Light-induced metastable linkage isomers of ruthenium sulfur dioxide complexes

The irradiation of ruthenium-sulfur dioxide complexes of general formula trans-[Ru(II)(NH(3))(4)(SO(2))X]Y with laser light at low temperature results in linkage isomerization of SO(2), starting with eta(1)-planar S-bound to eta(2)-side S,O-bound SO(2). The solid-state photoreaction proceeds with retention of sample crystallinity. Following work on trans-[Ru(NH(3))(4)Cl(eta(1)-SO(2))]Cl and trans-[Ru(NH(3))(4)(H(2)O)(eta(1)-SO2)](C(6)H(5)SO(3))(2) (Kovalevsky, A. Y.; Bagley, K. A.; Coppens, P. J. Am. Chem. Soc. 2002, 124, 9241-9248), we describe photocrystallographic, IR, DSC, and theoretical studies of trans-[Ru(II)(NH(3))(4)(SO(2))X]Y complexes with (X = Cl(-), H(2)O, or CF(3)COO(-) (TFA(-))) and a number of different counterions (Y = Cl(-), C(6)H(5)SO(3)(-), Tos(-), or TFA(-)). Low temperature IR experiments indicate the frequency of the asymmetric and symmetric stretching vibrations of the Ru-coordinated SO(2) to be downshifted by about 100 and 165 cm(-1), respectively. Variation of the trans-to-SO(2) ligand and the counterion increases the MS2 decay temperature from 230 K (trans-[Ru(II)(NH(3))(4)(SO(2))Cl]Cl) to 276 K (trans-[Ru(II)(NH(3))(4)(SO(2))(H(2)O)](Tos)(2)). The stability of the MS2 state correlates with increasing sigma-donating ability of the trans ligand and the size of the counterion. Quantum chemical DFT calculations indicate the existence of a third eta(1)-O-bound (MS1) isomer, the two metastable states being 0.1-0.6 eV above the energy of the ground-state complex.     

Photoconversion bonding mechanism in ruthenium sulfur dioxide linkage photoisomers revealed by in situ diffraction

Three new ruthenium-sulfur dioxide linkage photoisomeric complexes in the [Ru(NH(3))(4)(SO(2))X]Cl(2)·H(2)O family (X = pyridine (1); 3-chloropyridine (2); 4-chloropyridine (3)) have been developed in order to examine the effects of the trans-ligand on the nature of the photo-induced SO(2) coordination to the ruthenium ion. Solid-state metastable η(1)-O-bound (MS1) and η(2)-side S,O-bound (MS2) photoisomers are crystallographically resolved by probing a light-induced crystal with in situ diffraction. This so-called photocrystallography reveals the highest known photoconversion fraction of 58(3)% (in 1) for any solid-state SO(2) linkage photoisomer. The decay of this MS1 into the MS2 state was modeled via first-order kinetics with a non-zero asymptote. Furthermore, the MS2 decay kinetics of the three compounds were examined according to their systematically varying trans-ligand X; this offers the first experimental evidence that the MS2 state is primarily stabilized by donation from the S-O(bound) electrons into the Ru dσ-orbital rather than π-backbonding as previously envisaged. This has important consequences for the optoelectronic application of these materials since this establishes, for the first time, a design protocol that will enable one to control their photoconversion levels.     

Evidence of four light-induced metastable states in iron-nitrosyl complexes

Thermodynamic measurements on irradiated Na₂[Fe(CN)₅NO]⋅ 2H₂O reveal the existence of four light-induced long-lived metastable states, which decay exponentially in time. The activation energies and frequency factors of the four independent states are determined from isothermal calorimetric and differential scanning calorimetric measurements.     

Photocrystallographic identification of metastable nitrito linkage isomers in a series of nickel(II) complexes

