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Chapter 1. The relevant background to the project is communicated in addition to the project hypothesis and strategy. Tetrylene-f-element bonded complexes are introduced as compounds of nearly unexplored chemical reactivity and bonding character. The strategy of combining tetrylenes with coordinatively unsaturated f-element precursors is briefly described.Chapter 2. Novel uranium-tetrylene bonded complexes are synthesized by utilization of amidinate-supported silylenes. The solid- and solution-state structures of these compounds are examined by X-ray crystallography, absorption spectroscopy, nuclear magnetic resonance spectroscopy, and variable-temperature magnetometry. The nature of the uranium-silicon interactions is further elucidated by density functional theory methods.Chapter 3. The reactivity of f-element-silylene complexes toward hydrogen gas is reported. Despite showing little evidence for bonding in solution, a uranium-silylene complex rapidly activates hydrogen to yield a dihydrosilane product. Lanthanide analogues to the uranium-silylene complex are much less efficient catalysts, while common main group Lewis acids show no catalytic activity. The mechanisms of both the actinide- and lanthanide-catalyzed reactions are deconvoluted through isotope labeling studies and kinetic and theoretical modeling. Investigation of the uranium-catalyzed pathway reveals that dihydrogen complexation by uranium is accessible and may underpin the particular efficiency of this catalyst.

The hydrogen evolution reaction (HER) has a key role in electrochemical water splitting. Recently a lot of attention has been dedicated to HER from single atom catalysts (SACs). The activity of SACs in HER is usually rationalized or predicted using the original model proposed by Nørskov where the free energy of a H atom adsorbed on an extended metal surface M (formation of an MH intermediate) is used to explain the trends in the exchange current for HER. However, SACs differ substantially from metal surfaces and can be considered analogues of coordination compounds. In coordination chemistry, at variance with metal surfaces, stable dihydride or dihydrogen complexes (HMH) can form. We show that the same can occur on SACs and that the formation of stable HMH intermediates, in addition to the MH one, may change the kinetics of the process. Extending the original kinetic model to the case of two intermediates (MH and HMH), one obtains a three-dimensional volcano plot for the HER on SACs. DFT numerical simulations on 55 models demonstrate that the new kinetic model may lead to completely different conclusions about the activity of SACs in HER. The results are validated against selected experimental cases. The work provides an example of the important analogies between the chemistry of SACs and that of coordination compounds.

Rhodium-alkene complexes of the pincer ligand κ3-C5H3N-2,6-(OPiPr2)2 (PONOP-iPr) have been prepared and structurally characterized: [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; ArF = 3,5-(CF3)2C6H3]. Only one of these, alkene = COD, undergoes a reaction with H2 (1 bar), to form [Rh(PONOP-iPr)(η2-COE)][BArF4] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η2-bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP-iPr)(η2-H2)][BArF4], which has been independently synthesized and undergoes exchange with free H2 on the NMR time scale, as well as with D2 to form free HD. When the H2 addition to [Rh(PONOP-iPr)(η2-ethene)][BArF4] is interrogated using pH2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1H NMR signal for the bound H2 ligand, as well as that for free H2, are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted., η2-Alkene complexes [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene] are reported, for which only the COD complex undergoes significant onward reaction with H2 to form a cyclooctene (COE) complex, the reactivity is which is suggested to be due to intramolecular alkene-assisted reductive elimination. The putative product of H2 addition, [Rh(PONOP-iPr)(η2-H2)][BArF4], is made by an alternative route. Remarkably, enhanced signals for this dihydrogen complex are observed when pH2 is added to [Rh(PONOP-iPr)(η2-ethene)][BArF4], a unique example of the partially negative line-shape effect.

Reversible H2 storage under mild conditions is one of the most important targets in the field of materials chemistry. Dihydrogen complexes are attractive materials for this target because they possess moderate adsorption enthalpy as well as adsorption without cleavage of the H–H bond. In spite of these advantages, H2 adsorption studies of dihydrogen complexes in the solid state are scarce. We herein present H2 adsorption properties of the 16-electron precursor complex ([Mo(PCy3)2(CO)3]) in the solid state synthesized by two procedures. One is the direct synthesis under an Ar atmosphere (1), and the other is removal of the N2-adduct under vacuum (2). 2 showed ideal Langmuir type reversible ad/desorption of H2 above room temperature, whereas 1 showed irreversible adsorption. The adsorption enthalpy of 2 was larger than that in THF solution. Using DFT calculation, this difference was explained by the absence of the agostic interaction in the solid state.

