The synthesis and structure of heteroleptic tris(diimine)ruthenium(II) complexes

The reactions of bidentate diimine ligands (L2) with cationic bis(diimine)[Ru(L)(L1)(CO)Cl]+ complexes (L, L1, L2 are dissimilar diimine ligands), in the presence of trimethylamine-N-oxide (Me3NO) as a decarbonylation reagent, lead to the formation of heteroleptic tris(diimine) ruthenium(II) complexes, [Ru(L)(L1)(L2)]2+. Typically isolated as hexafluorophosphate or perchlorate salts, these complexes were characterised by UV-visible, infrared and mass spectroscopy, cyclic voltammetry, microanalyses and NMR spectroscopy. Single crystal X-ray studies have elucidated the structures of K[Ru(bpy)(phen)(4,4'-Me(2)bpy)](PF(6))(3).1/2H(2)O, [Ru(bpy)(5,6-Me(2)phen)(Hdpa)](ClO(4))(2), [Ru(bpy)(phen)(5,6-Me(2)phen)](ClO(4))(2), [Ru(bpy)(5,6'-Me(2)phen)(4,4'-Me(2)bpy)](PF(6))(2).EtOH, [Ru(4,4'-Me(2)bpy)(phen)(Hdpa)](PF(6))(2).MeOH and [Ru(bpy)(4,4'-Me(2)bpy)(Hdpa)](ClO(4))(2).1/2Hdpa (where Hdpa is di(2-pyridyl)amine). A novel feature of the first complex is the presence of a dinuclear anionic adduct, [K(2)(PF(6))(6)](4-), in which the two potassium centres are bridged by two fluorides from different hexafluorophosphate ions forming a K(2)F(2) bridging unit and by two KFPFK bridging moieties.     

Synthesis of mononuclear and dinuclear ruthenium(II) tris(heteroleptic) complexes via photosubstitution in bis(carbonyl) precursors

A novel, and quite general, approach for the preparation of tris(heteroleptic) ruthenium(II) complexes is reported. Using this method, which is based on photosubstitution of carbonyl ligands in precursors such as [Ru(bpy)(CO)(2)Cl(2)] and [Ru(bpy)(Me(2)bpy)(CO)(2)](PF(6))(2), mononuclear and dinuclear Ru(II) tris(heteroleptic) polypyridyl complexes containing the bridging ligands 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) and 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (Hbpzt) have been prepared. The complexes obtained were purified by column chromatography and characterized by HPLC, mass spectrometry, 1H NMR, absorption and emission spectroscopy and by electrochemical methods. The X-ray structures of the compounds [Ru(bpy)(Me(2)bpy)(bpt)](PF(6))x0.5C(4)H(10)O [1x0.5C(4)H(10)O], [Ru(bpy)(Me(2)bpy)(bpzt)](PF(6))xH(2)O (2xH(2)O) and [Ru(bpy)(Me(2)bpy)(CH(3)CN)(2)](PF(6))(2)xC(4)H(10)O (6xC(4)H(10)O) are reported. The synthesis and characterisation of the dinuclear analogues of 1 and 2, [{Ru(bpy)(Me(2)bpy)}(2)bpt](PF(6))(3)x2H(2)O (3) and [{Ru(bpy)(Me(2)bpy)}(2)bpzt](PF(6))(3) (4), are also described.     

Ruthenium(II)-polyazine light absorbers bridged to reactive cis-dichlororhodium(III) centers in a bimetallic molecular architecture

Bimetallic complexes of the form [(bpy)(2)Ru(BL)RhCl(2)(phen)](PF(6))(3), where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and BL = 2,3-bis(2-pyridyl)pyrazine (dpp) or 2,2'-bipyrimidine (bpm), were synthesized, characterized, and compared to the [{(bpy)(2)Ru(BL)}(2)RhCl(2)](PF(6))(5) trimetallic analogues. The new complexes were synthesized via the building block method, exploiting the known coordination chemistry of Rh(III) polyazine complexes. In contrast to [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) and [{(bpy)(2)Ru(bpm)}(2)RhCl(2)](PF(6))(5), [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) have a single visible light absorber subunit coupled to the cis-Rh(III)Cl(2) moiety, an unexplored molecular architecture. The electrochemistry of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) showed a reversible oxidation at 1.61 V (vs Ag/AgCl) (Ru(III/II)), quasi-reversible reductions at -0.39 V, -0.74, and -0.98 V. The first two reductive couples corresponded to two electrons, consistent with Rh reduction. The electrochemistry of [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) exhibited a reversible oxidation at 1.76 V (Ru(III/II)). A reversible reduction at -0.14 V (bpm(0/-)), and quasi-reversible reductions at -0.77 and -0.91 V each corresponded to a one electron process, bpm(0/-), Rh(III/II), and Rh(II/I). The dpp bridged bimetallic and trimetallic display Ru(dpi)-->dpp(pi*) metal-to-ligand charge transfer (MLCT) transitions at 509 nm (14,700 M(-1) cm(-1)) and 518 nm (26,100 M(-1) cm(-1)), respectively. The bpm bridged bimetallic and trimetallic display Ru(dpi)-->bpm(pi*) charge transfer (CT) transitions at 581 nm (4,000 M(-1) cm(-1)) and 594 nm (9,900 M(-1) cm(-1)), respectively. The heteronuclear complexes [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) had (3)MLCT emissions that are Ru(dpi)-->dpp(pi*) CT in nature but were red-shifted and lower intensity than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4). The lifetimes of the (3)MLCT state of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) at room temperature (30 ns) was shorter than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4), consistent with favorable electron transfer to Rh(III) to generate a metal-to-metal charge-transfer ((3)MMCT) state. The reported synthetic methods provide means to a new molecular architecture coupling a single Ru light absorber to the Rh(III) center while retaining the interesting cis-Rh(III)Cl(2) moiety.     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

