Ruthenium(II/III) mediated transformation of 1,2-bis(2′-pyridylmethyleneimino)benzene (L) to 2-(2′-benzimidazolyl)pyridine (L′H) and its in situ formed complexes with Ru(II): X-ray structure of trans-[Ru(PPh3)2(L′H)2](ClO4)2

A series of ruthenium (II) complexes of formulae trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ (1), [Ru(bpy)(L′H)₂](ClO₄)₂ (2), [Ru(bpy)₂(L′H)](ClO₄)₂ (3), cis-[Ru(DMSO)₂(L′H)₂]Cl₂ (4), and [Ru(L′H)₃](PF₆)₂ (5) (where L′H = 2-(2′-benzimidazolyl)pyridine) have been synthesized by reaction of the appropriate ruthenium precursor with 1,2-bis(2′-pyridylmethyleneimino)benzene (L). The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. All the complexes were found to be diamagnetic and hence metal is in +2 oxidation state. The molecular structure of trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ has been determined by the single crystal X-ray diffraction studies. The molecular structure shows that Ru(II) is at the center of inversion of an octahedron with N₄P₂ coordination sphere. The ligand acts as a bidentate N,N′donor. The electronic spectra of the complexes display intense MLCT bands in the visible region.Cyclic voltammetric studies show quasi-reversible oxidative response at 0.99-1.32 V (vs Ag/AgCl reference electrode) due to Ru(III)/Ru(II) couple.     

Supramolecular assemblies of new 2-D complexes: Syntheses, crystal structures, spectroscopic and magnetic properties of {[MnAu2(CN)4(NITpPy)2(H2O)2]}n and {[Co(N(CN)2)2(NITpPy)2(H2O)2]}n

Two new complexes, {[MnAu₂(CN)₄(NITpPy)₂(H₂O)₂]}_n (1) and {[Co(N(CN)₂)₂(NITpPy)₂(H₂O)₂]}_n (2), have been synthesized and characterized. The single-crystal X-ray analysis for the complexes 1 and 2 demonstrates that each M(II) (M = Mn or Co) ion assumes a distorted octahedral MN₄O₂ coordination polyhedron. Four nitrogen atoms come from the cyanide groups and the pyridyl rings in a common plane, and two oxygen atoms come from the H₂O molecules in trans-positions. The structures of complexes 1 and 2 illustrate that aurophilicity and/or hydrogen bonding interactions play important roles in increasing dimensionality. Magnetic investigations on complexes 1 and 2 show the presence of weak antiferromagnetic interactions.     

Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Versatile coordination behaviour of Ph2AsCH2AsPh2 with Ru(II)

Treatment of ‘RuCl₃ · 3H₂O’ with Ph₂AsCH₂AsPh₂ (dpam) in hot EtOH gives either trans-[RuCl₂(dpam-As,As′)(dpam-As)₂] (1), or cis-[RuCl₂(dpam-As,As′)₂] (2), depending on the mole ratio. On exposure to light, solutions of 2 isomerise to trans-[RuCl₂(dpam-As,As′)₂] (3). Treatment of [RuCl₂(PPh₃)₃] with two equivalents of dpam in CH₂Cl₂ gave a mixture of two products, from which trans-[RuCl₂(PPh₃) (dpam-As,As′)(dpam-As)] (4) was isolated by recrystallisation. The crystal structures of 1-4 are reported. Complexes 1-3 in CH₂Cl₂ undergo electrochemical oxidation to Ru(III), and the Ru(III) form of 2 undergoes isomerisation on the voltammetric timescale to the Ru(III) form of 3.     

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)] and [Ru(bpy)2(nitatp)]

Two new ruthenium complexes [Ru(bpy)₂(mitatp)](ClO₄)₂1 and [Ru(bpy)₂(nitatp)](ClO₄)₂2 (bpy = 2,2′-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (¹O₂) was proved to contribute to the DNA photocleavage process, the ¹O₂ quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process.     

