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In this work, we describe the synthesis of a new N-heterocyclic carbene (NHC) ligand, derived from a hybrid pyrazole-imidazolium scaffold, namely 1-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-3-((S)-1-phenylethyl)-3H-imidazol-2-ylidene (L). This ligand has been used as a stabilizer for the organometallic synthesis of palladium(0) nanoparticles (Pd NPs). L presents a better stabilizing effect than its pre-carbenic HLCl counterpart, allowing the formation of isolated Pd NPs while HLCl yields aggregated ones. Additionally, molecular Pd(ii) coordination compounds of L and HLCl were synthesized and characterized to better understand the coordination modes of these ligands. Both molecular and colloidal Pd systems have been further tested in catalytic C–C coupling processes. Three different types of reactions have been observed depending on the catalytic system: (i) the Suzuki–Miyaura reaction takes place with Pd molecular complexes; (ii) a secondary reaction, the dehalogenation of the substrate, is always detected and (iii) the C–C homocoupling between two molecules of bromoarenes is observed with colloidal catalysts. [ABSTRACT FROM AUTHOR]

A family of new ruthenium complexes containing a combination of polypyridyl and carbene ligands has been prepared and characterized from structural, spectroscopic, and redox viewpoints both experimentally and computationally. Interestingly, a correlation between Δ E1/2, defined as the difference between E1/2(RuIV/III) and E1/2(RuIII/II), and the activity and selectivity of some catalytic oxidation processes has been clearly established. A density functional theory study on the synthesized species has been carried out revealing a correlation between the number of carbene ligands and Δ E1/2, and consequently with the RuIII disproportionation. The reactivity of these complexes has been tested with regard to the electrocatalytic oxidation of benzyl alcohol. [ABSTRACT FROM AUTHOR]

The bis(2-pyridyl)ethylamine (bpea) ligand has been used as a starting material for the synthesis of dinuclear Ru complexes of general formula trans,fac-{[RunX(bpea)]2(μ-bpp)}m+(for X = Cl, n = II, m = 1, trans-RuII-Cl, 1+; for X = OH, n = III, m = 3, trans-RuIII-OH, 23+) where the 3,5-bis(2-pyridyl)pyrazolate anionic ligand (bpp) acts as bridging dinucleating ligand, the bpea ligand coordinates in a facial manner and the monodentate ligands X are situated in a transfashion with regard to one another. These complexes have been characterized in solution by 1D and 2D NMR spectroscopy, UV-vis and electrochemical techniques and in the solid state by X-ray diffraction analysis. The reaction of 1(PF6) with Ag+generates the corresponding solvated complex where the Cl ligand has been removed as insoluble AgCl, followed by the oxidation of Ru(ii) to Ru(iii) to generate the corresponding dinuclear complex trans-RuIII-OH, 2(PF6)3. The latter has been shown to catalytically oxidize water to molecular dioxygen using Ce(iv) as oxidant. Quantitative gas evolution as a function of time has been monitored on line by both manometry and mass spectroscopy (MS) techniques. Relative initial velocities of oxygen formation together with structural considerations rule out an intramolecular O–O bond formation pathway. [ABSTRACT FROM AUTHOR]

In this paper we describe the synthesis of the new mixed-donor ligand 1,8-bis(3 5-dimethyl-1H-pyrazol-1-yl)-3,6-dioxaoctane (L). The complexes [MCl2(L)] (M=ZnII (1), CdII (2), HgII (3), PdII (4), PtII (6), NiII (7)) and [PdCI2(L)]2 (5) were prepared and fully characterized. X-ray crystal structures of complexes 1, 2, 4, 6, and 7 have been determined, The L ligand behaves either as a NN-bidentate (chetate or bridge) and NOON-tetradentate (equatorial or planar) ligand. In these structures, C-H⋯X(X=O, N or Cl/Cl-) intermolecularinteractions have been identified and studied. Moreover, the 113Cd(¹H), 195Pt(¹H), and 199Hg(¹H) NMR spectra were measured to investigate the coordination environment of the metal in solution. Diffusion NMR studies have also been performed to characterize monomeric and dimeric species of PdII. Finally, we have observed that the dimeric complex 5 is converted into the corresponding monomeric complex 4. [ABSTRACT FROM AUTHOR]