Single crystal photocrystallographic experiments and solid state Raman spectroscopy have been used to determine the low temperature, metastable structures of the nickel(ii) nitrito complexes [Ni(aep)(2)(η(1)-ONO)(2)] 1#O (aep = 1-(2-aminoethyl)piperidine), [Ni(aem)(2)(η(1)-ONO)(2)] 2#O (aem = 1-(2-aminoethyl)morpholine), and [Ni(aepy)(2)(η(1)-ONO)(2)] 3#O (aepy = 1-(2-aminoethyl)pyrrolidine and where the #O denotes the oxygen-bound nitrito metastable molecule). These linkage isomers of the equivalent nitro complexes [Ni(aep)(2)(η(1)-NO(2))(2)] 1, [Ni(aem)(2)(η(1)-NO(2))(2)] 2 and [Ni(aepy)(2)(η(1)-NO(2))(2)] 3 are formed by LED irradiation at temperatures below 120 K. The behavior of the three complexes upon irradiation is generally similar, but some subtle differences have been observed. From the crystallographic studies all three complexes 1-3 exhibit the endo-nitrito linkage isomer upon irradiation, however, for 3# (a crystal structure that contains components of both 3 and 3#O) an exo-nitrito isomer is also observed. Under conditions of 90-100 K, with blue light, the conversion percentages to the nitrito isomers, 1#O, 2#O and 3#O were 16%, 22% and 30%, respectively. At temperatures below 110 K all three nitrito isomers were stable for over four hours but while 2#O and 3#O could be detected at temperatures down to 30 K, at temperatures below 60 K the metastable structure 1#O appeared to be quenched and only the nitro isomer 1 was identified in the crystal. The solid state Raman spectra for 1#, 2# and 3# confirmed the photocrystallographic results with the nitrito isomers being identified from the O-N-O deformation vibrations.     

Formation of linkage isomers via the substitution of halides by selenocyanate in ruthenium(III) complexes

Summary Substitution of the halide ion of [Ru(NH₃)₅X]²⁺ (X=Cl^– or Br^–) by SeCN^– was monitored spectrophotometrically between 45 and 60° C in aqueous medium. The pseudo-first order rate constants were evaluated by Guggenheim's procedure, which shows linearity for 2–3 half-lives. The rate increases linearly with [SeCN^–] and all the plots have a positive intercept on the rate axis. The SeCN^–-independent path represents aquation and the SeCN^–-dependent path represents anation of the aqua complex with simultaneous formation of two isomeric (the N bonded and the Se bonded) products. The formation of the isomeric products is entropy controlled.     

Electronic structure of metastable isomers of Ru nitroso complexes

Geometrical structures of nitroso complexes trans- [Ru(NO)(NH₃)₄(Cl)]²⁺, trans-[Ru(NO)(NH₃)₄(H2O)]³⁺, [Ru(NO)(Cyclam)(Cl)]²⁺(Cyclam is 1,4,8,11-tetraazocyclodecane), and [Ru(NO)(Bipy)₂(Cl)]²⁺ (Bipy is 2,2-bipyridine) are optimized using the density functional method. The potential energy surface of all four complexes was found to contain local minima corresponding to a stable state with the ¹-coordination of NO through the N atom and to two metastable isomers with the ¹-O and ²-NO coordination. For [Ru(NO)Cl₅)]^2-, trans-[Ru(NO)(NH₃)₄(Cl)]²⁺, and trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺, the lowest electronically excited triplet states are calculated, as well as the reduced complexes with one additional electron. It is shown that the electron excitation and reduction are accompanied by bending of the RuNO group with a substantial elongation of the Ru-O and N-O bonds, which makes this group unstable. These processes do not cause any significant changes in the metal or in the nitroso ligand oxidation states because of the electron density delocalization in the RuNO group.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 32–42.Original Russian Text Copyright © 2005 by Sizova, Lubimova.     

Accurate thermochemistry and spectroscopy of the oxygen-protonated sulfur dioxide isomers

Despite the promising relevance of protonated sulfur dioxide in astrophysical and atmospheric fields, its thermochemical and spectroscopic characterization is very limited. High-level quantum-chemical calculations have shown that the most stable isomer is the cis oxygen-protonated sulfur dioxide, HOSO(+), while the trans form is about 2 kcal mol(-1) less stable; even less stable (by about 42 kcal mol(-1)) is the S-protonated isomer [V. Lattanzi et al., J. Chem. Phys., 2010, 133, 194305]. The enthalpy of formation for the cis- and trans-HOSO(+) is presented, based on the well tested HEAT protocol [A. Tajti et al., J. Chem. Phys., 2004, 121, 11599]. Systematically extrapolated ab initio energies, accounting for electron correlation through coupled cluster theory, including up to single, double, triple and quadruple excitations, have been corrected for core-electron correlation, anharmonic zero-point vibrational energy, diagonal Born-Oppenheimer and scalar relativistic effects. As a byproduct, proton affinity of sulfur dioxide and atomization energies have also been obtained at the same levels of theory. Vibrational and rotational spectroscopic properties have been investigated by means of composite schemes that allow us to account for truncation of basis set as well as core correlation. Where available, for both thermochemistry and spectroscopy, very good agreement with experimental data has been observed.     