Synthetic and mechanistic studies on ruthenium dicarbonyl complexes containing PhP(CH2CH2CH2PCy2)2 (Cyttp) ligand

A synthetic and mechanistic study is reported on ligand substitution and other reactions of six-coordinate ruthenium(II) carbonyl complexes containing tridentate PhP(CH₂CH₂CH₂PCy₂)₂ (Cyttp). Carbonylation of cis-mer-Ru(OSO₂CF₃)₂(CO)(Cyttp) (1) affords [cis-mer-Ru(OSO₂CF₃)(CO)₂(Cyttp)]O₃SCF₃ (2(O₃SCF₃)) and, on longer reaction times, [cis-mer-Ru(solvent)(CO)₂(Cyttp)](O₃SCF₃)₂ (solvent = acetone, THF, methanol). 2(O₃SCF₃) reacts with each of NaF, LiCl, LiBr, NaI, and LiHBEt₃ to yield [cis-mer-RuX(CO)₂(Cyttp)]⁺ (X = F (3), Cl (4), Br (5), I (6), H (7)), isolated as 3-7(BPh₄). These conversions proceed with high stereospecificity to afford only a single isomer of the product that is assigned a structure in which the Ph group of Cyttp points toward the CO trans to X (anti when X = F, Cl, Br, or I; syn when X = H). Treatment of 2(O₃SCF₃) with NaOMe and CO generates the methoxycarbonyl complex [cis-mer-Ru(CO₂Me)(CO)₂(Cyttp)]⁺ (8), whereas addition of excess n-BuLi to 2(O₃SCF₃) in THF under CO affords mer-Ru(CO)₂(Cyttp) (9). The two ¹³C isotopomers [cis-mer-Ru(OSO₂CF₃)(CO)(¹³CO)(Cyttp)]O₃SCF₃ (2′(O₃SCF₃): ¹³CO trans to P_C; 2″(O₃SCF₃): ¹³CO cis to all P donors) were synthesized by appropriate adaptations of known transformations and used in mechanistic studies of reactions with each of LiHBEt₃, NaOMe/CO, and n-BuLi. Whereas LiHBEt₃ reacts with 2′(O₃SCF₃) and 2″(O₃SCF₃) to replace triflate by hydride without any scrambling of the carbonyl ligands, the corresponding reactions of NaOMe-CO are more complex. The methoxide combines with the CO cis to triflate in 2, and the resultant methoxycarbonyl ligand ends up positioned trans to the incoming CO in 8. A mechanism is proposed for this transformation. Finally, treatment of either 2′(O₃SCF₃) or 2″(O₃SCF₃) with an excess of n-BuLi leads to the formation of the same two ruthenium(0) isomers of mer-Ru(CO)(¹³CO)(Cyttp). These products represent, to our knowledge, the first example of a syn-anti pair of isomers of a five-coordinate metal complex.     

Ligand effects in cis-Ru(N-N)2L2 species where N-N is a substituted 2,2′-bisoxazoline and L is monodentate

Starting from previously reported cis-Ru(MeL)₂Cl₂, where MeL is 4,4,4′,4′-tetramethyl-2,2′-bisoxazoline, cis-Ru(MeL)₂Br₂ (1), cis-Ru(MeL)₂I₂ (2), cis-Ru(MeL)₂(NCS)₂ · H₂O (3), cis-Ru(MeL)₂(N₃)₂ (4) and cis-[Ru(MeL)₂(MeCN)₂](PF₆)₂ · (CH₃)₂CO (5) are synthesised. The X-ray crystal structures of complexes 1, 2, 3 and 5 have been determined. All the five new complexes have been characterized by FTIR, ESIMS and ¹H NMR. In cyclic voltammetry in acetonitrile at a glassy carbon electrode, the complexes display a quasireversible Ru(II/III) couple in the range 0.32-1.71 V versus NHE. The Ru(II/III) potentials yield a satisfactorily linear correlation with Chatt’s ligand constants P_L for the monodantate ligands. From the intercept and by comparing the known situation in Ru(2,2′-bipyridine)₂L₂, it is concluded that MeL, a non-aromatic diimine, is significantly more π-acidic than 2,2′-bipyridine.     

