Electrocatalytic HER Performance of [FeFe]-Hydrogenase Mimics Bearing M-salen Moieties (M=Zn, Ni, Fe, Mn).

The synthesis and characterization of novel compounds (5-8) as mimetics of [FeFe]-hydrogenase, combining two distinct systems capable of participating in hydrogen evolution reactions (HER): the [(μ-adt)Fe(CO)] fragment and M-salen complexes (salen=N,N'-bis(salicylidene)ethylenediamine) (M=Zn, Ni, Fe, Mn), is reported. These complexes were synthesized in high yields via a three-step procedure from N,N'-bis(4-R-salicylidene)ethanediamine) 4 [R=Fe(CO)(μ-SCH)NCOCHO]. Structural analysis through spectroscopic, spectrometric, and computational (DFT) methods confirmed distorted tetrahedral and square-planar geometries for Zn-salen and Ni-salen complexes (5 and 6) respectively, while complexes Fe-salen 7 and Mn-salen 8 exhibit square-based pyramidal structures typical of Fe(III) and Mn(III) high-spin salen-complexes.

Attaching Metal-Containing Moieties to β-Lactam Antibiotics: The Case of Penicillin and Cephalosporin.

Procedures for the preparation of transition metal complexes having intact bicyclic cepham or penam systems as ligands have been developed. Starting from readily available 4-azido-2-azetidinones, a synthetic approach has been tuned using a copper-catalyzed azide-alkyne cycloaddition between 3-azido-2-azetinones and alkynes, followed by methylation and transmetalation to Au(I) and Ir(III) complexes from the mesoionic carbene Ag(I) complexes. This methodology was applied to 6-azido penam and 7-azido cepham derivatives to build 6-(1,2,3-triazolyl)penam and 7-(1,2,3-triazolyl)cepham proligands, which upon methylation and metalation with Au(I) and Ir(III) complexes yielded products derived from the coordination of the metal to the penam C and cepham C positions, preserving intact the bicyclic structure of the penicillin and cephalosporin scaffolds.

A cross-metathesis approach for polymetallic [FeFe]-hydrogenase mimics.

A method has been developed for synthesizing [FeFe]-Hase mimics with diverse structures and properties, employing cross-metathesis of olefins. Vinylmetallocenes (5 and 6) and vinyl half-sandwich complexes (10 and 11) have been used as cross-metathesis partners with [FeFe]-Hase mimics (4, 8, and 9) bearing a double bond in the moiety attached to the ADT-bridge nitrogen. Electrochemical studies of these complexes, encompassing metallocene-type (7a-b, 12a-b, and 13a-b) as well as half-sandwich derivatives (12c and 13c-d), have demonstrated that the introduction of a redox unit has a marginal impact on the reduction potential of these [FeFe]-Hase mimics.

Synthesis, Structure, and Photophysical Properties of Platinum(II) (,,') Pincer Complexes Derived from Purine Nucleobases†.

The synthesis of a series of Pt{κ-,,'-[L]}X (X = Cl, RC≡C) pincer complexes derived from purine and purine nucleosides is reported. In these complexes, the 6-phenylpurine skeleton provides the ,-cyclometalated fragment, whereas an amine, imine, or pyridine substituent of the phenyl ring supplies the additional '-coordination point to the pincer complex. The purine ,-fragment has two coordination positions with the metal (1 and 7), but the formation of the platinum complexes is totally regioselective.

Heteropolymetallic [FeFe]-Hydrogenase Mimics: Synthesis and Electrochemical Properties.

The synthesis and electrochemical properties of tetranuclear [FeS]-hydrogenase mimic species containing Pt(II), Ni(II), and Ru(II) complexes have been studied. To this end, a new tetranuclear [FeS] complex containing a 5,5'-diisocyanide-2,2'-bipyridine bridging ligand has been designed and coordinated to the metal complexes through the bipyridine moiety. Thus, the tetranuclear [FeS] complex () coordinates to Pt(II), Ni(II) and Ru(II) yielding the corresponding metal complexes.

Role of imine isomerization in the stereocontrol of the Staudinger reaction between ketenes and imines.

Computational-experimental analysis has allowed determining that the stereochemistry of the Staudinger reaction between ketenes and imines is strongly associated with the nature of the imine, which affects the two steps of the reaction. The first step, namely the nucleophilic attack of the sp-hybridized nitrogen atom of the imine on the sp-hybridized carbon atom of the ketene, is affected by the energetically accessible isomerization patterns of the imine. The second step consists of a conrotatory electrocyclization of the zwitterionic intermediate formed in the previous step.