A dynamic frequency shift (DFS) in the 1H NMR resonance of the HD unit of the deuterium-labeled dihydrogen complex [Ru(D)(η2-HD)(P3P3iPr)][BPh4] [P3P3iPr = P(CH2CH2CH2PiPr2)3] has been observed and analyzed. To the best of our knowledge, this is the first demonstration of the DFS for a H-D pair. The observed DFS of the center line relative to the outside lines in the H-D triplet is large, up to ∼11 Hz, because of the short H-D distance encountered in dihydrogen complexes. Analysis of the DFS as a function of the temperature, combined with density-functional-theory-calculated or least-squares-fitted electric-field-gradient (EFG) parameters, suggests an H-D bond length of 0.92-0.94 A. A DFS was also observed in trans-[Fe(η2-HD)(H)(dppe)2]+, suggesting the DFS will be commonplace in dihydrogen complexes if appropriate conditions are employed for its observation. Possible applications of the DFS as a probe of the bond lengths, EFGs, and molecular motion, particularly in inorganic systems, are discussed.

The prototypical reactivity profiles of transition metal dihydrogen complexes (M-H2 ) are well-characterized with respect to oxidative addition (to afford dihydrides, M(H)2 ) and as acids, heterolytically delivering H+ to a base and H- to the metal. In the course of this study we explored plausible alternative pathways for H2 activation, namely direct activation through H-atom or hydride transfer from the σ-H2 adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S= 1/2 and an anionic S=0 Co-H2 adduct, both supported by a trisphosphine borane ligand (P3B ). The thermally stable metalloradical, (P3B )Co(H2 ), serves as a competent precursor for hydrogen atom transfer to t Bu3 ArO⋅ . What is more, its anionic derivative, the dihydrogen complex [(P3B )Co(H2 )]1- , is a competent precursor for hydride transfer to BEt3 , establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M-H2 complexes known.

The Co(−I) dihydrogen complexes, [(η2-H2)CoML]−, where ML is the group 13 metalloligand, N(o-(NCH2PiPr2)C6H4)3M, and M is Al, Ga, or In, were previously reported ( J. Am. Chem. Soc. 2017, 139, 6570...

International audience; On the occasion of Professor Odile Eisenstein's 70th birthday and her stepping down as Associate Editor of ACS Catalysis, we reflect on and highlight her distinguished career in computational chemistry and homogeneous catalysis. In this Account we present selected examples of her early work on the computational understanding of transition metal complexes, the evolution of the field towards the quantitative reproduction of these systems, with a final focus on her specific contributions to important catalytic processes including olefin metathesis, s-bond metathesis, and catalytic oxidations.

Many compounds can be represented well in terms of the two-center–two-electron (2c–2e) bond model. However, it is well-known that this approach has limitations; for example, certain compounds require the use of three-center–two-electron (3c–2e) bonds to provide an adequate description of the bonding. Although a classic example of a compound that features a 3c–2e bond is provided by diborane, B2H6, 3c–2e interactions also feature prominently in transition metal chemistry, as exemplified by bridging hydride compounds, agostic compounds, dihydrogen complexes, and hydrocarbon and silane σ-complexes. In addition to being able to identify the different types of bonds (2c–2e and 3c–2e) present in a molecule, it is essential to be able to utilize these models to evaluate the chemical reasonableness of a molecule by applying the octet and 18-electron rules; however, to do so requires determination of the electron counts of atoms in molecules. Although this is easily achieved for molecules that possess only 2c–2e bonds, the situation is more complex for those that possess 3c–2e bonds. Therefore, this article describes a convenient approach for representing 3c–2e interactions in a manner that facilitates the electron counting procedure for such compounds. In particular, specific attention is devoted to the use of the half-arrow formalism to represent 3c–2e interactions in compounds with bridging hydrogen atoms.