Sn-S and Ru-Ru bonds cleavage reactions between [Ph3SnS(CH2)3SSnPh3] and Ru3(CO)12: X-ray crystal structures of [Ph3SnS(CH2)3SSnPh3] and trans-[Ru(CO)4(SnPh3)2]

The organotin complex [Ph₃SnS(CH₂)₃SSnPh₃] (1) was synthesized by PdCl₂ catalyzed reaction between Ph₃SnCl and disodium-1,3-propanedithiolate which in turn was prepared from 1,2-propanedithiol and sodium in refluxing THF. Reaction of 1 with Ru₃(CO)₁₂ in refluxing THF affords the mononuclear complex trans-[Ru(CO)₄(SnPh₃)₂] (2) and the dinuclear complex [Ru₂(CO)₆(μ-κ²-SCH₂CH₂CH₂S)] (3) in 20 and 11% yields, respectively, formed by cleavage of Sn-S bond of the ligand and Ru-Ru bonds of the cluster. Treatment of pymSSnPPh₃ (pymS = pyrimidine-2-thiolate) with Ru₃(CO)₁₂ at 55-60 °C also gives 2 in 38% yield. Both 1 and 2 have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction analysis.     

A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine-phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1-4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)₂I₂(P∩S)] (1a) {P∩S = η²-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)₂I₂(P∼S)] (1b-d) {P∼S = η¹-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)₂I₂]_n with equimolar quantity of the ligands Ph₂P(CH₂)_nP(S)Ph₂ {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)₂I₂(P∼S)₂] (2a-d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028-2103 cm⁻¹. The ν(PS) band of complex 1a occurs 23 cm⁻¹ lower region compared to the corresponding free ligand suggesting chelation via metal-sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopy.     

Synthesis and characterisation of bis(2,2′-bipyridine)(4-carboxy-4′-(pyrid-2-ylmethylamido)-2,2′-bipyridine)ruthenium(II) di(hexafluorophosphate): Comparison of spectroelectrochemical properties with related complexes

The new complex, [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂ NHCO-bpy)](PF₆)₂ · 3H₂O (1), where 4-HCOO-4′-pyCH₂NHCO-bpy is 4-(carboxylic acid)-4′-pyrid-2-ylmethylamido-2,2′-bipyridine, has been synthesised from [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ (H₂dcbpy is 4,4′-(dicarboxylic acid)-2,2′-bipyridine) and characterised by elemental analysis and spectroscopic methods. An X-ray crystal structure determination of the trihydrate of the [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ precursor is reported, since it represented a different solvate to an existing structure. The structure shows a distorted octahedral arrangement of the ligands around the ruthenium(II) centre and is consistent with the carboxyl groups being protonated. A comparative study of the electrochemical and photophysical properties of [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂NHCO-bpy)]²⁺ (1), [Ru(bpy)₂(H₂dcbpy)]²⁺ (2), [Ru(bpy)₃]²⁺ (3), [Ru(bpy)₂Cl₂] (4) and [Ru(bpy)₂Cl₂]⁺ (5) was then undertaken to determine their variation upon changing the ligands occupying two of the six ruthenium(II) coordination sites. The ruthenium(II) complexes exhibit intense ligand centred (LC) transition bands in the UV region, and broad MLCT bands in the visible region. The ruthenium(III) complex, 5, displayed overlapping LC bands in the UV region and a LMCT band in the visible. 1, 2 and 3 were found, via cyclic voltammetry at a glassy carbon electrode, to exhibit very positive reversible formal potentials of 996, 992 and 893 mV (versus Fc/Fc⁺) respectively for the Ru(III)/Ru(II) half-cell reaction. As expected the reversible potential derived from oxidation of 4 (−77 mV (versus Fc/Fc⁺)) was in excellent agreement with that found via reduction of 5 (−84 mV (versus Fc/Fc⁺)). Spectroelectrochemical experiments in an optically transparent thin-layer electrochemical cell configuration allowed UV-Vis spectra of the Ru(III) redox state to be obtained for 1, 2, 3 and 4 and also confirmed that 5 was the product of oxidative bulk electrolysis of 4. These spectrochemical measurements also confirmed that the oxidation of all Ru(II) complexes and reduction of the corresponding Ru(III) complex are fully reversible in both the chemical and electrochemical senses.     