β-Lactam and penicillin substituted mesoionic metal carbene complexes.

1,2,3-Triazolylidene MIC M-complexes (M = Au, Pd, Pt) having 2-azetidinones and penicillin G substituents at the triazole ring were prepared by CuAAC on 2-azetidinones having a terminal alkyne tethered at N1, followed by alkylation of the 1,2,3-triazole ring and transmetallation [Au(I), Pd(II) and Pt(II)]. The Au-MIC complexes efficiently catalyze the regioselective cycloisomerization of enynes, while the Pt-MIC complexes were efficient catalysts in hydrosilylation reactions.

Phosphorescent Ir(III) complexes derived from purine nucleobases.

We report the preparation and the study of new types of neutral and cationic phosphorescent heteroleptic Ir(III) complexes derived from 6-phenylpurine nucleosides and nucleotides. Neutral complexes of general formula Ir(C^N)(acac) 7, and 8a-c (HC^N = 9-substituted-6-phenyl purine) are orange-red emissive upon photoexcitation, with short lifetimes and good quantum yields (0.42-0.

- The Magazine of the Spanish Royal Society of Chemistry.

: is the flagship journal of the Spanish Royal Society of Chemistry (RSEQ). currently publishes different types of articles including essays, interviews, opinion, and review articles written for readers (scientists and teachers) who are not specialists in the field. The journal has a special focus in didactics and history of chemistry.

Electrocatalytic Behavior of Tetrathiafulvalene (TTF) and Extended Tetrathiafulvalene (exTTF) [FeFe] Hydrogenase Mimics.

TTF- and exTTF-containing [(μ-S)Fe(CO)] complexes have been prepared by the photochemical reaction of TTF or exTTF and [(μ-S)Fe(CO)]. These complexes are able to interact with PAHs. In the absence of air and in acid media an electrocatalytic dihydrogen evolution reaction (HER) occurs, similarly to analogous [(μ-S)Fe(CO)] complexes.

Preparation and Degradation of Rhodium and Iridium Diolefin Catalysts for the Acceptorless and Base-Free Dehydrogenation of Secondary Alcohols.

Rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols have been prepared, and their degradation has been investigated, during the study of the reactivity of the dimers [M(μ-Cl)(η-CH)] (M = Rh (), Ir ()) and [M(μ-OH)(η-CH)] (M = Rh (), Ir ()) with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePHI). Complex reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of , the mononuclear derivative RhCl(η-CH){κ- -(HBMePHI)} (), and the binuclear species [RhCl(η-CH)]{μ- , -(HBMePHI)} (). Under the same conditions, complex affords the iridium counterparts IrCl(η-CH){κ- -(HBMePHI)} () and [IrCl(η-CH)]{μ- , -(HBMePHI)} ().

Revisiting the photochemical synthesis of [FeFe]-hydrogenase mimics: reaction optimization, mechanistic study and electrochemical behaviour.

The photoreaction of [(μ-S)Fe(CO)] and alkenes or alkynes has been optimized to readily obtain functionalized [FeFe]-hydrogenase mimics. Irradiation under low CO pressure in THF produces the corresponding photo-adducts in good/acceptable (alkenes/alkynes) yields, with retention of the starting olefin stereochemistry. DFT-calculations provide plausible reaction pathways in both, singlet and triplet states.

Spin-Polarized Electron Transmission in DNA-Like Systems.

The helical distribution of the electronic density in chiral molecules, such as DNA and bacteriorhodopsin, has been suggested to induce a spin-orbit coupling interaction that may lead to the so-called chirality-induced spin selectivity (CISS) effect. Key ingredients for the theoretical modelling are, in this context, the helically shaped potential of the molecule and, concomitantly, a Rashba-like spin-orbit coupling due to the appearance of a magnetic field in the electron reference frame. Symmetries of these models clearly play a crucial role in explaining the observed effect, but a thorough analysis has been largely ignored in the literature.

Triazole-Containing [FeFe] Hydrogenase Mimics: Synthesis and Electrocatalytic Behavior.

Through a Cu-catalyzed Huisgen cycloaddition between terminal alkynes and azides (CuAAC) reaction, azide [(μ-SCH)N(4-NCH)Fe(CO)] has demonstrated to be a robust and versatile reagent able to incorporate the [(μ-SR)Fe(CO)] fragment on a wide range of substrates, ranging from aromatic compounds to nucleosides, metallocenes, or redox and luminescent markers. The [FeFe]/[FeFe] and [FeFe]/[FeFe] reduction potentials of the triazole derivatives prepared are comparable to those of other aminodithiolate (adt) Fe-Fe hydrogenase mimics. The presence of the triazole linker influences the electrochemical behavior of these complexes depending on the strength of the acid employed.

