Bis[1,3-bis(2-hydroxyphenyl)-1,3-propanedionato]bis(ethanol)zinc(II), C34H34O10Zn

Mr=668.0, triclinic, P1, a=13.028 (2), b=11.872(2), c=10.971(2) A, a=102.28 (1), β = 87.14(1), a=112.53(2)º, V = 1530.6(7)A3, Z = 2, Dx = 1.45 Mg m-3, (Mo Ka)=0.71069 A, µ= 0.889 mm-1, F(000)=696, T=295 K. Final R = 0.06 for 3025 observed reflections. The structure consists of chains of molecules parallel to [011] linked by hydrogen bonds. The Zn2+ ion is surrounded by six O atoms in a distorted octahedral shape. The 1,3-bis(2-hydroxyphenyl)-1,3, propanedionato anions act as bidentate ligands. The six-membered Zn-propanedione rings have half-chair form

Interplay between β-Diimino and β-Diketiminato Ligands in Nickel Complexes Active in the Proton Reduction Reaction

Acord transformatiu CRUE-CSICTwo Ni complexes are reported with κ4-P2N2 β-diimino (BDI) ligands with the general formula [Ni(XBDI)](BF4)2, where BDI is N-(2-(diphenylphosphaneyl)ethyl)-4-((2-(diphenylphosphaneyl)ethyl)imino)pent-2-en-2-amine and X indicates the substituent in the α-carbon intradiimine position, X = H for 1(BF4)2 and X = Ph for 2(BF4)2. Electrochemical analysis together with UV-vis and NMR spectroscopy in acetonitrile and dimethylformamide (DMF) indicates the conversion of the β-diimino complexes 12+ and 22+ to the negatively charged β-diketiminato (BDK) analogues (1-H)+ and (2-H)+ via deprotonation in DMF. Moreover, further electrochemical and spectroscopy evidence indicates that the one-electron-reduced derivatives 1+ and 2+ can also rapidly evolve to the BDK (1-H)+ and (2-H)+, respectively, via hydrogen gas evolution through a bimolecular homolytic pathway. Finally, both complexes are demonstrated to be active for the proton reduction reaction in DMF at Eapp = -1.8 V vs Fc+/0, being the active species the one-electron-reduced derivative 1-H and 2-H

Unravelling the Mechanistic Pathway of the Hydrogen Evolution Reaction Driven by a Cobalt Catalyst

Acord transformatiu CRUE-CSICA cobalt complex bearing a κ-NP ligand is presented (1 or Co(L), where L is (1E,1'E)-1,1'-(pyridine-2,6-diyl)bis(N-(3-(diphenylphosphanyl)propyl)ethan-1-imine). Complex 1 is stable under air at oxidation state Co thanks to the π-acceptor character of the phosphine groups. Electrochemical behavior of 1 reveals a two-electron Co/Co oxidation process and an additional one-electron reduction, which leads to an enhancement in the current due to hydrogen evolution reaction (HER) at E=−1.6 V vs Fc/Fc. In the presence of 1 equiv of bis(trifluoromethane)sulfonimide, 1 forms the cobalt hydride derivative Co(L)-H (2), which has been fully characterized. Further addition of 1 equiv of CoCp* (Cp* is pentamethylcyclopentadienyl) affords the reduced Co(L)-H (2) species, which rapidly forms hydrogen and regenerates the initial Co(L) (1). The spectroscopic characterization of catalytic intermediates together with DFT calculations support an unusual bimolecular homolytic mechanism in the catalytic HER with 1