Synthesis of ruthenium(II) complexes of tetradentate bis(N-pyridylimidazolylidenyl)methane and their reactivities towards N- donors

A family of hexa-coordinated ruthenium(II) complexes of bis(N-pyridylimidazolylidenyl)methane (L) were prepared and structurally characterized. Carbene transfer reactions of [Ru(p-cymene)Cl(2)](2), [Ru(CO)(2)Cl(2)](n) and RuHCl(CO)(PPh(3))(3) with silver-NHC complexes in situ generated from [H(2)L](PF(6))(2) and Ag(2)O afforded [RuL(CH(3)CN)(2)](PF(6))(2) (1), [Ru(2)L(p-cymene)(2)Cl(2)](PF(6))(2) (2), [RuL(CO)(2)](PF(6))(2) (3) and [RuL(PPh(3))(2)](PF(6))(2) (4), respectively. The reactions of 1 towards several N- and P-donors were studied. The treatment of 1 with 1,10-phenanthroline resulted in the substitution of one pyridine and one acetonitrile molecule affording [RuL(phen)(CH(3)CN)](PF(6))(2) (5) as a mixture of two isomers. Reaction of 1,2-bis(diphenylphosphino)ethane (dppe) and 1 gave [RuL(dppe)(CH(3)CN)(2)](PF(6))(2) (7), in which two pyridines were substituted by a dppe ligand trans to two NHC groups. In contrast, reactions of 1 with ethane-1,2-diamine, propane-1,3-diamine and 3,5-dimethyl-1H-pyrazole led to the substitution of acetonitrile and subsequent N-H addition of the C≡N bond of the coordinated acetonitrile yielding [RuL(ethane-1,2-diamine)(N-(2-aminoethyl)acetimidamide)](PF(6))(2) (8), [RuL(propane-1,3-diamine)(N-(3-aminopropyl)acetimidamide)](PF(6))(2) (9) and RuL(1-(3,5-dimethyl-1H-pyrazol-1-yl)ethanimine)(CH(3)CN)](PF(6))(2) (10), respectively.     

Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes

We report the synthesis of free 1,6,7,12-tetraazaperylene (tape). Tape was obtained from 1,1'-bis-2,7-naphthyridine by potassium promoted cyclization followed by oxidation with air. Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes of the general formulas [Ru(L-L)(2)(tape)](PF(6))(2), [1](PF(6))(2)-[5](PF(6))(2), and [{Ru(L-L)(2)}(2)(μ-tape)](PF(6))(4), [6](PF(6))(4)-[10](PF(6))(4), with{L-L = phen, bpy, dmbpy (4,4'-dimethyl-2,2'-bipyridine), dtbbpy (4,4'-ditertbutyl-2,2'-bipyridine) and tmbpy (4,4'5,5'-tetramethyl-2,2'-bipyridine)}, respectively, were synthesized. The X-ray structures of tape·2CHCl(3) and the mononuclear complexes [Ru(bpy)(2)(tape)](PF(6))(2)·0.5CH(3)CN·0.5toluene, [Ru(dmbpy)(2)(tape)](PF(6))(2)·2toluene and [Ru(dtbbpy)(2)(tape)](PF(6))(2)·3acetone·0.5H(2)O were solved. The UV-vis absorption spectra and the electrochemical behavior of the ruthenium(ii) tape complexes were explored and compared with the data of the analogous dibenzoeilatin (dbneil), 2,2'-bipyrimidine (bpym) and tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazin (tpphz) species.     