Abstract: The novel tetradentate ligand 1,4-bis(4-(4′-methyl)-2,2′-bipyridyl)-2,3-diaza-1,3-butadiene (BBDB) was synthesized and characterized by spectroscopic techniques. New complexes of Re and Ru of formulae: [Re(BBDB)(CO)3(Cl)], [(CH3CN)(CO)3Re(μ-BBDB)Re–(CO)3(CH3CN)]2+, [(bpy)2Ru-(μ-BBDB)Ru(bpy)2]4+, [(NH3)4Ru(μ-BBDB)–Ru(NH3)4]4+ (bpy=2,2′-bipyridine) and complexes of Ru with 4-Me-4′-CO2H-bpy (=4-methyl-4′-carboxylic acid-2,2′-bipyridine) – the hydrolyzed derivative of BBDB – of formulae: [(Ru(4-Me-4′-CO2H-bpy)(bpy)2]2+ and [Ru(4-Me-4′-CO2H-bpy)(CN)4]2− were prepared and characterized by spectroscopic, electrochemical and computational techniques. The disclosed enhanced electronic coupling in the mixed-valent complex with ruthenium ammines can be explained by the electronic delocalization imposed by the C N N C backbone. DFT and TD-DFT calculations can predict the optical properties and electronic structures of the reported complexes and comparisons with calculations performed on previously reported complexes with 4-pyridinaldazine can account for their photophysical behaviour. [Copyright &y& Elsevier]

We report in this work the synthesis and spectroscopic, electrochemical, spectroelectrochemical, and photophysical characterization of a novel series of ruthenium polypyridyl complexes with 4-methyl-2,2'-bipyridine-4'-carbonitrile (Mebpy-CN) as an auxiliary ligand of general formula [Ru(bpy)3-x(Mebpy-CN)x(PF6)2 (x = 1-3) (with bpy = 2,2'-bipyridine). A significant increase in the lifetime and quantum yield of emission of the lowest ³MLCT excited state is disclosed when going from x = 1 to x = 3, evidencing an improvement of the photosensitizing properties with respect to [Ru(bpy)3]-(PF6)2. Furthermore, quenching by molecular oxygen of ³MLCT excited states of the three complexes produced singlet molecular oxygen (¹O2) with quantum yield values higher than that of [Ru(bpy)3]2+ in CH3CN. The structure of the complex with x = 1 has been determined by X-ray diffraction. The photoconductivity of ZnO nanowires covered with this same complex is increased by an order of magnitude, pointing to its feasibility as a component of a DSSC. A new dinuclear complex with Mebpy-CN as a bridging ligand has also been prepared and characterized by physicochemical techniques. The derived mixed-valent species of formula [(bpy)2RuII(Mebpy-CN)RuIII(NH3)5]5+ displays a considerable metal--metal electronic coupling due to the derealization effect of a nitrile group in the 4' position of the bpy ring. [ABSTRACT FROM AUTHOR]

The versatility of N-pyrazole, P-phosphinite hybrid ligands [2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyldiphenylphosphinite(L1), 3-(3,5-dimethyl-1H-pyrazol-1-yl)propyldiphenylphosphinite (L2), and 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyldiphenylphosphinite (L3)] has been studied toward Pd(II). The reactions leadto a mixture of three complexes in solution for each ligand ([PdCl2(Lx)],[PdCl2(Lx)2] and [PdCl2(Lx)]2) obtaining monomers(where Lacts as mono-/bidentated agents) and dimerswhere the two Lbridge the two metallic atoms in a head-to-tailarrangement. Complexes have been isolated and fully characterizedby analytical and spectroscopic methods. X-ray crystal structuresof some of the complexes as well as of other species [PdCl2L3]2(only detectedin the solid state) are presented. Furthermore, these complexes wereprepared to examine the effects of the Lstructure onthe topology and interpenetration form (one-dimensional chain, two-dimensionallayer polymers and three-dimensional networks). Additionally, experimentaland simulated NMR studies and a battery of modifications in the synthesisof the complexes (relation ratio of the starting products, order ofaddition, solvents and temperature) permit a better understandingof the role of ligands in the self-assembly process. [ABSTRACT FROM AUTHOR]