Carbon dioxide reduction by mononuclear ruthenium polypyridyl complexes

New mononuclear ruthenium complexes with general formula [Ru(bid)(B)(Cl)] (bid is (1Z,3Z)-1,3-bis(pyridin-2-ylmethylene)isoindolin-2-ide; B = bidentate ligand 2,2'-bipyridine or R(2)-bpy, where R = COOEt or OMe) were synthesized and tested as precatalysts for the hydrogenative reduction of CO(2) in 2,2,2-trifluoroethanol (TFE) as solvent with added NEt(3). Significant amounts of formic acid were produced by these catalysts and a kinetic analysis based on initial rate constants was carried out. The potential mechanisms including intermediate species for these catalytic systems were investigated by means of quantum chemical calculations to gain deeper insight into the processes. The effect of electron-donating and electron-withdrawing groups on catalyst performance was studied both experimentally and theoretically.     

Molecular complexes of sulfur dioxide with organic carbonates

Spectroscopic studies made on the bisphenol A polycarbonate–sulfur dioxide system showed evidence of interaction between polymer and penetrant. Equilibrium studies made on solutions of sulfur dioxide and organic carbonates chosen as monomer analogs showed that complexes of the donor–acceptor type were formed, and that at temperatures of 15°C and less the stoichiometry of these was greater than 1:1. The procedures described are compared with those used in other donor–acceptor studies, and the results observed from the equilibrium studies are interpreted by using data reported for other sulfur dioxide–donor systems.     

Preparation, separation, and characterization of ruthenium(II) thiocyanate linkage isomers

The reaction of [(p-cym)Ru(bpy)Cl](+) (p-cym = eta(6)-p-cymene; bpy = 2,2'-bipyridine) with SCN(-) gives a mixture of the linkage isomers [(p-cym)Ru(bpy)(SCN)](+) and [(p-cym)Ru(bpy)(NCS)](+). The linkage isomers were efficiently separated by column chromatography on Hg(NO3)2-coated Al2O3. Both isomers were fully characterized by elemental analysis, (1)H NMR and IR spectroscopy, and X-ray crystallography. The equilibrium constant for the conversion of the S-bound to the N-bound isomer was determined to be 0.29(4) in methanol-d4 and 0.74(7) in acetone-d6, respectively, at 50 degrees C. Kinetic data for the linkage isomerization reaction are also reported.     

New isomers of 4,1-benzothiazepines. The first evidence for the desmotropy of seven-membered heterocycles

A novel procedure was developed for the preparation of 2,3-disubstituted 4,1-benzothiazepines, via the ring transformation of (2R^∗,2aS^∗)-2-chloro-2a-phenyl-2,2a-dihydro-2H,4H-azeto[1,2-a][3,1]benzothiazin-1-one (1) with sodium ethoxide in ethanol. The tautomeric products (R^∗)-3-ethoxycarbonyl-2-phenyl-3,5-dihydro-4,1-benzothiazepine (4) and 3-ethoxycarbonyl-2-phenyl-1,5-dihydro-4,1-benzothiazepine (5) exhibit the rare phenomenon of desmotropy of the condensed seven-membered heterocycles. Surprisingly, these desmotropes could be separated by column chromatography. The products are unexpectedly stable in solution and their structures were proved by means of NMR and mass spectrometry.     

功能化MCM-41固载的钌基催化剂上二氧化碳加氢合成甲酸

采用两种方法制备了功能化MCM-41固载的钌基催化剂,并用原子吸收光谱,紫外可见光谱以及红外光谱等手段对其进行表征。结果表明,钌基在功能化MCM-41上顺利固载。将这两种固载的钌基催化剂用于二氧化碳加氢合成甲酸反应,发现在较低反应温度和较低氢分压下,固载的RuCl2(PPh3)3催化剂表现出更高的催化活性,在反应温度80℃,H2分压5MPa, CO2分压8MPa下,甲酸转化数达到1275。固载的RuCl2(PPh3)3催化剂也表现出很好的重复再用性。     

Computational evidence for sulfur participation in the first half-reaction of biotin-catalyzed carboxylations