Scrutinizing low-spin Cr(II) complexes

The oxidation state of the chromium center in the following compounds has been probed using a combination of chromium K-edge X-ray absorption spectroscopy and density functional theory: [Cr(phen)(3)][PF(6)](2) (1), [Cr(phen)(3)][PF(6)](3) (2), [CrCl(2)((t)bpy)(2)] (3), [CrCl(2)(bpy)(2)]Cl(0.38)[PF(6)](0.62) (4), [Cr(TPP)(py)(2)] (5), [Cr((t)BuNC)(6)][PF(6)](2) (6), [CrCl(2)(dmpe)(2)] (7), and [Cr(Cp)(2)] (8), where phen is 1,10-phenanthroline, (t)bpy is 4,4'-di-tert-butyl-2,2'-bipyridine, and TPP(2-) is doubly deprotonated 5,10,15,20-tetraphenylporphyrin. The X-ray crystal structures of complexes 1, [Cr(phen)(3)][OTf](2) (1'), and 3 are reported. The X-ray absorption and computational data reveal that complexes 1-5 all contain a central Cr(III) ion (S(Cr) = (3)/(2)), whereas complexes 6-8 contain a central low-spin (S = 1) Cr(II) ion. Therefore, the electronic structures of 1-8 are best described as [Cr(III)(phen(?))(phen(0))(2)][PF(6)](2), [Cr(III)(phen(0))(3)][PF(6)](3), [Cr(III)Cl(2)((t)bpy(?))((t)bpy(0))], [Cr(III)Cl(2)(bpy(0))(2)]Cl(0.38)[PF(6)](0.62), [Cr(III)(TPP(3?-))(py)(2)], [Cr(II)((t)BuNC)(6)][PF(6)](2), [Cr(II)Cl(2)(dmpe)(2)], and [Cr(II)(Cp)(2)], respectively, where (L(0)) and (L(?))(-) (L = phen, (t)bpy, or bpy) are the diamagnetic neutral and one-electron-reduced radical monoanionic forms of L, and TPP(3?-) is the one-electron-reduced doublet form of diamagnetic TPP(2-). Following our previous results that have shown [Cr((t)bpy)(3)](2+) and [Cr(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine) to contain a central Cr(III) ion, the current results further refine the scope of compounds that may be described as low-spin Cr(II) and reveal that this is a very rare oxidation state accessible only with ligands in the strong-field extreme of the spectrochemical series.     

Synthesis, structures, and properties of ruthenium(II) complexes of N-(1,10-phenanthrolin-2-yl)imidazolylidenes

Mononuclear ruthenium complexes [RuCl(L1)(CH(3)CN)(2)](PF(6)) (2a), [RuCl(L2)(CH(3)CN)(2)](PF(6)) (2b), [Ru(L1)(CH(3)CN)(3)](PF(6))(2) (4a), [Ru(L2)(CH(3)CN)(3)](PF(6))(2) (4b), [Ru(L2)(2)](PF(6))(2) (5), [RuCl(L1)(CH(3)CN)(PPh(3))](PF(6)) (6), [RuCl(L1)(CO)(2)](PF(6)) (7), and [RuCl(L1)(CO)(PPh(3))](PF(6)) (8), and a tetranuclear complex [Ru(2)Ag(2)Cl(2)(L1)(2)(CH(3)CN)(6)](PF(6))(4) (3) containing 3-(1,10-phenanthrolin-2-yl)-1-(pyridin-2-ylmethyl)imidazolylidene (L1) and 3-butyl-1-(1,10-phenanthrolin-2-yl)imidazolylidene (L2) have been prepared and fully characterized by NMR, ESI-MS, UV-vis spectroscopy, and X-ray crystallography. Both L1 and L2 act as pincer NNC donors coordinated to ruthenium (II) ion. In 3, the Ru(II) and Ag(I) ions are linked by two bridging Cl(-) through a rhomboid Ag(2)Cl(2) ring with two Ru(II) extending to above and down the plane. Complexes 2-8 show absorption maximum over the 354-428 nm blueshifted compared to Ru(bpy)(3)(2+) due to strong σ-donating and weak π-acceptor properties of NHC ligands. Electrochemical studies show Ru(II)/Ru(III) couples over 0.578-1.274 V.     

Carbonyl-carboxylato-ruthenium complexes incorporating diimine ligands and unexpected cyclometalation of carboxylate ligands

We report two new synthetic routes to the dinuclear Ru(I) complexes, [Ru(I)(2)(RCO(2))(CO)(4)(N( wedge )N)(2)](+) (N( wedge )N = 2,2'-bipyridine or 1,10-phenanthroline derivatives) that use RuCl(3).3H(2)O as a starting material. Direct addition of the bidentate diimine ligand to a methanolic solution of [Ru(CO)(2)Cl(2)](n) and sodium acetate yielded a mixture of [Ru(I)(2)(MeCO(2))(CO)(4)(N( wedge )N)(2)](+) (N( wedge )N = 4,4'-dmbpy, and 5,6-dmphen), and [Ru(II)(MeCO(2))(2)(CO)(2)(N( wedge )N)] (N( wedge )N = 4,4'-dmbpy and 5,5'-dmbpy). Single-crystal X-ray studies confirmed that the Ru(II) complexes had a trans-acetate-cis-carbonyl arrangement of the ligands. In contrast, the use of sodium benzoate resulted in the unexpected formation of a Ru-C bond producing ortho-cyclometalated complexes, [Ru(II)(O(2)CC(6)H(4))(CO)(2)(N( wedge )N)], where N( wedge )N = bpy or phen. A second approach used ligand exchange between a bidentate ligand (N( wedge )N) and the pyridine ligands of [Ru(I)(RCO(2))(CO)(2)(py)](2) to convert these neutral complexes into [Ru(I)(2)(RCO(2))(CO)(4)(N( wedge )N)(2)](+). This method, although it involved more steps, was applicable for a wider variety of diimine ligands (R = Me and N( wedge )N = 4,4'-dmbpy, 5,5'-dmbpy, 5,6-dmphen; R = Ph and N( wedge )N = bpy, phen, 5,6-dmphen).     

