCT) transition. Upon coordination, a metal‐to‐ligand charge‐transfer band appears at 22520 cm−1, and the ILCT band is bathochromically shifted by 1620 cm−1. These electrochemically amphoteric chromophores have also been characterized by spectro‐electrochemical methods. The oxidized radical species of the free ligand show a strong tendency to undergo aggregation, in which long‐distance attractive interactions overcome the electrostatic repulsion. Moreover, these two new chromophores reveal an ILCT fluorescence with large solvent‐dependent Stokes shifts and quantum efficiencies of 0.052 for the free ligand and 0.016 for its dinuclear Ru2+ complex in CH2Cl2.

Ru2(CO)4{OOC(CH2) n CH3}2L2 sawhorse-type complexes containing μ2-η2-carboxylato ligands derived from saturated fatty acids

The thermal reaction of Ru3(CO)12 with the saturated fatty acids (heptanoic, nonanoic, decanoic, tridecanoic, tetradecanoic, heptadecanoic, octadecanoic) in refluxing tetrahydrofuran, followed by addition of triphenylphosphine (PPh3) or pyridine (C5H5N), gives the dinuclear complexes Ru2(CO)4{OOC(CH2)nCH3}2L2 (1: n = 5, 2: n = 7, 3: n = 8, 4: n = 11, 5: n = 12, 6: n = 15, 7: n = 16; a: L = NC5H5, b: L = PPh3). The single crystal structure analysis of 1b, 2a, 3a, 4a and 5a reveals a dinuclear Ru2(CO)4 sawhorse structure, the diruthenium backbone being bridged by the carboxylato ligands, while the two L ligands occupy the axial positions at the ruthenium atoms. In 2a, π-π stacking interactions between adjacent pyridyl units of symmetry related molecules prevail, while in the longer alkyl chain derivatives 3a, 4a and 5a, additional van der Waals and electrostatic interactions between the alkyl chains take place as well in the packing arrangement of the molecules, thus giving rise to layers of parallel alkyl chains in the crystal.

New Dinuclear Ru2(CO)4 Sawhorse‐Type Complexes Containing Bridging Carboxylato Ligands

AbstractThe thermal reaction of Ru3(CO)12 with ethacrynic acid, 4‐[bis(2‐chlorethyl)amino]benzenebutanoic acid (chlorambucil), or 4‐phenylbutyric acid in refluxing solvents, followed by addition of two‐electron donor ligands (L), gives the diruthenium complexes Ru2(CO)4(O2CR)2L2 (1: R = CH2O‐C6H2Cl2‐COC(CH2)C2H5, L = C5H5N; 2: R = CH2O‐C6H2Cl2‐COC(CH2)C2H5, L = PPh3; 3: R = C3H6‐C6H4‐N(C2H4‐Cl)2, L = C5H5N; 4: R = C3H6‐C6H4‐N(C2H4‐Cl)2, L = PPh3; 5: R = C3H6‐C6H5, L = C5H5N; 6: R = C3H6‐C6H5, L = PPh3). The single‐crystal structure analyses of 2, 3, 5 and 6 reveal a dinuclear Ru2(CO)4 sawhorse structure, the diruthenium backbone being bridged by the carboxylato ligands, while the two L ligands occupy the axial positions of the diruthenium unit.

Synthesis and Characterization of Dinuclear Ruthenium Complexes Covalently Linked to RuII Tris‐bipyridine: An Approach to Mimics of the Donor Side of Photosystem II

To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these complexes, a mixed-valent dinuclear Ru2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru(II) tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru2(II,III) and Ru2(III,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)3]2+ photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bpy)3]2+ moiety to the conduction band of TiO2 followed by intramolecular electron transfer from the dinuclear Ru2(II,III) moiety to photogenerated Ru(III) was observed. The resulting long-lived Ru2(III,III) state decays on the millisecond timescale.

Reactivity of dinuclear arene ruthenium complexes: reactions of the hydrido complex [(p-Me-C6H4-Pri)2Ru2Cl2(μ-Cl)(μ-H)] with NaX and HX (X=F, Cl, Br, I)

The dinuclear hydrido complex [(p-Me-C6H4-Pri)2Ru2Cl2(μ-Cl)(μ-H)] (1) reacts with the sodium halides NaX in methanol to give the halogen analogues [(p-Me-C6H4-Pri)2Ru2X2(μ-X)(μ-H)] (2: X=F, 3: X=Br, 4: X=I). With HX, complex 1 reacts to give the tetrahalo complexes [(p-Me-C6H4-Pri)2Ru2X2(μ-X)2] (5: X=Cl, 6: X=Br, 7: X=I); in the case of X=I, a large excess of HI leads to the formation of the cationic complex [(p-Me-C6H4-Pri)2Ru2(μ-I)3]+ (8). The X-ray structure analysis of 1 shows a dinuclear Ru2 backbone with two terminal chloro ligands being trans with respect to each other as the two p-cymene ligands, the two bridging ligands lie in a plane perpendicular to the plane defined by the terminal chloro ligands and the ruthenium atoms.

Oxidation of the Sulfide Ligands to SO42-in the Dinuclear Complex {RuCl[P(OMe)3]2}2(μ-S2)(μ-Cl)(μ-N2H4): Synthesis and Characterization of {RuCl[P(OMe)3]2}2(μ-S2)(μ-Cl)(μ-N2H4)+HSO4-, {RuCl2[P(OMe)3]2}2(μ-S)(μ-N2H4), and {RuCl[P(OMe)3]2}2(μ-S2O5)(μ-N2H4)

The paramagnetic dinuclear Ru2+Ru3+ complex, {RuCl[P(OMe)3]2}2(μ-S2)(μ-Cl)(μ-N2H4) (1), reduces dioxygen by one-electron at room temperature in CH3CN to form 1+O2-, in which O2- is coordinated to the μ-S2 ligand. The dioxygen reduction is preceded by protonation to yield HO2+ by the bridging hydrazine ligand. Complex 1 is electrochemically more negative than HO2+, and a redox reaction generates 1+ and HO2 (→ O2- + H+). Spectroscopic studies (NMR and UV−vis) show that 1 and 1+O2- are under equilibrium, and the succeeding disproportionation reaction of 1+O2- produces two intermediates, 1+ and the dithionite complex, 1+(O2-)2, as an intermediate. The dithionite intermediate undergoes Cl- dissociation and further oxidation to yield the dinuclear Ru complex {Ru2+Cl[P(OMe)3]2}2(μ-S2O5)(μ-N2H4) (3). The liberated Cl- attacks the dithionite complex, and induces SO42- dissociation to prepare the dinuclear complex {Ru3+Cl2[P(OMe)3]2}2(μ-S)(μ-N2H4) (5). On the other hand, intermediate 1+ forms an ion pair with HSO4-...