While diamagnetic transition metal complexes that bind and split H2 have been extensively studied, paramagnetic complexes that exhibit this behavior remain rare. The square planar S = 1/2 FeI(P4N2)+ cation (FeI+) reversibly binds H2/D2 in solution, exhibiting an inverse equilibrium isotope effect of KH2/KD2 = 0.58(4) at −5.0 °C. In the presence of excess H2, the dihydrogen complex FeI(H2)+ cleaves H2 at 25 °C in a net hydrogen atom transfer reaction, producing the dihydrogen-hydride trans-FeII(H)(H2)+. The proposed mechanism of H2 splitting involves both intra- and intermolecular steps, resulting in a mixed first- and second-order rate law with respect to initial [FeI+]. The key intermediate is a paramagnetic dihydride complex, trans-FeIII(H)2+, whose weak FeIII–H bond dissociation free energy (calculated BDFE = 44 kcal/mol) leads to bimetallic H–H homolysis, generating trans-FeII(H)(H2)+. Reaction kinetics, thermodynamics, electrochemistry, EPR spectroscopy, and DFT calculations support the proposed mech...

The dihydrogen complex Ru(H2)2H2(P(C5H9)3)2 has been investigated, via ab initio accelerated molecular dynamics, to elucidate the H ligands dynamics and possible reaction paths for H2/H exchange. We have characterized the free energy landscape associated with the H atoms positional exchange around the Ru centre. From the free energy landscape, we have been able to estimate a barrier of 6 kcal mol-1 for the H2/H exchange process. We have also observed a trihydrogen intermediate as a passing state along some of the possible reaction pathways.

The loss of the dihydrogen ligand from trans-[Ru(H2)H(dppe)2]+ cations (dppe = PPh2CH2CH2PPh2) in the solid state was investigated using 31P CP/MAS NMR spectroscopy and single crystal X-ray diffraction. While facile dihydrogen loss was observed at room temperature from crystalline samples with the large counteranions BPh4− and B(ArF)4−, ArF = 3,5-C6H3(CF3)2, it only occurred upon heating from complexes with the smaller anions BF4− and PF6−, resulting in the loss of crystallinity. Single crystal X-ray diffraction studies of the new complexes [RuH(dppe)2]BPh4 and trans-[Ru(H2)H(dppe)2]BArF4 are reported. A comparison of the crystal structures of square pyramidal [RuH(dppe)2]BPh4 and octahedral [Ru(H2)H(dppe)2]BPh4 shows that only minor structural changes occur upon loss of H2 from the crystal.

Outer-sphere radical hydrogenation of olefins proceeds via stepwise hydrogen atom transfer (HAT) from transition metal hydride species to the substrate. Typical catalysts exhibit M-H bonds that are either too weak to efficiently activate H2 or too strong to reduce unactivated olefins. This contribution evaluates an alternative approach, that starts from a square-planar cobalt(II) hydride complex. Photoactivation results in Co-H bond homolysis. The three-coordinate cobalt(I) photoproduct binds H2 to give a dihydrogen complex, which is a strong hydrogen atom donor, enabling the stepwise hydrogenation of both styrenes and unactivated aliphatic olefins with H2 via HAT.

The mechanistic insights into hydrogenations of hex-5-en-2-one, isoprene, and 4-vinylcyclohex-1-ene catalyzed by pincer (MesCCC)Co (Mes = bis(mesityl-benzimidazol-2-ylidene)phenyl) complexes are computationally investigated by using the density functional theory. Different from a previously proposed mechanism with a cobalt dihydrogen complex (MesCCC)Co-H2 as the catalyst, we found that its less stable dihydride isomer, (MesCCC)Co(H)2, is the real catalyst in those catalytic cycles. The generations of final products with H2 cleavages for the formations of C−H bonds are the turnover-limiting steps in all three hydrogenation reactions. We found that the hydrogenation selectivity of different C=C bonds in the same compound is dominated by the steric effects, while the hydrogenation selectivity of C=C and C=O bonds in the same compound could be primarily influenced by the electronic effects. In addition, the observed inhabition of the hydrogenation reactions by excessive addition of PPh3 could be explained by a 15.8 kcal/mol free energy barrier for the dissociation of PPh3 from the precatalyst.