Monometallic and dimetallic ruthenium(II)-terpyridine complexes employing the tetradentate ligands dipyridylpyrazolyl,dipyridyloxadiazole, and their dimethyl derivatives

The tetradentate ligands, 2,2'-(1H-pyrazole-3,5-diyl)bis(4- methylpyridine) (4,4'-Me2dppzH), 2,2'-(1H-pyrazole-3,5-diyl)bis(6-methylpyridine) (6,6'-Me2dppzH), 3,5-di(pyrid-2-yl)pyrazole (dppzH), and dipyridyloxadiazole (dpo) react with either Ru(trpy)Cl3 or trans-Ru(trpy)Cl2(NCCH3), where trpy is 2,2',2'-terpyridine, to form a variety of Ru(II) complexes. Among these are the symmetrical chloro-bridged Ru(II) dimer and the "in" and "out" geometric isomers of the monometallic Ru(II) containing species where "in" and "out" refer to the orientation of the Ru-Cl vector relative to the centroid of the ligand backbone. Thirteen complexes were prepared and painstakingly purified by careful recrystallization and/or exhaustive column chromatography. These complexes were characterized by 1H and 13C NMR, electronic absorption, and infrared spectroscopy. Additionally, [Ru2(tryp)2(6,6'-Me2dppz)mu-Cl](BF4)2 (3b(BF4)2), [Ru2(trpy)2(4,4'-Me2dppz)mu-Cl](PF6)2.0.5MeOH (3c), [Ru2(trpy)2(6,6'-Me2dppz)(CH2C(O)CH3)](PF6)2.0.5(CH3)2CO (9b), "in"-[Ru(trpy)(4,4'-Me2dppz)Cl](PF6).(CH3)2CO (1c), and "out"-[Ru(trpy)(dpo)Cl](PF6).(CH3)2CO (2d) were characterized by X-ray crystallography. Several ligand substitution reactions were attempted. For example, [Ru2(trpy)2(6,6'-Me2dppz)mu-Cl](BF4)2 (3b) was reacted with hydroxide ion to produce [Ru2(trpy)2(6,6'-Me2dppz)mu-OH](PF6)2 (6b). Complex 6b reacts with benzyl bromide to produce [Ru2(trpy)2(6,6'-Me2dppz)mu-Br](PF6)2 (7b) or with (CH3)3Sil to produce [Ru2(trpy)2(6,6'-Me2dppz)mu-I](PF6)2 (8b). of 6b with acetone forms the methyl enolate complex [Ru2(trpy)2(6,6'-Me2dppz)(CH2COCH3)](PF6)2 (9b) while, analogously to a Cannizarro reaction, the reaction with benzaldehyde forms the bridging benzoate complex [Ru2(trpy)2(6,6'-Me2dppz)(C6H4CO2)](PF6)2 (11b). The bridging azide complex [Ru2(trpy)2(6,6'-Me2dppz)mu-N3](PF6)2 (10b) is formed by reaction of 6b with (CH3)3-SiN3. Additionally, the chloride ligands of the monometallic complexes of "in"-[Ru(trpy)(dpo)Cl](PF6) (1d), "in"-[Ru(trpy)(4,4'-Me2dpo)Cl](PF6)] (1e), and "out"-[Ru(trpy)(dpo)Cl](PF6) (2d) were substituted with water to form their respective aqua complexes, 4d, 4e, and 5d. All of the complexes exhibit broad unsymmetrial absorption bands in the visible portion of the electromagnetic spectrum. The dimetallic complexes 3b and 3c exhibit two, 1e- reversible oxidation waves at +0.72 and +1.15 V, and at +0.64 and +1.13 V, respectively. These complexes were not emissive.     

X-ray Crystallographic Study of the Ruthenium Blue Complexes [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2): Steric Interactions and the Ru-Ru "Bond Length"

X-ray crystal structures are reported for the following complexes: [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O (tacn = 1,4,7-triazacyclononane), monoclinic P2(1)/n, Z = 4, a = 14.418(8) ?, b = 11.577(3) ?, c = 18.471(1) ?, beta = 91.08(5) degrees, V = 3082 ?(3), R(R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) ?, b = 12.283(4) ?, c = 18.679(6) ?, beta = 109.19(2) degrees, V = 3069.5 ?(3), R(R(w)) = 0.052 (0.054) using 3668 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)I(3)(tacn)(2)](PF(6))(2), cubic P2(1)/3, Z = 3, a = 14.03(4) ?, beta = 90.0 degrees, V = 2763.1(1) ?(3), R (R(w)) = 0.022 (0.025) using 896 unique data with I > 2.5sigma(I) at 293 K. All of the cations have cofacial bioctahedral geometries, although [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2) are not isomorphous. Average bond lengths and angles for the cofacial bioctahedral cores, [N(3)Ru(&mgr;-X)(3)RuN(3)](2+), are compared to those for the analogous ammine complexes [Ru(2)Cl(3)(NH(3))(6)](BPh(4))(2) and [Ru(2)Br(3)(NH(3))(6)](ZnBr(4)). The Ru-Ru distances in the tacn complexes are longer than those in the equivalent ammine complexes, probably as a result of steric interactions.     