Synthesis and Isomeric Analysis of RuII Complexes Bearing Pentadentate Scaffolds

A RuII-pentadentate polypyridyl complex [RuII(κ-N5-bpy2PYMe)Cl]+ (1+, bpy2PYMe = 1-(2-pyridyl)-1,1-bis(6-2,2'-bipyridyl)ethane) and its aqua derivative [RuII(κ-N5-bpy2PYMe)(H2O)]2+ (22+) were synthesized and characterized by experimental and computational methods. In MeOH, 1+ exists as two isomers in different proportions, cis (70%) and trans (30%), which are interconverted under thermal and photochemical conditions by a sequence of processes: chlorido decoordination, decoordination/recoordination of a pyridyl group, and chlorido recoordination. Under oxidative conditions in dichloromethane, trans-12+ generates a [RuIII(κ-N4-bpy2PYMe)Cl2]+ intermediate after the exchange of a pyridyl ligand by a Cl- counterion, which explains the trans/cis isomerization observed when the system is taken back to Ru(II). On the contrary, cis-12+ is in direct equilibrium with trans-12+, with absence of the κ-N4-bis-chlorido RuIII-intermediate. All these equilibria were modeled by density functional theory calculations. Interestingly, the aqua derivative is obtained as a pure trans-[RuII(κ-N5-bpy2PYMe)(H2O)]2+ isomer (trans-22+), while the addition of a methyl substituent to a single bpy of the pentadentate ligand leads to the formation of a single cis isomer for both chlorido and aqua derivatives [RuII(κ-N5-bpy(bpyMe)PYMe)Cl]+ (3+) and [RuII(κ-N5-bpy(bpyMe)PYMe)(H2O)]2+ (42+) due to the steric constraints imposed by the modified ligand. This system was also structurally and electrochemically compared to the previously reported [RuII(PY5Me2)X]n+ system (X = Cl, n = 1 (5+); X = H2O, n = 2 (62+)), which also contains a κ-N5-RuII coordination environment, and to the newly synthesized [RuII(PY4Im)X]n+ complexes (X = Cl, n = 1 (7+); X = H2O, n = 2 (82+)), which possess an electron-rich Hκ-N4C-RuII site due to the replacement of a pyridyl group by an imidazolic carbene

Molecular water oxidation mechanisms followed by transition metals : State of the art

One clean alternative to fossil fuels would be to split water using sunlight. However, to achieve this goal, researchers still need to fully understand and control several key chemical reactions. One of them is the catalytic oxidation of water to molecular oxygen, which also occurs at the oxygen evolving center of photosystem II in green plants and algae. Despite its importance for biology and renewable energy, the mechanism of this reaction is not fully understood

Heterogeneous Electrochemical Ammonia Oxidation with a Ru-bda Oligomer Anchored on Graphitic Electrodes via CH−π Interactions

Molecular catalysts can promote ammonia oxidation, providing mechanistic insights into the electrochemical N cycle for a carbon-free fuel economy. We report the ammonia oxidation activity of carbon anodes functionalized with the oligomer {[Ru(bda-κ-NO)(4,4'-bpy)](4,4'-bpy)}, Rubda-10, where bda is [2,2'-bipyridine]-6,6'-dicarboxylate and 4,4'-bpy is 4,4'-bipyridine. Electrocatalytic studies in propylene carbonate demonstrate that the Ru-based hybrid anode used in a 3-electrode configuration transforms NH to N and H in a 1:3 ratio with near-unity faradaic efficiency at an applied potential of 0.1 V vs Fc, reaching turnover numbers of 7500. X-ray absorption spectroscopic analysis after bulk electrolysis confirms the molecular integrity of the catalyst. Based on computational studies together with electrochemical evidence, ammonia nucleophilic attack is proposed as the primary pathway that leads to critical N-N bond formation

Ru-bis(pyridine)pyrazolate (bpp)-Based Water-Oxidation Catalysts Anchored on TiO2 : The Importance of the Nature and Position of the Anchoring Group