Ambient conditions sorption isotherms of dihydrogen in a series of various levels of Cu-exchanged ZSM-5 zeolites, with two different Si/Al ratios, namely 11.5 and 25, show the presence of different amount of Cu centres able to strongly bind H2. Although the isosteric heats of adsorption derived from these isotherms are rather similar, of the order of 30 kJ/mol H2, Inelastic Neutron Scattering (INS) of adsorbed dihydrogen and Fourier-Transformed Infra-Red (FTIR) spectroscopy measurements of adsorbed CO and NO reveal that copper is encountered in two oxidation states. At least two types of Cu(I) ions are clearly detected as well as some heterogeneity of the Cu(II) species. The number of these Cu species is different in the two investigated ZSM-5 materials and depends on the Cu exchange level. With the aid of DFT model cluster calculations we find that under different coordination environments, determined by the Al distribution, both mono- and divalent Cu ions could bind H2 with a different strength. Unprecedentedly, we found that Cu-ions compensating two Al atoms, i.e. formally Cu(II) species, relatively far apart from each other, may behave very similarly to the monovalent Cu-species or alternatively viewed – as Cu(I) species that compensate for two framework Al-atoms. Such Cu-species also form stable η2 dihydrogen complexes.

Ruthenium hydride complexes bearing an N-heterocyclic carbene ligand RuHCl(CO)(IMes)(PPh3)(L/L')] (L = py, 2; 4Mepy, 3; L' = MeCN, 4; Me3CCN, 5) have been synthesized in high-yields via reaction of RuHCl(CO)(IMes)(PPh3)] (1) with pyridyl ligands L (L = py and 4Mepy) or nitrile ligands L' (L' = MeCN and Me3CCN). The ligands L/L' are labile in all the ruthenium hydride complexes; they can be easily replaced by Lewis bases. The X-ray structures of complexes 2 and 3 show intramolecular pi-pi interactions between the aromatic ring of PPh3, IMes, and pyridyl ligands. The protonation reaction of 2-5 gives the corresponding dihydrogen complexes of the type RuCl(eta(2)-H-2)(CO)(IMes)(PPh3)(L/L')]OTf] complexes (L = py, 6; 4Mepy, 7; L' = MeCN, 8; Me3CCN, 9). In all the dihydrogen complexes, H-H bond distances of eta(2)-H-2 ligand is temperature-dependent 0.98 angstrom to 0.93 angstrom in the temperature range of 183-233 K. Attempts to synthesize analogous ruthenium hydride complexes bearing phosphine ligands resulted in a mixture of cis and trans- RuHCl(CO)(PPh3)(2)(L)] L = py, 10/11 (trans(HCl)/cis(HCl)); 4Mepy, 12/13 (trans(HCl)/cis(HCl))] complexes. A comparative study has been done to get an insight into the temperature-dependent H-H bond distances in complexes 6-8 by synthesizing analogous ruthenium dihydrogen complexes, RuCl(eta(2)-H-2)(CO)(PPh3)(2) (L)](OTf) (L = py, 15; 4Mepy, 17). All the complexes have been characterized using NMR spectroscopy. The X-ray crystal structures of complexes 2, 3, and 12 have also been determined.

The paper presents a brief overview of the role of metal hydride complexes in understanding the dynamics of hydrogen generation in homogeneous water reduction catalysts. In addition, the kinetics of protonation of [Os(phen)2(CO)(H)]+ and the one-electron reduced form of the complex, [Os(phen)(phen−)(CO)(H)], in acetonitrile solution were examined. The monocationic complex reacted with tosylic acid to form a distinct intermediate species which was found to be a dihydrogen complex; this went on to produce hydrogen and the solvento complex. The one-electron reduced complex was prepared by reduction of the photoexcited monocationic complex with the sacrificial donor BIH. Protonation of the reduced complex by tosylic acid occurred with a rate constant approximately 100 million times larger. The results are used to address possible mechanistic pathways of existing homogeneous catalysts.