Comparative Study of C(∧)N and N(∧)C Type Cyclometalated Ruthenium Complexes with a NAD(+)/NADH Function

Cyclometalated ruthenium complexes having C(∧)N and N(∧)C type coordinating ligands with NAD(+)/NADH function have been synthesized and characterized by spectroscopic methods. The variation of the coordinating position of σ-donating carbon atom leads to a drastic change in their properties. Both the complex Ru(phbn)(phen)(2)]PF(6) ([1]PF(6)) and [Ru(pad)(phen)(2)]PF(6) ([2]PF(6)) reduced to Ru(phbnHH)(phen)(2)]PF(6) ([1HH]PF(6)) and [Ru(padHH)(phen)(2)]PF(6) ([2HH]PF(6)) by chemical and electrochemical methods. Complex [1]PF(6) photochemically reduced to [1HH]PF(6) in the presence of the sacrificial agent triethylamine (TEA) upon irradiation of visible light (λ ≥ 420 nm), whereas photochemical reduction of [2]PF(6) was not successful. Both experimental results and theoretical calculations reveal that upon protonation the energy level of the π* orbital of either of the ligands phbn or pad is drastically stabilized compared to the nonprotonated forms. In the protonated complex [Ru(padH)(phen)(2)](PF(6))(2) {[2H](PF(6))(2)}, the Ru-C bond exists in a tautomeric equilibrium with Ru═C coordination and behaves as a remote N-heterocyclic carbene (rNHC) compex; on the contrary, this behavior could not be observed in protonated complex [Ru(phbnH)(phen)(2)](PF(6))(2) {[1H](PF(6))(2)}.     

Coordination and Redox Chemistry of Substituted-Polypyridyl Complexes of Ruthenium

The complexes [Ru(tpy)(acac)(Cl)], [Ru(tpy)(acac)(H(2)O)](PF(6)) (tpy = 2,2',2"-terpyridine, acacH = 2,4 pentanedione) [Ru(tpy)(C(2)O(4))(H(2)O)] (C(2)O(4)(2)(-) = oxalato dianion), [Ru(tpy)(dppene)(Cl)](PF(6)) (dppene = cis-1,2-bis(diphenylphosphino)ethylene), [Ru(tpy)(dppene)(H(2)O)](PF(6))(2), [Ru(tpy)(C(2)O(4))(py)], [Ru(tpy)(acac)(py)](ClO(4)), [Ru(tpy)(acac)(NO(2))], [Ru(tpy)(acac)(NO)](PF(6))(2), and [Ru(tpy)(PSCS)Cl] (PSCS = 1-pyrrolidinedithiocarbamate anion) have been prepared and characterized by cyclic voltammetry and UV-visible and FTIR spectroscopy. [Ru(tpy)(acac)(NO(2))](+) is stable with respect to oxidation of coordinated NO(2)(-) on the cyclic voltammetric time scale. The nitrosyl [Ru(tpy)(acac)(NO)](2+) falls on an earlier correlation between nu(NO) (1914 cm(-)(1) in KBr) and E(1/2) for the first nitrosyl-based reduction 0.02 V vs SSCE. Oxalate ligand is lost from [Ru(II)(tpy)(C(2)O(4))(H(2)O)] to give [Ru(tpy)(H(2)O)(3)](2+). The Ru(III/II) and Ru(IV/III) couples of the aqua complexes are pH dependent. At pH 7.0, E(1/2) values are 0.43 V vs NHE for [Ru(III)(tpy)(acac)(OH)](+)/[Ru(II)(tpy)(acac)(H(2)O)](+), 0.80 V for [Ru(IV)(tpy)(acac)(O)](+)/[Ru(III)(tpy)(acac)(OH)](+), 0.16 V for [Ru(III)(tpy)(C(2)O(4))(OH)]/[Ru(II)(tpy)(C(2)O(4))(H(2)O)], and 0.45 V for [Ru(IV)(tpy)(C(2)O(4))(O)]/[Ru(III)(tpy)(C(2)O(4))(OH)]. Plots of E(1/2) vs pH define regions of stability for the various oxidation states and the pK(a) values of aqua and hydroxo forms. These measurements reveal that C(2)O(4)(2)(-) and acac(-) are electron donating to Ru(III) relative to bpy. Comparisons with redox potentials for 21 related polypyridyl couples reveal the influence of ligand changes on the potentials of the Ru(IV/III) and Ru(III/II) couples and the difference between them, DeltaE(1/2). The majority of the effect appears in the Ru(III/II) couple. ()A linear correlation exists between DeltaE(1/2) and the sum of a set of ligand parameters defined by Lever et al., SigmaE(i)(L(i)), for the series of complexes, but there is a dramatic change in slope at DeltaE(1/2) approximately -0.11 V and SigmaE(i)(L(i)) = 1.06 V. Extrapolation of the plot of DeltaE(1/2) vs SigmaE(i)(L(i)) suggests that there may be ligand environments in which Ru(III) is unstable with respect to disproportionation into Ru(IV) and Ru(II). This would make the two-electron Ru(IV)O/Ru(II)OH(2) couple more strongly oxidizing than the one-electron Ru(IV)O/Ru(III)OH couple.     