Altres ajuts: "La Caixa" foundation; COST actions, CM1202 and CM1205Three distinct functionalisation strategies have been applied to the in, in-[{RuII(trpy)}2(μ-bpp)(H2O)2]3+ (trpy=2,2':6',2''-terpyridine, bpp=bis(pyridine)pyrazolate) water-oxidation catalyst framework to form new derivatives that can adsorb onto titania substrates. Modifications included the addition of sulfonate, carboxylate, and phosphonate anchoring groups to the terpyridine and bis(pyridyl)pyrazolate ligands. The complexes were characterised in solution by using 1D NMR, 2D NMR, and UV/Vis spectroscopic analysis and electrochemical techniques. The complexes were then anchored on TiO2-coated fluorinated tin oxide (FTO) films, and the reactivity of these new materials as water-oxidation catalysts was tested electrochemically through controlled-potential electrolysis (CPE) with oxygen evolution detected by headspace analysis with a Clark electrode. The results obtained highlight the importance of the catalyst orientation with respect to the titania surface in regard to its capacity to catalytically oxidize water to dioxygen

Bis[1,3-bis(2-hydroxyphenyl)-1,3-propanedionato]bis(ethanol)zinc(II), C34H34O10Zn

Mr=668.0, triclinic, P1, a=13.028 (2), b=11.872(2), c=10.971(2) A, a=102.28 (1), β = 87.14(1), a=112.53(2)º, V = 1530.6(7)A3, Z = 2, Dx = 1.45 Mg m-3, (Mo Ka)=0.71069 A, µ= 0.889 mm-1, F(000)=696, T=295 K. Final R = 0.06 for 3025 observed reflections. The structure consists of chains of molecules parallel to [011] linked by hydrogen bonds. The Zn2+ ion is surrounded by six O atoms in a distorted octahedral shape. The 1,3-bis(2-hydroxyphenyl)-1,3, propanedionato anions act as bidentate ligands. The six-membered Zn-propanedione rings have half-chair form

Ruthenium Complexes with Chiral bis-Pinene Ligands : an Array of Subtle Structural Diversity

A new chiral derivative of the N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, Me-pinene[5,6]bpea [(−)-L1], has been prepared from a new aldehyde building block [Me-pinene-aldehyde, (−)-4] arising from the monoterpene chiral pool. The tridentate (−)-L1 ligand has been employed to prepare a new set of Ru-Cl complexes in combination with didentate 2,2'-bipyridine (bpy) with the general formula [RuCl((−)-L1)(bpy)]+. These complexes have been characterized in solution by cyclic voltammetry, UV-vis, and 1D and 2D NMR spectroscopy. Isomeric mixtures of trans,fac-C1a and anti,mer-C1c compounds are formed when (−)-L1 is reacted with a [Ru(bpy)(MeOH)Cl3] precursor. Density functional theory calculations of all of the potential isomers of this reaction have been performed in order to interpret the experimental results in terms of electronic and steric effects and also to unravel the observed isomerization pathway between anti,mer-C1c and trans,fac-C1a

Consecutive Ligand-Based Electron Transfer in New Molecular Copper-Based Water Oxidation Catalysts

Water oxidation to dioxygen is one of the key reactions that need to be mastered for the design of practical devices based on water splitting with sunlight. In this context, water oxidation catalysts based on first-row transition metal complexes are highly desirable due to their low cost and their synthetic versatility and tunability through rational ligand design. A new family of dianionic bpy-amidate ligands of general formula HLN n − (LN is [2,2'-bipyridine]-6,6'-dicarboxamide) substituted with phenyl or naphthyl redox non-innocent moieties is described. A detailed electrochemical analysis of [(L4)Cu] 2− (L4=4,4'-(([2,2'-bipyridine]-6,6'-dicarbonyl)bis(azanediyl))dibenzenesulfonate) at pH 11.6 shows the presence of a large electrocatalytic wave for water oxidation catalysis at an η=830 mV. Combined experimental and computational evidence, support an all ligand-based process with redox events taking place at the aryl-amide groups and at the hydroxido ligands. A family of Cu-based complexes bearing dianionic bpy-amidate ligands have been prepared and characterized by spectroscopic and electrochemical techniques. The new complexes are capable of performing water oxidation catalysis at overpotentials between 557-830 mV pH 11.6. A detailed electrocatalytic study in combination with computational calculations revealed the all ligand-based nature of the electron transfer processes involved in the catalytic cycle