Conductometric and voltammetric studies on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2], where L: 2-(2′-pyridyl)quinoxaline

Conductometric investigation on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl₂(L)(PPh₃)₂] (A) (where PPh₃: triphenyl phosphine and L: 2-(2′-pyridyl)quinoxaline, C₁₃N₃H₉), in dimethylsulfoxide (DMSO) was performed at temperatures ranging from 25 to 50 °C. In addition, cyclic voltammograms of A were recorded on platinum working electrode in dichloromethane (DCM) and dimethylsulfoxide (DMSO) using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte at 25 °C. The molar conductivities (Λ) demonstrate that A behaves as uni-univalent electrolyte in DMSO over the whole temperature range. This behavior can be explained in terms of the replacement upon dissolution of chlorine and PPh₃ ligands by DMSO molecules, and consequently, the formation of the ion-pair [RuCl(L)(PPh₃)(DMSO)₂]Cl [B⁺Cl⁻] which is dissociated in some extent. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ^o) and the ion-pair association constants (K_A) of [B⁺Cl⁻]. The limiting ion conductivities for the B⁺ ion were evaluated using n-tetrabutylammonium chloride (NBu₄Cl) as “reference electrolyte”. The thermodynamic functions related with the ion association, such as Gibbs free energy , enthalpy , and entropy , were evaluated as well. The mobility of B⁺ was found to increase linearly with rising temperature and the consequent decrease of the viscosity (η) of DMSO. The K_A and values indicate that the association of [B⁺Cl⁻] increases to some extent with the rise of the temperature followed by the decrease of the dielectric constant (ε) of DMSO. The voltammetric experiments indicated that the couple Ru^3+/2+ is reversible and diffusion controlled in DCM and completely irreversible in DMSO.     

Synthesis and structural characterization of a novel diosmium(III) compound: Os2(ap)4Cl2

The reaction between Os₂(OAc)₄Cl₂ and Hap (Hap is 2-anilinopyridine) under prolonged refluxing conditions resulted in a new Os₂(III) compound, Os₂(ap)₄Cl₂ (1). The molecular structure of 1 was determined from a single crystal X-ray diffraction study, which revealed an Os-Os bond length of 2.396[1] Å, and a cis-(2,2) arrangement of the ap ligands. Also reported are magnetic, electrochemical and spectroscopic properties of 1.     

Synthesis, structure and reactivity of complexes containing [M(S2)2] fragments (M=Ru, Os; (S2)=1,2-benzenedithiolate (2−))

Subsequent addition of 1,2-benzenedithiol (S₂-H₂) and nBuLi to a solution of [Ru(NO)Cl₃ · xMeOH] in THF afforded exclusively the monomeric species NBu₄[Ru^II(NO)(S₂)₂] (1). Formation of dimeric (NBu₄)₂[Ru^II(NO)(S₂)₂]₂ (2) has been confirmed when the deprotonated ligand S₂-Li₂ was added to [Ru(NO)Cl₃ · xMeOH] and allowed to stir for 30 h. The monomer 1 undergoes aerial oxidation to give (NBu₄)₂[Ru^IV(S₂)₃] (3). The reaction between RuCl₃ · xH₂O and S₂-H₂ in the presence of NaOMe, afforded the dinulear Ru^III species (NMe₄)₂[Ru^III(S₂)₂]₂ (4). A modified method for the preparation of 1 is being employed to synthesize the osmium analogue NBu₄[Os(NO)(S₂)₂] (5) effectively. The solid state structures of 1, 2 and 3 were determined by X-ray crystal structure analysis. A comparison of relevant bond distance data suggests that 1,2-benzenedithiolate acts as an “innocent” ligand.     

Cyclometalated ruthenium(II) complexes of benzo[h]quinoline (bzqH)[Ru(bzq)(NCMe)4], [Ru(bzq)(LL)(NCMe)2], and [Ru(bzq)(LL)2] (LL = bpy, phen)