Coordination of 9-ethylguanine to the mixed-ligand compound alpha-[Ru(azpy)(bpy)Cl2] (azpy = 2-phenylazopyridine and bpy = 2,2'-bipyridine). An unprecedented ligand positional shift, correlated to the cytotoxicity of this type of [RuL2Cl2] (with L = azpy or bpy) complex

The striking difference in cytotoxic activity between the inactive cis-[Ru(bpy)(2)Cl(2)] and the recently reported highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha indicating the isomer in which the coordinating Cl atoms, pyridine nitrogens, and azo nitrogens are in mutual cis, trans, cis orientation) encouraged the synthesis of the mixed-ligand compound cis-[Ru(azpy)(bpy)Cl(2)]. The synthesis and characterization of the only occurring isomer, i.e., alpha-[Ru(azpy)(bpy)Cl(2)], 1 (alpha denoting the isomer in which the Cl ligands are cis related to each other and the pyridine ring of azpy is trans to the pyridine ring of bpy), are described. The solid-state structure of 1 has been determined by X-ray structure analysis. The IC(50) values obtained for several human tumor cell lines have indicated that compound 1 shows mostly a low to moderate cytotoxicity. The binding of the DNA model base 9-ethylguanine (9-EtGua) to the hydrolyzed species of 1 has been studied and compared to DNA model base binding studies of cis-[Ru(bpy)(2)Cl(2)] and alpha-[Ru(azpy)(2)Cl(2)]. The completely hydrolyzed species of 1, i.e., alpha-[Ru(azpy)(bpy)(H(2)O)(2)](2+), has been reacted with 9-EtGua in water at room temperature for 24 h. This resulted in the monofunctional binding of only one 9-EtGua, coordinated via the N7 atom. The product has been isolated as alpha-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2), 2, and characterized by 2D NOESY NMR spectroscopy. The NOE data show that the 9-EtGua coordinates (under these conditions) at the position trans to the azo nitrogen atom. Surprisingly, time-dependent (1)H NMR data of the 9-EtGua adduct 2 in acetone-d(6) show an unprecedented positional shift of the 9-EtGua from the position trans to the azo nitrogen to the position trans to the bpy nitrogen atom, resulting in the adduct alpha'-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2) (alpha' indicating 9-EtGua is trans to the bpy nitrogen). This positional isomerization of 9-EtGua is correlated to the cytotoxicity of 1 in comparison to both the cytotoxicity and 9-EtGua coordination of cis-[Ru(bpy)(2)Cl(2)], alpha-[Ru(azpy)(2)Cl(2)], and beta-[Ru(azpy)(2)Cl(2)]. This positional isomerization process is unprecedented in model base metal chemistry and could be of considerable biological significance.     

Structural, electronic, and acid/base properties of [Ru(bpy)2(bpy(OH)2)]2+ (bpy = 2,2'-bipyridine, bpy(OH)2 = 4,4'-dihydroxy-2,2'-bipyridine)

We have synthesized the complex [Ru(bpy)(2)(bpy(OH)(2))](2+) (bpy =2,2'-bipyridine, bpy(OH)(2) = 4,4'-dihydroxy-2,2'-bipyridine). Experimental results coupled with computational studies were utilized to investigate the structural and electronic properties of the complex, with particular attention paid toward the effects of deprotonation on these properties. The most distinguishing feature observed in the X-ray structural data is a shortening of the CO bond lengths in the modified ligand upon deprotonation. Similar results are also observed in the computational studies as the CO bond becomes double bond in character after deprotonating the complex. Electrochemically, the hydroxy-modified bipyridyl ligand plays a significant role in the redox properties of the complex. When protonated, the bpy(OH)(2) ligand undergoes irreversible reduction processes; however, when deprotonated, reduction of the substituted ligand is no longer observed, and several new irreversible oxidation processes associated with the modified ligand arise. pH studies indicate [Ru(bpy)(2)(bpy(OH)(2))](2+) has two distinct deprotonations at pK(a1) = 2.7 and pK(a2) = 5.8. The protonated [Ru(bpy)(2)(bpy(OH)(2))](2+) complex has a characteristic UV/Visible absorption spectrum similar to the well-studied complex [Ru(bpy)(3)](2+) with bands arising from Metal-to-Ligand Charge Transfer (MLCT) transitions. When the complex is deprotonated, the absorption spectrum is altered significantly and becomes heavily solvent dependent. Computational methods indicate that the deprotonated bpy(O(-))(2) ligand mixes heavily with the metal d orbitals leading to a new absorption manifold. The transitions in the complex have been assigned as mixed Metal-Ligand to Ligand Charge Transfer (MLLCT).     