Altres Ajuts: Xunta de Galicia Programa Investigador Distinguido ED431H 2020/21, Acreditación Centro singular de investigación de Galicia 2019-2022, ED431G 2019/03 Altres ajuts: acords transformatius de la UAB To accurate know the acidity of a dihydrogen molecule coordinated to a transition metal ion in water medium is an issue of interest in many areas, from electrochemistry to enzymes and catalysis. However, experimental determination of this magnitude is challenging, and very few values have been reported. In this article we describe a computational protocol, based on DFT calculations and employing a discrete-continuum solvent representation, to estimate pK of transition metal dihydrogen complexes. In this approach the number of solvent molecules explicitly included in the calculations is determined by the convergence with the solvation Gibbs energy of the proton in the solvent. The approach has been initially validated with experimental data in tetrahydrofuran (THF) solvent. Using (THF) clusters a mean absolute deviation from experiments of only 1.4 pK unit is achieved. In water the convergence is reached with (HO) clusters. Using them in a discrete-continuum model, the pK of twelve dihydrogen complexes experimentally characterized in water have been computed. pK values span a wide range, from 23 to -4, illustrating how coordination to a transition metal modifies the dihydrogen acidity. Decomposition of the ∆G of the acid-base equilibrium in two contributions, one intrinsic to the complex and another one accounting for solvent effects enables a deeper analysis of the dihydrogen acidities.

Dicationic thiolate-bridged diruthenium complexes bearing sterically bulky alkane substituents on the thiolate ligands such as [Cp*Ru(μ-SiPr)2Ru(OH2)Cp*](OTf)2 have been found to work as effective catalysts toward oxidation of molecular dihydrogen into protons and electrons in protic solvents such as water and methanol. DFT calculations indicate that the sterically bulky alkane substituent in the complex plays an important role in facilitating the reaction step of the coordination of molecular dihydrogen.

Addition of high pressures of H2 to five-coordinate [(tBu)4(POCOP)Ir(CO)(H)]OTf [(tBu)4(POCOP) = κ3-C6H3-2,6-(OP(tBu)2)2] complexes results in observation of two new iridium–dihydrogen complexes. If the aryl moiety of the POCOP ligand is substituted with an electron withdrawing protonated dimethylamino group at the para position, hydrogen coordination is enhanced. Five-coordinate Ir–H complexes generated by addition of triflic acid to (tBu)4(POCOP)Ir(CO) species show an Ir–H 1H NMR chemical shift dependence on the number of equivalents of acid present. It is proposed that excess triflic acid in solution facilitates triflate dissociation from iridium, resulting in unsaturated five-coordinate Ir–H complexes. The five-coordinate iridium–hydride complexes were found to catalyze H/D exchange between H2 and CD3OD. The existence of the dihydrogen complexes, as well as isotope exchange reactions, provide evidence for proposed ionic hydrogenation intermediates for glycerol deoxygenation.

New mononuclear complexes of composition [AgL(H 2 O) 2 ]NO 3 ·H 2 O, [MnL 2 Cl(H 2 O)]Cl.3½H 2 O, [CuL 2 Cl 2 ].½H 2 O and [PtLCl 3 (H 2 O)]Cl·2H 2 O {where L was 1-(2-furylmethylene)- N -(3-phenylallylidene) methanamine} were synthesized and characterized by different techniques. From the analytical data, the stoichiometry of the complexes were 1:1 for Ag(I) and Pt(IV) complexes and 1:2 (M:L) for Mn(II) and Cu(II) complexes. Conductance data indicated that all complexes are electrolytic in nature while, Cu(II) complex was non-electrolyte. Spectroscopic data suggested that the ligand behaves as a neutral bidentate ligand towards the central metal ion with azomethine nitrogen and furan oxygen atoms as coordination sites. Tetrahedral structure has been proposed for Ag(I) complex, whereas the other complexes possess six coordinated octahedral geometry. TG–DTG study was done to track the thermal behavior of the complexes and the thermodynamic parameters were computed from the thermal data using Coats - Redfern method. The catalytic activity of the metal complexes was evaluated in the decomposition reaction of hydrogen peroxide at 313–333 K temperature range. The data reveal that metal complexes are effective in catalyzing the hydrogen peroxide decomposition and the decomposition percentage increased with temperature. The agar well diffusion technique was used to test the growth inhibition of the ligand and its complexes against different species of bacteria and fungi. The metal complexes are more potent in inhibiting the growth of microorganisms than the ligand and in some cases, the complexes were closed to and more active than the standard species.