The synthesis of a family of new Ru complexes containing the facial tridentate ligand with general formula [RuII(T)(D)(X)]n+ (T = trispyrazolylmethane (tpm); D = ((4S,4′S)-(-)-4,4′,5,5′-tetrahydro-4,4′-bis(1-methylethyl)-2,2′-bioxazole) (iPr-box-C) or N-(1-hydroxy-3-methylbutan-(2S)-(-)-2-yl)-(4S)-(-)-4-isopropyl-4,5-dihydrooxazole-2-carbimidate (iPr-box-O); X = Cl, H2O) has been described. All complexes have been spectroscopically characterized in solution through ¹H NMR and UV-vis techniques, and the redox properties of complexes have also been studied by means of cyclic voltammetry (CV). Furthermore, the chloro complexes presented here have been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic iPr-box-C ligand undergoes a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic ligand iPr-box-O, that keeps coordinated to the Ru metal center and that produces a strong σ-donation effect over it. The reactivity of the Ru-OH2 complexes described in this paper together with other similar ones, previously synthesized by us, has been tested with regard to the epoxidation of different olefins. Complexes [RuII(R-box-C)(tpm)OH2](BF4)2, R = Bz, 3′c/iPr, 3c, show high stereoselectivity in the epoxidation of cis-β-methylstyrene, with the exclusive formation of the cis-epoxide. However, there is a significant difference in regioselectivity between the two catalysts in the epoxidation of 4-vinylcyclohexene; complex 3′c leads to the regioselective oxidation at the ring alkene position, whereas complex 3c leads to the oxidation at the terminal position. Computational calculations indicate only small energy differences between the two possible products of 4-vinylcyclohexene epoxidation, but the energy barriers for the interaction of the catalytic systems with the alkene groups of 4-vinylcyclohexene agree with the reactivity differences found for the two catalysts having isopropyl or benzyl as substituent of the oxazole ligand. Computed local Fukui functions help to explain the observed reactivity trends. [ABSTRACT FROM AUTHOR]

The synthesis of a family of new Ru complexes containing the meddional trpy ligand with general formula [RuII(l)- (D)(X)/1+(1 = 2,2':6',2"-terpyridine (trpy); D = 3,5-dimethyt-2-(2-pyridyl)pyrrolate (pyrpy), and 2-(1-Methyl-3-pyrazo- lyl)pyridine (pypz-Me); X = Cl, H2O) have been described. All complexes have been spectroscopically charactedzed in sotution through 1H NMR and UV-vis techniques, and the chloro complexes have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The pyrpy ligand undergoes an oxidation at the 3-position of the pyrrolate ring during the formation of the corresponding aqua complex thus generating the analogous compound containing the oxidized ligand pyrpy-O. The redox properties of all complexes have also been studied by means of CV and OPV techniques, where both geometrical (trans vs cis) and electronic (neutral vs anionic) effects can be unveiled and rationalized. Finally, the reactivity of the whole set of Ru-OH2 complexes has been tested with regard to the epoxidation of different alkenes with Phl(OAc)2. In all cases good selectivities and conversions were obtained. Furthermore, total retention of the initial cis configuration was achieved when using these catalysts to epoxidize cis-β-methylstyrene. [ABSTRACT FROM AUTHOR]

Three new 3,5-dimethylpyrazolic hybrid ligands N1-substituted by polyether chains and phenyl groups have been synthesized: 1,2-bis[4-(3,5-dimethyl-1H-pyrazol-1-yI)-2-oxabutyl]benzene (Li), 1,3-bis[4-(3,5-dimethyl-1 H-pyrazol-1 - yl)-2-oxabutyl]benzene (L2), and 1 ,4-bis[4-(3,5-dimethyl-1 H-pyrazol-1 -yl)-2-oxabutyl]benzene (L3). The reaction of these ligands with [PdCI2(CH3CN)2] gives two kinds of complexes, monomer or dimer, depending on the solvent. Monomeric chelated complexes [PdCI2(L)] [L = L1 (1), L2 (2), L3 (3)] are obtained when the solvent of the reaction is acetonitrile, whereas when the reaction takes place in tetrahydrofuran binuclear compounds [PdCI2(L)]2 [L = L1 (4), L2 (5), L3 (6)] are formed. The solid-state structures for i and 4 were determined by single-crystal X-ray diffraction methods. All of the palladium(ll) complexes 1-6 were isolated and fully characterized. Diffusion NMR studies have been performed to characterize monomeric and dimeric species in solution. Dimeric compounds present complex 1H NMR spectra, especially 4. Theoretical calculations on this molecule suggest that it is due to the coexistence of different conformers that do not interconvert to each other at room temperature. Finally, it has been observed that dimers are converted into the corresponding monomers in an acetonitrile ref lux, thus indicating that the latter are thermodynamically more stable than dimers. [ABSTRACT FROM AUTHOR]