Diastereoselective Synthesis, Spectroscopy, and Electrochemistry of Ruthenium(II) Complexes of Substituted Pyrazolylpyridine Ligands

We report the synthesis of the hetero- and homoleptic ruthenium(II) complexes Ru(bpy)(2)L(2+), Ru(bpy)L(2)(2+) (bpy is 2,2'-bipyridine), and RuL(3)(2+) of six new bidentates L, the substituted pyrazolylpyridines 1-6 (1-substituted-3-(2-pyridinyl)-4,5,6,7-tetrahydroindazoles with substituents R = H, CH(3), Ph, or C(6)H(4)-4"-COOX where X = H, CH(3), or C(2)H(5)). These were fully characterized by (1)H- and (13)C-NMR spectroscopy and elemental analysis. The UV-visible spectra and redox properties of the complexes, some in the ruthenium(III) and reduced bipyridine oxidation states, are also discussed. The substituents R played a role in determining the stereochemistry of the Ru(bpy)L(2)(2+) and RuL(3)(2+) products. The reaction of Ru(DMSO)(4)Cl(2) with 3 equiv of L bearing aromatic substituents gave only meridional RuL(3)(2+) isomers. The one-step reaction of Ru(bpy)Cl(3).H(2)O with 2 equiv of L provided a mixture of the three possible Ru(bpy)L(2)(2+) isomers, from which one symmetric isomer (labeled beta) was isolated pure. A trans arrangement of the pyrazole groups was deduced by (1)H-NMR and confirmed by X-ray crystallography for one such stereomer (beta-[Ru(bpy)(5)(2)](PF(6))(2), R = C(6)H(4)-4"-COOC(2)H(5)). In contrast, Ru(DMSO)(4)Cl(2) reacted with 2 equiv of L and then 1 equiv of bpy to selectively form the other symmetric isomer (labeled alpha) where the pyridine groups of L are trans. Crystal data for beta-[Ru(bpy)(5)(2)](PF(6))(2) (C(52)H(50)N(8)O(4)F(12)P(2)Ru) with Mo Kalpha (lambda = 0.710 73 ?) radiation at 295 K: a = 28.442(13) ?, b = 18.469(15) ?, c = 23.785(9) ?, beta = 116.76(0) degrees, monoclinic, space group C2/c, Z = 8. Fully anisotropic (except for H and disordered F atoms), full-matrix, weighted least-squares refinement on F(2) gave a weighted R on F(2) of 0.2573 corresponding to R on F of 0.1031 for data where F > 4sigma(F ).     

Octahedral Fe(II) and Ru(II) complexes based on a new bis 1,10-phenanthroline ligand that imposes a well defined axis.

A bis-chelating ligand (L1), made of two 7-(p-anisyl)-1,10-phenanthroline (phen) subunits connected with a p-(CH(2))(2)C(6)H(4)(CH(2))(2) spacer through their 4 positions, has been prepared, using Skraup syntheses and reaction of the anion of 4-methyl-7-anisyl-1,10-phenanthroline with alpha,alpha'-dibromo-p-xylene. Its Fe(II) complex, [FeL1(dmbp)](PF(6))(2), was prepared in one step by reaction of L1 with [Fe(dmbp)(3)](PF(6))(2) (dmbp = 4,4'-dimethyl-2,2'-bipyridine). On the other hand, its Ru(II) complex, [RuL1(dmbp)](PF(6))(2), was prepared in two steps from Ru(CH(3)CN)(4)Cl(2) and L1, followed by reaction with dmbp. X-ray crystal structure analyses show that in the two octahedral complexes, ligand L1 coils around the metal by coordination of the axial and two equatorial positions. It defines a 21 A long axis (O.O distance) running through the central metal and the terminal anisyl substituents. The complexes were also characterized by (1)H NMR, mass spectrometry, cyclic voltammetry, electronic absorption, and, in the case of Ru(II), fluorescence spectroscopy.     

Investigation of the electronic, photosubstitution, redox, and surface properties of new ruthenium(II)-containing amphiphiles

A series of pyridine- and phenol-based ruthenium(II)-containing amphiphiles with bidentate ligands of the following types are reported: [(L(PyI))Ru(II)(bpy)(2)](PF(6))(2) (1), [(L(PyA))Ru(II)(bpy)(2)](PF(6))(2) (2), [(L(PhBuI))Ru(II)(bpy)(2)](PF(6)) (3), and [(L(PhClI))Ru(II)(bpy)(2)](PF(6)) (4). Species 1 and 2 are obtained by treatment of [Ru(bpy)(2)Cl(2)] with the ligands L(PyI) (N-(pyridine-2-ylmethylene)octadecan-1-amine) and L(PyA) (N-(pyridine-2-ylmethyl)octadecan-1-amine). The imine species 3 and 4 are synthesized by reaction of [Ru(bpy)(2)(CF(3)SO(3))(2)] with the amine ligands HL(PhBuA) (2,4-di-tert-butyl-6-((octadecylamino)methyl)phenol), and HL(PhClA) (2,4-dichloro-6-((octadecylamino)methyl)phenol). Compounds 1-4 are characterized by means of electrospray ionization (ESI(+)) mass spectrometry, elemental analyses, as well as electrochemical methods, infrared and UV-visible absorption and emission spectroscopies. The cyclic voltammograms (CVs) of 1-2 are marked by two successive processes around -1.78 and -2.27 V versus Fc(+)/Fc attributed to bipyridine reduction. A further ligand-centered reductive process is seen for 1. The Ru(II)/Ru(III) couple appears at 0.93 V versus Fc(+)/Fc. The phenolato-containing 3 and 4 species present relatively lower reduction potentials and more reversible redox behavior, along with Ru(II/III) and phenolate/phenoxyl oxidations. The interpretation of observed redox behavior is supported by density functional theory (DFT) calculations. Complexes 1-4 are surface-active as characterized by compression isotherms and Brewster angle microscopy. Species 1 and 2 show collapse pressures of about 29-32 mN·m(-1), and are strong candidates for the formation of redox-responsive monolayer films.     