Thiamine metal complexes were synthesized and characterized by elemental analysis, IR, electronic spectra, magnetic susceptibility, ESR spectra of Cu(II) complex and EDX for structural investigation of the complexes to know their geometries and mode of bonding. All the manganese, iron, copper, zinc, tungsten and mercury complexes are with octahedral geometry, while cobalt and nickel complexes are with tetrahedral geometry. The selenium and palladium complexes are with square planner geometry, while vanadium complex with stoichiometry (2:1) is with square pyramidal geometry. The thermal properties of the complexes were examined. The kinetic thermodynamic parameters were estimated from the TGA and DTA curves. Molecular modeling of the ligand and its complexes was performed using PC computer to give extra spot lights on the bonding properties of these compounds. Some theoretical studies were carried out to obtain the charges, bond lengths, bond angles and dihedral angles, energies of highest occupied molecular orbital (EHOMO), energies of lowest unoccupied molecular orbital (ELUMO), the separation energy (ΔE), chemical potential, electronegativity, hardness, softness, ionization potential and electron affinity of the studied ligand and its complexes. Correlation analysis was done to explore the relationships between some different parameters of the studied complexes.

Redox-active ligands bring electron- and proton-transfer reactions to main-group coordination chemistry. In this Forum Article, we demonstrate how ligand pKa values can be used in the design of a reaction mechanism for a ligand-based electron- and proton-transfer pathway, where the ligand retains a negative charge and enables dihydrogen evolution. A bis(pyrazolyl)pyridine ligand, iPrPz2P, reacts with 2 equiv of AlCl3 to afford [(iPrPz2P)AlCl2(THF)][AlCl4] (1). A reaction involving two-electron reduction and single-ligand protonation of 1 affords [(iPrHPz2P–)AlCl2] (2), where each of the electron- and proton-transfer events is ligand-centered. Protonation of 2 would formally close a catalytic cycle for dihydrogen production. At −1.26 V versus SCE, in a 0.3 M Bu4NPF6/tetrahydrofuran solution with salicylic acid or (HNEt3)+ as the source of H+, 1 produced dihydrogen electrocatalytically, according to cyclic voltammetry and controlled potential electrolysis experiments. The mechanism for the reaction is most ...

The current work reports synthesis of metal complexes and mixed ligand complexes of a novel sulfonamide Schiff base ligand (HL) resulted from the condensation of sulfametrole [ N ′ -(4-methoxy-1,2,5-thiadiazol-3-yl]sulfanilamide and acetyl-acetone as a primary ligand and glycine as a secondary ligand. The metal complexes and mixed ligand complexes of HL Schiff base ligand were synthesized and characterized using different physicochemical studies as elemental analyses, mass spectra, conductivity measurement, IR spectra, 1 H NMR spectra, UV–vis Spectra, solid reflectance, magnetic susceptibility, thermal analyses (TGA and DTA) and their microbial and anticancer activities. The spectroscopic data of the complexes suggest their 1:2(L 1 :M) complex structures and 1:2:2(L 1 :L 2 :M) mixed ligand complex structures, where L 1 = HL and L 2 = glycine. Also, the spectroscopic studies suggested the octahedral structure for all complexes. The synthesized Schiff base, its metal and mixed ligand complexes were screened for their bacterial, antifungal and anticancer activity. The activity data show that the metal complexes and mixed ligand complexes exhibited promising microbial and anticancer activities than their parent HL Schiff base ligand, also the data show that the mixed ligand complexes more effective than the metal complexes.