A new set of Ru-Cl complexes containing either the pinene[5,6]bpea ligand (Li) or the C3 symmetric pinene[4,5]tpmOMe (L2) tridentate ligand in combination with the bidentate (B) 2,2′-bipyridine (bpy) or 1,2-diphenylphosphinoethane (dppe) with general formula [RuCl(L1 or L2)(B)]+ have been prepared and thoroughly characterized. In the solid state, X-ray diffraction analysis techniques have been used. In solution, cyclic voltammetry (CV) and 1 D and 2D NMR spectroscopy have been employed. DFT calculations have been also performed on these complexes and their achiral analogues previously reported in our group, to interpret and complement experimental results. Whereas isomerically pure complexes ([RuIICl(L2)(bpy)](BF4), 5 and [RuIICl(L2)(dppe)](BF4), 6) are obtained when starting from the highly symmetric [RuIIICl3(L2)], 2, isomeric mixtures of cis,fac-[RuIICl(L1)(bpy)](BF4) (3b/3b′), trans,fac- (3a) and up/down,mer- (3c, 3d) isomers are formed when bpy is added to the less symmetric [RuIIICl3(L1)], 1, in contrast to the case of the bulky dppe ligand that, upon coordination to 1, leads to the trans,fac-[RuIICl(L1)(dppe)](BF4) (4a) complex as a sole isomer due to steric factors. [ABSTRACT FROM AUTHOR]

The synthesis of a family of new Ru complexes containing meridional or facial tridentate ligands with the general formula [RuII(T)(D)(X)]n+ [T = 2,2′:6′,2″-terpyridine or tripyrazolylmethane; D = 4,4′-dibenzyl-4,4′,5,5′-tetrahydro-2,2′-bioxazole (S,S-box-C) or 2-[((1′S)-1′-(hydroxymethyl)-2′-phenyl)ethylcarboxamide}-(4S)-4-benzyl-4,5-dihydrooxazole (S,S-box-O); X = Cl, H2O, MeCN or pyridine] has been described. All complexes have been spectroscopically characterized in solution through ¹H NMR and UV-vis techniques. Furthermore, all of the chloro complexes presented here have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic S,S-box-C ligands undergo a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic oxazolinic ligands S,S-box-O, which are also strongly attached to the metal center and produce a strong σ-donation effect over the Ru metal center. The redox properties of all complexes have also been studied by means of cyclic voltammetry, strongly reflecting the nature of the ligands; both effects, geometrical (facial vs meridional) and electronic (neutral vs anionic), can be unveiled and rationalized. Finally, the reactivity of the Ru-OH2 complexes has been tested with regard to the epoxidation of trans-stilbene, and it has been shown that, in this particular case, the reactivity is practically not dependent on the redox potentials of the catalyst but, in sharp contrast, it is strongly dependent on the geometry of the tridentate ligands. [ABSTRACT FROM AUTHOR]