Ruthenium(II) complexes containing 8-(dimethylphosphino)quinoline (Me(2)Pqn): preparation,crystal structures,and electrochemical and spectroscopic properties of [Ru(bpy or phen)(3)(-)(n)(Me(2)Pqn)(n)](PF(6))(2) (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; n = 1, 2, or 3)

Several new ruthenium(II) complexes containing 8-(dimethylphosphino)quinoline (Me(2)Pqn) were synthesized, and their structures and electrochemical/spectroscopic properties have been investigated. In addition to the mono(Me(2)Pqn) complex [Ru(bpy or phen)(2)(Me(2)Pqn)](PF(6))(2) (1 or 1'; bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline), the geometrical isomers trans(P)- and C(1)-[Ru(bpy)(Me(2)Pqn)(2)](PF(6))(2) (tP-2 and C(1)-2) and mer- and fac-[Ru(Me(2)Pqn)(3)](PF(6))(2) (m-3 and f-3) were also selectively synthesized and isolated. It was found that complexes tP-2 and m-3 were converted quantitatively to the corresponding C(1)-2 and f-3 isomers, respectively, by irradiation of light corresponding to the MLCT transition energy. The strong trans influence of the Me(2)P- donor group of Me(2)Pqn was confirmed by the X-ray structural analyses for 1, tP-2, m-3, and f-3. Cyclic voltammetry of a series of complexes, [Ru(bpy)(3)](PF(6))(2), 1, C(1)-2, and f-3, exhibited a reversible one-electron oxidation wave and two or three one-electron reduction waves. The oxidation potentials of the complexes gave a large positive shift with increasing number of coordinated Me(2)Pqn molecules, indicating a larger pi-acceptability of the Me(2)P- group compared with bpy or qn. Complex f-3 in EtOH/MeOH (4:1) glass at 77 K exhibited an intense long-lived (tau = 920 microseconds) emission arising from the quinoline-based (3)(pi-pi) excited state. In contrast, the mixed-ligand complexes 1, 1', and C(1)-2 showed a characteristic dual emission, giving a double-exponential emission decay, and the dual emission originates from both the bpy-based (3)MLCT and the quinoline-based (3)(pi-pi) emitting states.     

New dicarboxylic acid bipyridine ligand for ruthenium polypyridyl sensitization of TiO2

An ambidentate dicarboxylic acid bipyridine ligand, (4,5-diazafluoren-9-ylidene) malonic acid (dfm), was synthesized for coordination to Ru(II) and mesoporous nanocrystalline (anatase) TiO(2) thin films. The dfm ligand provides a conjugated pathway from the pyridyl rings to the carbonyl carbons of the carboxylic acid groups. X-ray crystal structures of [Ru(bpy)(2)(dfm)]Cl(2) and the corresponding diethyl ester compound, [Ru(bpy)(2)(defm)](PF(6))(2), were obtained. The compounds displayed intense metal-to-ligand charge transfer (MLCT) absorption bands in the visible region (ε > 11,000 M(-1) cm(-1) for [Ru(bpy)(2)(dfm)](PF(6))(2) in acetonitrile). Significant room temperature photoluminescence, PL, was absent in CH(3)CN but was observed at 77 K in a 4:1 EtOH:MeOH (v:v) glass. Cyclic voltammetry measurements revealed quasi-reversible Ru(III/II) electrochemistry. Ligand reductions were quasi-reversible for the diethyl ester compound [Ru(bpy)(2)(defm)](2+), but were irreversible for [Ru(bpy)(2)(dfm)](2+). Both compounds were anchored to TiO(2) thin films by overnight reactions in CH(3)CN to yield saturation surface coverages of 3 × 10(-8) mol/cm(2). Attenuated total reflection infrared measurements revealed that the [Ru(bpy)(2)(dfm)](2+) compound was present in the deprotonated carboxylate form when anchored to the TiO(2) surface. The MLCT excited states of both compounds injected electrons into TiO(2) with quantum yields of 0.70 in 0.1 M LiClO(4) CH(3)CN. Micro- to milli-second charge recombination yielded ground state products. In regenerative solar cells with 0.5 M LiI/0.05 M I(2) in CH(3)CN, the Ru(bpy)(2)(dfm)/TiO(2) displayed incident photon-to-current efficiencies of 0.7 at the absorption maximum. Under the same conditions, the diethylester compound was found to rapidly desorb from the TiO(2) surface.