A series of new homobimetallic hydride complexes of ruthenium bearing N-heterocyclic carbene ligand of the type [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (4,4’-bpy = 4,4’-bipyridine) (2), [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyen)] (4,4’-dpyen = 1,2-bis(4-pyridyl)ethylene) (4), and [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-dpyan)] (4,4’-dpyan = 1,2-bis(4-pyridyl)ethane) (5) has been synthesized and characterized starting from [RuHCl(IMes)(PPh3)(CO)] (1). The pyridyl-based ligands, (4,4’-bpy), (4,4’-dpyen), and (4,4’-dpyan) in these complexes act as the bridging ligands between the two ruthenium fragments. The bridging ligand in these bimetallic complexes is very labile. Reaction of these complexes with PMe3 led to extensive substitution of not only the bridging ligand but also the PPh3 ligands. Reaction of complexes 2, 4, and 5 with HOTf at low temperatures result in the formation of the corresponding dihydrogen complexes, [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-bpy)][OTf]2 (9), [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyen)][OTf]2 (10), and [{RuCl(η2-H2)(IMes)(PPh3)(CO)}2(4,4’-dpyan)][OTf]2 (11), respectively. These are the first examples of homobimetallic ruthenium dihydrogen complexes bearing NHC ligands. The intact nature of the H–H bond in these derivatives was established by variable temperature 1H (400 MHz) spin-lattice relaxation time (T1, ms) measurements and from the H, D coupling constants of the corresponding HD isotopomers. The H–H distances (dHH) in these complexes fall in the range 0.95–0.98 A. Hydrogen evolution takes place upon warming the dihydrogen complexes generated at low temperatures, indicating the labile nature of the H2 ligand in these complexes. The X-ray crystal structure of [{RuHCl(IMes)(PPh3)(CO)}2(4,4’-bpy)] complex (2) has been determined.

A 2,6-diformyl-4-methyl phenol based multidentate novel symmetric ligand and it is late first-row transition metal complexes have been prepared. The ligand and metal complexes were characterized by different spectroscopic techniques. The ligand shows a symmetric polydentate coordination mode through the phenoxide bimetallic bridge, two azomethine nitrogen atoms and two carbonyl oxygen atoms. All the complexes appear to be binuclear with octahedral geometry and nonelectrolytic nature. Complexes have shown significant growth inhibitory activity against tested bacterial and fungal strains as compared to that of ligand. The cobalt complex exhibited better antifungal potency than the standard used. Copper complex exhibits good antifungal activity whereas cobalt and zinc complexes are found to be good antibacterial agents. Ligand and complexes have shown excellent anti-tubercular activity and Calf Thymus-DNA cleavage property.

The methyl C H bonds in the dimethylfulvene complex [η5,η1-C5H4C(CH3)2][Ru(CO)2][Ru(CO)4] are known experimentally to be activated by the central Ru2 unit to give the dehydrogenation product [η5,η3-C5H4C(CH2)2][Ru(CO)2][Ru(CO)3]. The mechanistic aspects of this process are explored by a theoretical investigation of the two series of complexes [C5H4C(CH3)2]Ru2(CO)n and [C5H4C(CH2)2]Ru2(CO)n (n = 6, 5, 4). Potential reaction intermediates with agostic hydrogen atoms as well as ruthenium carbonyl hydrides and dihydrogen complexes are found.

Recent studies suggest that graphene decorated with light metal atoms is a feasible alternative for the design of the next generation of hydrogen storage systems, that is, materials which require a gravimetric content of at least 7.5 wt%, and an adsorption energy of 0.2–0.6 eV per H2. We present a first principles study of hydrogen adsorption in titanium, and bimetallic Ti5−xAlx (x = 1–3) and Ti7−xAlx (x = 1–4) clusters supported on graphene. Our results for Ti5, Ti4Al, Ti7, and Ti6Al show that doping titanium clusters with small amounts of aluminum does not influence the cluster stability on graphene, but that notably, it enhances its hydrogen gravimetric content up to 3.2–3.6 wt%. A further increment of the aluminum concentration was found to reduce the cluster stability and to favor hydrogen desorption, as shown by our calculations for supported Ti3Al2, Ti2Al3, TiAl4 and Ti5Al2. An analysis of atomic charges and density of states reveals the role of charge transfer and orbital interactions in the stability of hydride and dihydrogen complexes in the studied systems. Our results support the hypothesis that a controlled introduction of small metal clusters to graphene is a feasible way to enhance its hydrogen gravimetric content, and it opens up the possibility of investigating other binary TMx–Ay (TM = transition metal and A = main group) clusters supported on graphene as promising candidates for hydrogen storage.