The synthesis and isolation of the complex cis,fac-[RuIICl2(bpea)(PPh3)] [3; bpea = N,N-bis(2-pyridylmethyl)ethylamine] and three geometrical isomers of the complex [RuIICl(bpea)(dppe)](BF4) [4; dppe = (1,2-diphenylphosphino)ethanel, trans,fac (4a), cis,fac (4b), and mer(down) (4c), have been described (see Chart 1 for a drawing of their structures). These complexes have been characterized through analytical, spectroscopic (IR, UV/vis, and 1D and 2D NMR), and electrochemical (cyclic voltammetry) techniques. In addition, complexes 3, 4a, and 4b have been further characterized in the solid state through monocrystal X-ray diffraction analysis. The molecular and electronic structures of isomers 4a, 4b, 4c, and 4d (the mer(up) isomer) have also been studied by means of density functional theory (DFT) calculations. Furthermore, their low-energy electronic transitions have been simulated using time-dependent DFT approaches, which have allowed unraveling of their metal-to-ligand charge-transfer nature. Complexes 3 and 4a-c are capable of catalyzing H-transfer types of reactions between alcohols and aromatic ketones such as acetophenone and 2,2-dimethylpropiophenone (DP). A strong influence of the facial versus meridional geometry in the bpea ligand coordination mode is observed for these catalytic reactions, with the meridional isomer being much more active than the facial one. The meridional isomer is even capable of carrying out the H-transfer reaction of bulky substrates such as DP at room temperature. [ABSTRACT FROM AUTHOR]

New polypyridylic chiral ligands, having either C3 or lower symmetry, have been prepared via a de novo construction of the pyridine nucleus by means of Kröhnke methodology in the key step. The chiral moieties of these ligands originate from the monoterpen chiral pool, namely (-)-α-pinene ((-)-14, (-)-15) and (-)-myrtenal ((-)-9, (-)-10). Extension of the above-mentioned asymmetric synthesis procedure to the preparation of enantiopure derivatives of some commonly used polypyridylic ligands has been achieved through a new aldehyde building block ((-)-16). As an example, the synthesis of a chiral derivative of N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, (-)-19, has been performed to illustrate the viability of the method. The coordinative ability of the ligands has been tested through the synthesis and characterization of complexes [Mn((-)-19)Br2], (-)-20, and [RuCl((-)-10)(bpy)](BF4), (-)-21. Some preliminary results related to the enantioselective catalytic epoxidation of styrene with the ruthenium complex are also presented.; [ABSTRACT FROM AUTHOR]

The crystal structure of 3,7,11,18,22,26-hexaazatricyclo[26.2.2.2[sup13,16]]tetratriaconta-1(31),13(34),14,16(33),28(32),-29-hexaene hexahydrobromide salt [(H[sub6]P3)Br[sub6]] has been determined by means of X-ray diffraction analysis. It crystallizes with an additional molecule of ethanol and half a molecule of water per molecule of the hydrobromide P3 ligand. The protonation constants of P3 and its host-guest interactions with monophospate (Ph) and pyrophosphate (Pp) have been investigated by potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic interactions between the host and the guest; formation constants for all the species obtained are reported and compared with the isomeric 3,7,11,19,23,27-hexaazatricyclo[27.3.1.1[sup13,17]]tetratriaconta-1(33),13,15,17(34),29,31-hexaene (Bn) ligand. For the H[sub6]P3Pp[sup2+] those bonding interactions reach a maximum yielding a log K[supR],[sub6] of 5.87. The selectivity of the P3 ligand with regard to the monophosphate and pyrophosphate substrates (S) is discussed and illustrated with global species distribution diagrams showing a strong preference for the latter over the former as a consequence of the much stronger formation constants with pyrophosphate. An analysis of the isomeric effect is also carried out by comparing the P3-S versus Bn-S systems. in the best case, a selectivity of over 88% is achieved for the diphosphate complexation when using the meta isomer over the para, due solely to the size and shape of the receptors cavity. [ABSTRACT FROM AUTHOR]