Sulfur participation during the first half-reaction of biotin-dependent, enzyme-catalyzed carboxylations has been examined by ab initio molecular orbital (MO) calculations. Geometry optimization with the 6-31G¹ basis set on the model biotin structure 6, which contains a methyl in place of the side chain, shows that the highest occupied molecular orbital (HOMO) is localized on sulfur and the HOMO-1 is localized on the ureido moiety. Two modes of distortion of 6 were examined as possible enzymestabilized, transition state-like conformations that might show sulfur-ureido interactions. Puckering of ring-B through the use of a distance constraint between sulfur and the carbonyl carbon was found to be ineffective in establishing orbital overlap between sulfur and the ureido group. Twisting of 6 by constraining the methyl to be more pseudo-equatorial relative to the sulfur containing ring results in a loss of symmetry that allows the sulfur 3p orbital to interact with the orbital on the ureido moiety of A₂-like symmetry in a combined through-bond-through-space fashion. The net result is that in this twisted, transition state-like conformation, the ureido nitrogens now contribute to the HOMO and therefore have a lower ionization potential, which can be equated with increased nucleophilicity. Thus, N1 could be nucleophilic enough to initiate N1-carboxylation prior to N1-proton removal in the first half-reaction in biotin-dependent, enzyme-catalyzed carboxylations.     

Aqueous phase carbon dioxide and bicarbonate hydrogenation catalyzed by cyclopentadienyl ruthenium complexes

The water‐soluble ruthenium(II) complexes [Cp′RuX(PTA)₂]Y and [CpRuCl(PPh₃)(mPTA)]OTf (Cp′ = Cp, Cp*, X = Cl and Y = nil; or X = MeCN and Y = PF₆; PTA = 1,3,5‐triaza‐7‐phosphaadamantane; mPTA = 1‐methyl‐1,3,5‐triaza‐7‐phosphaadamantane) were used as catalyst precursors for the hydrogenation of CO₂ and bicarbonate in aqueous solutions, in the absence of amines or other additives, under relatively mild conditions (100 bar H₂, 30–80 °C), with moderate activities. Kinetic studies showed that the hydrogenation of HCO₃^? proceeds without an induction period, and that the rate strongly depends on the pH of the reaction medium. High‐pressure multinuclear NMR spectroscopy revealed that the ruthenium(II) chloride precursors are quantitatively converted into the corresponding hydrides under H₂ pressure. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis, characterization, and SAMs electroactivity of ruthenium complexes with sulfur containing ligands

The vibrational and ¹H NMR data hints that the coordination of the 2,2′-dithiodipyridine (2-pySS) ligand to the [Ru(CN)₅]³⁻ metal center occurs through the sulfur atom instead of the nitrogen atoms which is usually observed for N-heterocyclic ligands. Electrochemical results show that this coordination mode implies an additional thermodynamic stabilization of the Ru^II over Ru^III oxidation state due to a relative stronger π-back-bonding interaction with the empty low-lying dπ orbitals of the sulfur atom. Computational data reinforce the experimental results showing that the 2-pySS Lewis base centers are located on the sulfur atoms. Ligands containing only sulfur atoms as coordination sites (2,2′-dithiodipyridine N-oxide (2-pySSNO), 1,4-dithiane (1,4-dt), and 2,6-dithiaspiro[3.3]heptane (asp)) were also coordinated to the [Ru(CN)₅]³⁻ metal center to undoubtedly correlate the electrochemical results with the ligand coordination atom. Among the synthesized compounds, the [Ru(CN)₅(1,4-dt)]³⁻ and [Ru(CN)₅(asp)]³⁻ complexes showed to be able to form self-assembled monolayers (SAMs) on gold. These SAMs, which were characterized by SERS (surface-enhanced Raman scattering) spectroscopy, successfully assessed the heterogeneous electron transfer reaction of the cytochrome c metalloprotein in physiological medium.     

Polarization gas sensor for sulfur dioxide

The design principle of a compact gas polarization sensor is described. It was shown that a sensor for sulfur dioxide can be prepared on the basis of polysiloxane layers modified with alkyl amines. To exclude the effect of moisture on the sensor indications, the signal from the sensing element under total reflection conditions at the film-prism interface was measured. The detection limit for sulfur dioxide under these conditions was about 1–2 mg/m³.     