Cyclometalation of benzo[h]quinoline (bzqH) by [RuCl(μ-Cl)(η⁶-C₆H₆)]₂ in acetonitrile occurs in a similar way to that of 2-phenylpyridine (phpyH) to afford [Ru(bzq)(MeCN)₄]PF₆ (3) in 52% yield. The properties of 3 containing ‘non-flexible’ benzo[h]quinoline were compared with the corresponding [Ru(phpy)(MeCN)₄]PF₆ (1) complex with ‘flexible’ 2-phenylpyridine. The [Ru(phpy)(MeCN)₄]PF₆ complex is known to react in MeCN solvent with ‘non-flexible’ diimine 1,10-phenanthroline to form [Ru(phpy)(phen)(MeCN)₂]PF₆, being unreactive toward ‘flexible’ 2,2′-bipyridine under the same conditions. In contrast, complex 3 reacts both with phen and bpy in MeCN to form [Ru(bzq)(LL)(MeCN)₂]PF₆ {LL = bpy (4) and phen (5)}. Similar reaction of 3 in methanol results in the substitution of all four MeCN ligands to form [Ru(bzq)(LL)₂]PF₆ {LL = bpy (6) and phen (7)}. Photosolvolysis of 4 and 5 in MeOH occurs similarly to afford [Ru(bzq)(LL)(MeCN)(MeOH)]PF₆ as a major product. This contrasts with the behavior of [Ru(phpy)(LL)(MeCN)₂]PF₆, which lose one and two MeCN ligands for LL = bpy and phen, respectively. The results reported demonstrate a profound sensitivity of properties of octahedral compounds to the flexibility of cyclometalated ligand. Analogous to the 2-phenylpyridine counterparts, compounds 4-7 are involved in the electron exchange with reduced active site of glucose oxidase from Aspergillus niger. Structure of complexes 4 and 6 was confirmed by X-ray crystallography.     

A rare example of a di-cationic hydrido carbonyl tetra-nuclear cluster, [H2Rh2Pt2(CO)7(PPh3)3]

Addition of excess CF₃CO₂H (HTFA) to [Rh₂Pt₂(CO)₇(PPh₃)₃], I, under nitrogen results in the formation of a salt (X²⁺ Y²⁻), which contains only the second example of a di-cationic carbonyl hydride tetra-nuclear cluster, [H₂Rh₂Pt₂(CO)₇(PPh₃)₃]²⁺, X²⁺, and a presently partially characterized polymetallic anion Y²⁻. The di-cation X²⁺ has been characterized by mass spectrometry and a variety of multinuclear NMR methods. Since there is no difference in the electron count for I and X²⁺, it is probable that both I and X²⁺ adopt similar butterfly metallic frameworks with a Rh-Rh hinge; in X²⁺, there are two bridging hydrides to the same wing-tip Pt but the phosphine site occupancies on the Rh₂Pt₂-framework in I and X²⁺ are different.     

Synthesis, characterization and 1D helical chain crystal structure of [Cu(DBA)2(1,10-phen)]n and [Cd(DBA)2(1,10-phen)2] (DBA = benzilic acid)

Two novel complexes [Cu(DBA)₂(1,10-phen)]_n (1) and [Cd(DBA)₂(1,10-phen)₂] (2) [HDBA = benzilic acid: (C₆H₅)₂C(OH)COOH] have been synthesized and characterized by element analysis and fluorescence spectroscopy. The crystal structures of compounds 1, 2 and HDBA (3) were also determined. Complex 1 is a one-dimensional (1D) helical infinite chain, in which [(1,10)-phen]Cu^(II) units were bridged by benzilic acid. Complex 2 is a mononuclear structure, and is self-assembled through π-π stacking interactions to form a 1D helical chain. Compound 3 is self-assembled to form a 1D helical chain through hydrogen bonds interactions. Thermal analyses indicate that complexes 1 and 2 are stable under 200 and 254 °C in solid state, respectively.     