Three pairs of mononuclear geometrical isomers containing the ligand 3,5-bis(2-pyridyl)pyrazole (Hbpp) of general formula in- and out-[Ru[supII](Hbpp)(trpy)X][supn+] (trpy = 2,2':6',2"-terpyridine; X = Cl, n = 1, 2a,b; X = H[sub2]O, n = 2, 3a,b; X = py (pyridine), n = 2, 4a,b) have been prepared through two different synthetic routes, isolated, and structurally characterized. The solid state structural characterization was performed by X-ray diffraction analysis of four complexes: 2a-4a and 4b. The structural characterization in solution was performed by means of 1D and 2D NMR spectroscopy for complexes 2a,b and 4a,b and coincides with the structures found in the solid state. All complexes were also spectroscopically characterized by UV-vis which also allowed us to carry out spectrophotometric acid-base titrations. Thus, a number of species were spectroscopically characterized with the same oxidation state but with a different degree of protonation. As an example, for 3a three pK[suba] values were obtained: pK[suba1](Ru[supII]) = 2.13, pK[suba2](Ru[supII]) = 6.88, and pK[suba3](Ru[supII]) = 11.09. The redox properties were also studied, giving in all cases a number of electron transfers coupled to proton transfers. The pH dependency of the redox potentials allowed us to calculate the pK[suba] of the complexes in the Ru(III) oxidation state. For complex 3a, these were found to be pK[suba1](Ru[supIII]) = 0.01, pK[suba2](Ru[supIII]) = 2.78, and pK[suba3](Ru[supIII]) = 5.43. The oxidation state Ru(IV) was only reached from the Ru-OH[sub2] type of complexes 3a or 3b. It has also been shown that the Ru[supIV]=O species derived from 3a is capable of electrocatalytically oxidizing benzyl alcohol with a second-order rate constant of k[subcat] = 17.1 M[sup-1] s[sup-1]. [ABSTRACT FROM AUTHOR]

The synthesis and structural and spectroscopic characterization of a family of copper(I) complexes, containing a dinucleating hexaaza macrocyclic ligand, of general formula [Cu[sub 2](L)(X)[sub 2]][sup 2+] (L = Me2p, Me2m, Me3p, or Me3m; X = MeCN, n-PrCN, CQ, t-BuNC, or PPh[sub 3]) is described. This family of complexes contains ligands that differ from one another in the number of methylenic units linking the tertiary amines and in the meta or para substitution of their aromatic rings. The structural characterization in the solid-state includes a single-crystal X-ray diffraction analysis of [Cu[sub 2](Me2p)(CO)[sub 2]][sup 2+] and of [Cu[sub 2](Me2m)(t-BuNC)[sub 2]][sup 2+]. In solution, those complexes are structurally characterized through NMR spectroscopy that also allows us to put forward and establish their fluxional behavior. Theoretical calculations at the DFT level have also been performed. In order to further analyze the relative energy of the different potential isomers as well as to gain insight into their chemical properties. Finally, the influence of the hexaaza ligands over different structural aspects as well as on its potential chemical reactivity is discussed. [ABSTRACT FROM AUTHOR]

Two isomeric Ru(ll) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with CI and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans, cis-[Ru[sup II]CI[sub 2](Hbpp)(dmso)[sub 2]], 2a, and cis(out),cis-[Ru[sup II]Cl[sub 2](Hbpp)(dmso)[sub 2]], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[Ru[sup II[CI[sub 2](Hbpp)(MeCN)(dmso)], 4. While the 1 e[sup -] oxidation of 2b or cis(out),cis-[Ru[sup II]Cl[sub 2](bpp)(dmso)[sub 2]][sup +], 3b, generates a stable product, the same process for 2a or trans, cis-[R[sup II]Cl[sub 2](bpp)(dmso)[sub 2]][sup +], 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (K[sup III, sub O→S] = 0.25 ± 0.025, k[sup III, sub O → S] = 0.017 s[sup -1], and k[sup III, sub S → O] = 0.065 s[sup -1] k[sup II, sub O → S] = 6.45 × 10[sup 9]. k[sup II, sub O → S] = 0.132 s[sup -1], k[sup II, sub S → O] = 2.1 × 10[sup -11] s[sup -1]). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms. [ABSTRACT FROM AUTHOR]

Examines the performance of ruthenium complexes containing the tridentate bpea ligand as redox catalysts by elemental analyses, ultraviolet-visible and nuclear magnetic resonance spectroscopies, and electrochemical studies. Stereoisomeric analysis of complexes; Redox spectrophotometric titration by sequential addition of cerium(IV); Potential/pH regions of stability for oxidation states and their dominant proton compositions.

The article discusses the ligand design discovered by T.J. Meyer which has oxidative properties and its redox potentials that contributes to its reactivity with substrates. It also reports on the disproportionation of its oxidation states which can provide a design for oxidation of organic substrates and energy conversion schemes.