Optical sensors for dissolved sulfur dioxide

Colorimetric sensing membranes for the determination of sulfur dioxide were developed and characterized. These films can be used for sensing trace amounts of sulfur dioxide both in the gas phase and in aqueous solutions. Lipophilic pH indicator ion pairs were immobilized in hydrophobic gas-permeable silicone and phenyl substituted ormosil. On exposure to SO₂ the films undergo a visually detectable color change from blue to yellow. No cross-sensitivity to pH and CO₂ was observed. Response times depend on the thickness of the sensing membranes, the indicator concentration in the film as well as on the respective SO₂ concentration. Membranes with response times of < 1 min (t₉₀) were developed. The sensitivity to sulfur dioxide depends on the pK_a of the indicator. An increase in the pK_a results in a lower detection limit. The new optical SO₂ sensors are chemically and mechanically stable and are easy to manufacture. The storage stability of the membranes is at least 7 months if stored in the dark. Received: 17 December 1997 / Revised: 12 June 1998 / Accepted: 15 June 1998     

Aqueous hydrogenation of carbon dioxide catalysed by water-soluble ruthenium aqua complexes under acidic conditions

Hydrogenation of carbon dioxide (P(H2/CO2)= 5.5/2.5 MPa) into formic acid (HCOOH) under acidic conditions (pH 2.5-5.0) in water has been achieved by using water-soluble ruthenium aqua catalysts [(eta6-C6Me6)RuII(L)(OH2)]SO4 (L = 2,2'-bipyridine or 4,4'-dimethoxy-2,2' bipyridine).     

New bipyridyl/phenanthroline ruthenium(II) and ruthenium(III) complexes possessing acetate appended thioether. Evidence for oxidative linkage isomerization

The acetate bearing dithioether, sodium di(2-carboxymethylsufanyl)maleonitrile, L¹ upon reaction with [Ru^II(bpy)₂Cl₂]·2H₂O, [Ru^II(phen)₂Cl₂]·2H₂O, [Ru^III(bpy)₂Cl₂]⁺ or [Ru^III(phen)₂Cl₂]⁺ in methanol formed complexes of the type [(bpy)₂Ru{S₂(CH₂COO)₂C₂(CN)₂}], (1), [(phen)₂Ru{S₂(CH₂COO)₂C₂(CN)₂}], (2), [(bpy)₂Ru{(OOCCH₂)₂S₂C₂(CN)₂}]⁺, (5) and [(phen)₂Ru{(OOCCH₂)₂S₂C₂(CN)₂}]⁺, (6) respectively. Four other Ru(III) complexes with di(benzylsulfanyl)maleonitrile, L², [(bpy)₂Ru{S₂(PhCH₂)C₂(CN)₂}]³⁺, (7) and [(phen)₂Ru{S₂(PhCH₂)₂C₂(CN)₂}]³⁺, (8), and with acetate, [(bpy)₂Ru(OOCCH₃)₂]⁺, (9) and [(phen)₂Ru(OOCCH₃)₂]⁺, (10) were also synthesized. In the cyclic voltammetry, complexes (1) and (2) exhibited quasireversible oxidation waves at 1.01 and 1.02 V vs. Ag/AgCl over GC electrode in DMF, while the corresponding Ru(III) L¹ complexes (5) and (6) exhibit reversible oxidation at E_1/2 0.59 and 0.58 V, respectively, under identical conditions. This is unlike the voltammetric behavior of the Ru(II) and Ru(III) L² complexes, wherein the complex pairs (3), (7) and (4), (8) exhibited identical voltammograms with single reversible one electron waves at E_1/2 0.98 and 0.92 V, respectively under identical conditions. The voltammograms of Ru(II)-L² complexes (3) and (4) also became irreversible in presence of nearly four molar equivalent of sodium acetate. Hence, the irreversible redox behavior of complexes (1) and (2) has been interpreted in terms of rapid linkage isomerization, i.e. shift in κ²-S,S′ to κ²-O,O′ coordination, following the Ru(II)/Ru(III) electrode process. The electronic spectra of Ru(III)-L¹ complexes (5) and (6) resemble closely with that of (9) and (10) instead of Ru(III)-L² complexes (7) and (8), further supports proposed linkage isomerization. The cationic complexes were obtained as [PF₆]⁻ salts and all compounds were characterized using analytical and spectral (IR, ¹H NMR, UV-vis and mass) data.