The synthesis, characterization and density functional theory calculations of mononuclear Ni and Cu complexes supported by the N,N′-dimethyl-N,N′-bis-(pyridine-2-ylmethyl)-1,2-diaminoethane ligand and its derivatives are reported. The complexes were characterized by X-ray crystallography as well as by UV−visible absorption spectroscopy and EPR spectroscopy. The solid state structure of these coordination complexes revealed that the geometry of the complex depended on the identity of the metal center. Solution phase characterization data are in accord with the solid phase structure, indicating minimal structural changes in solution. Optical spectroscopy revealed that all of the complexes exhibit color owing to d-d transition bands in the visible region. Magnetic parameters obtained from EPR spectroscopy together with other structural data suggest that the Ni(II) complexes are in a pseudo-octahedral geometry and Cu(II) complexes are in a distorted square pyramidal geometry. In order to understand in detail how ligand sterics and electronics affect complex topology detailed computational studies were performed. The series of complexes reported in this article will add significant value in the field of coordination chemistry as Ni(II) and Cu(II) complexes supported by tetradentate pyridyl based ligands are rather scarce.

Ruthenium pincer complex RuHCl(PPh3)(PNP)] (PNP = Me-N(CH2CH2PPh2)(2)) (1) was synthesized by reaction of RuHCl(PPh3)(3) with Me-N(CH2CH2PPh2)(2) and characterized. Abstraction of chloride ligand in complex 1 using NaBA(4)(f) in the presence of small molecules such as N-2, H-2, O-2, and CO resulted in the formation of trans-RuH(L)(PPh3)(PNP)]BAr4f {L = N-2 (2), H-2 (4), O-2 (5), CO (6)} complexes. Complexes 2, 4, 5, and 6 have been characterized by various techniques. The reaction of RuHCl(PPh3)(PNP)] complex with NaBH4 gave a borohydrido complex RuH(eta(1)-BH4)(PPh3)(PNP)] (7) which upon reaction with NEt3 generates a mixture of cis and trans dihydrides RuH2(PPh3)(PNP)] (8). The reaction of dihydride complexes with CO2 leads to the formation of formate complex RuH(eta(1)-HCO2)(PPh3)(PNP)] (9). In addition, dihydrogen complexes Ru(eta(2)-H-2)(L)(PPh3)(PNP)](n+) (L = Cl (10), CO (11)) having different trans donor ligands were synthesized by protonation of trans-RuH(L)(PPh3)(PNP)](n+) {n = 0, L = CI; n = 1, L = CO} complexes with HOTf at low temperature. Complexes I and 6 have been characterized by X-ray crystallography. (C) 2016 Elsevier B.V. All rights reserved.

Supported ionic liquid phase (SILP) catalysis enables a highly efficient, Ru-based, homogeneously catalyzed water-gas shift reaction (WGSR) between 100 °C and 150 °C. The active Ru-complexes have been found to exist in imidazolium chloride melts under operating conditions in a dynamic equilibrium, which is dominated by the [Ru(CO) 3 Cl 3 ] − complex. Herein we present state-of-the-art theoretical calculations to elucidate the reaction mechanism in more detail. We show that the mechanism includes the intermediate formation and degradation of hydrogen chloride, which effectively reduces the high barrier for the formation of the requisite dihydrogen complex. The hypothesis that the rate-limiting step involves water is supported by using D 2 O in continuous catalytic WGSR experiments. The resulting mechanism constitutes a highly competitive alternative to earlier reported generic routes involving nucleophilic addition of hydroxide in the gas phase and in solution.

We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH2 complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without H-H bond are the preferential PtH2 systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H2 molecule is oriented almost perpendicular to the outermost C-Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies. Fil: López Corral, Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Piriz, Sebastián. Universidad de la República; Uruguay Fil: Faccio, Ricardo. Universidad de la República; Uruguay Fil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Avena, Marcelo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Azocarboxamides were used as chelating ligands in ruthenium half-sandwich complexes. The synthesis and characterization of two new complexes with an unprecedented coordination motif are presented together with an in-depth investigation of two recently published complexes. Three different coordination modes of the ligands were realized, as evident by NMR spectroscopy and single-crystal X-ray diffraction. The use of base during the synthesis leads to a coordination of a deprotonated ligand, while the introduction of additional donor atoms results in a noncoordinated amide group. The first systematic experimental (cyclic voltammetry and UV–vis–NIR and EPR spectroelectrochemistry) and theoretical (DFT) investigation of the electronic structure of metal complexes bearing this redox-active ligand class is presented, revealing redox processes with ligand contribution. The absorption spectra and electrochemistry are mainly determined by the protonation state of the ligand. While complexes 2[PF6], 3[PF6], and 4[PF...