Synthesis, structure and properties of TTF-carboxylate bridged paddlewheel dirhodium complexes, Rh2(BuCO2)3(TTFCO2) and Rh2(BuCO2)2(TTFCO2)2

Reaction of tetrathiafulvalene carboxylic acid (TTFCO₂H) with paddlewheel dirhodium complex Rh₂(Bu^tCO₂)₄ yielded TTFCO₂-bridged complexes Rh₂(Bu^tCO₂)₃(TTFCO₂) (1) and cis- and trans-Rh₂(Bu^tCO₂)₂(TTFCO₂)₂ (cis- and trans-2). Their triethylamine adducts [1(NEt₃)₂] and cis-[2(NEt₃)₂] were purified and isolated with chromatographic separation, and characterized with single crystal X-ray analysis. Trans-[2(NEt₃)₂] is not completely separated from a mixture of cis- and trans-[2(NEt₃)₂], but its single crystals were obtained from a solution of the mixture. A three-step quasi-reversible oxidation process was observed for 1 in MeCN. The first two steps correspond to the oxidation of the TTFCO₂ moiety and the last one is the oxidation of the Rh₂ core. The oxidation of cis-2 is observed as a two-step process with very similar E_1/2 values to those of the first two processes for 1. Both 1⁺ and cis-2²⁺ in MeCN at room temperature show isotropic ESR spectra with a g value of 2.008 and a_H = 0.135 mT for two equivalent H atoms and a_H = 0.068 mT for one H atom. The redox and ESR data of cis-2 suggest that the intramolecular interaction between the TTF moieties is very small.     

Hydrogen bonding: further evidence for the cause of the color change of nitrosylpentaamminechromium (III) compounds. Crystal structures of [Cr(NO)(NH3)5](PF6)2 and [Cr(NO)(NH3)5]Cl(PF6)

The crystal structures of [Cr(NO)(NH₃)₅](PF₆)₂ (red) and [Cr(NO)(NH₃)₅]Cl(PF₆) (brown) have been determined. The [Cr(NO)(NH₃)₅]²⁺(A) complex cations in these compounds have a slightly distorted octahedral geometry with a strictly linear Cr-N-O arrangement (from symmetry). The short interatomic distances (2.399 Å × 4) between the O (nitrosyl) and H (ammonia in adjacent complex cations) atoms in A(PF₆)₂ indicate the existence of hydrogen bonds, while the interatomic distances (3.258 Å × 8) between those in ACl(PF₆) are much longer, and the hydrogen bonds should be weak in spite of the presence of the smaller counter anion of chloride ion in ACl(PF₆). Comparisons of the five crystal structures of A(PF₆)₂, ACl₂, ACl(ClO₄), ACl(PF₆), and A(ClO₄)₂ have led to the conclusion that the existence of the strong hydrogen bonds gives red crystals of A(PF₆)₂, while the absence of hydrogen bonds results in the formation of green crystals of A(ClO₄)₂ (O ? H, 3.595 Å × 2). The color change of the crystals (from red to green) with the change of outer sphere anions is attributed to the change of the strength of the hydrogen bonding between the complex cations.     

Unexpected formation and structure elucidation of mer-[RuCl3(TMSO)(bpy)] derived from [H(TMSO)][trans-RuCl4(TMSO)2] under mild condition

Treatment of [H(TMSO)][trans-RuCl₄(TMSO)₂] (1) with 2,2′-bipyridine (bpy) in ethanol at room temperature resulted an unknown mer-[RuCl₃(TMSO)(bpy)] (3) and a known cis-[RuCl₂(TMSO)₄] (4) (TMSO =  tetramethylene sulfoxide) complexes. The 3 was obtained by the substitution with bpy in mer-[RuCl₃(TMSO)₃] (2), whereas 4 was obtained by one-electron reduction of 2, suggesting that 2 is a precursor for both 3 and 4. The structure of 3 was determined by single crystal X-ray diffraction. The reaction is a new synthetic procedure for 3 and/or 3 and 4 in mild reaction conditions from the anionic complex 1. It involves simultaneous substitution and redox reaction. This is the first known example of precisely characterized Ru(III)-chloride-TMSO-bpy-complex derived from anionic [H(TMSO)][trans-RuCl₄(TMSO)₂] at room temperature.     

Reactivity of the N-heterocyclic carbene complexes [Ru(IMes)2(CO)HX] (X = OH, Cl) with alkynes

Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)₂(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)₂(CO)H(CCR)] (R = Ph 3, SiMe₃, 4) and [Ru(IMes)₂(CO)(CCR)₂] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru-OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru-H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)₂(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru-H bond to yield the alkenyl chloride complex [Ru(IMes)₂(CO)(CHCHPh)Cl] 8. Complexes 3-8 have been structurally characterised by X-ray crystallography.