1,2,3-Triazolium-Derived Mesoionic Carbene Ligands Bearing Chiral Sulfur-Based Moieties: Synthesis, Catalytic Properties, and Their Role in Chirality Transfer.

1,2,3-Triazole-derived mesoionic carbenes (MICs) having a chiral sulfur functional group at the C5 position are easily available through a CuAAC between chiral alkynyl sulfoxides and different azides. The MICs form complexes with several metals (Au, Ag, Ir, Rh, and Ru) that are enantiomerically pure. Moreover, enantiomerically pure MIC sulfinilimines are obtained from the corresponding sulfoxide retaining the chirality.

Central (S) to Central (M=Ir, Rh) to Planar (Metallocene, M=Fe, Ru) Chirality Transfer Using Sulfoxide-Substituted Mesoionic Carbene Ligands: Synthesis of Bimetallic Planar Chiral Metallocenes.

Enantiopure bimetallic systems containing three different elements of chirality, namely a main-group-based chiral center (sulfur), a transition-metal chiral center (rhodium or iridium), and a planar chiral element (ferrocene or ruthenocene), have been prepared by a sequence of diastereoselective reactions. The chirality of the chiral sulfur center attached to C-5 of a 1,2,3-triazolylidene mesoionic carbene (MIC) ligand coordinated to a metal (Ir, Rh) was transferred through the formation of bimetallic complexes having a chiral-at-metal center and a planar chiral metallocene by C-H activation of the sandwich moiety (M=Fe, Ru). The sense of the planar chirality formed in this sequence of reactions depended on the nature of the ligands at the metal center of the starting complex.

Two Types of σ-Allenyl Complexes from Reactions of Silylenes and Germylenes with Chromium Fischer Alkynyl(alkoxy)carbenes.

The reactivity of amidinatotetrylenes of the type E(tBu bzm)R (E=Si, Ge; tBu bzm=N,N'-bis(tertbutyl)benzamidinate; R =alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C R }(CO) ] (R =Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C atom (γ-attack), which leads to σ-allenyl complexes in which the original C atom maintains its attachment to the Cr(CO) and OEt groups (compounds 3 ), and (b) attack of the amidinatotetrylene to the C atom (α-attack), which ends in σ-allenyl complexes in which the original C atom is not attached to the metal atom and has been inserted into an E-N bond of the amidinatotetrylene forming an E-C-N-C-N five-membered ring (compounds 4 ). It has been found that compounds 3 are thermodynamically less stable than their corresponding 4 isomers and that some of the former (E=Ge; R =CH SiMe ) can be transformed into the latter upon heating.

Bio-Organometallic Derivatives of Antibacterial Drugs.

Overuse and misuse of antibacterial drugs has resulted in bacteria resistance and in an increase in mortality rates due to bacterial infections. Therefore, there is an imperative necessity of new antibacterial drugs. Bio-organometallic derivatives of antibacterial agents offer an opportunity to discover new active antibacterial drugs.

Unexpected Zwitterionic Allenyls from Silylenes and a Fischer Alkynylcarbene: A Remarkable Silylene-Promoted Rearrangement.

The silylenes Si(tBu bzam)R (tBu bzam=N,N'-bis(tertbutyl)benzamidinate; R=mesityl, CH SiMe ) attack the C atom of the Fischer alkynyl(ethoxy)carbene complex [W(CO) {C(OEt)C Ph}] to give, after a striking rearrangement, zwitterionic σ-allenyl complexes in which the original carbene C atom forms part of the allene C fragment and also of a Si-C-N-C-N five-membered ring after insertion into a Si-N bond of the original amidinatosilylene. These remarkable allenyl products, which contain two stereogenic groups, are selectively formed as single diastereomers.

Reversible Carbene Insertion into a Ge-N Bond and Insights into CO and Carbene Substitution Reactions Involving Amidinatogermylenes and Fischer Carbene Complexes.

The formation of the five-membered-ring germylene complexes [M(CO) {Ge(tBu bzamC(OEt)Me)tBu}] (3 ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu bzam)tBu (1 ) and Fischer carbenes [M(CO) {C(OEt)Me}] (2 ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3 undergo epimerization to an equilibrium mixture of 3 and 3' . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene-Fischer carbene complexes [Cr(CO) {C(OEt)Me}{Ge(tBu bzam)tBu}] (cis-4 and trans-4 ).

Thermally Driven Out-of-Equilibrium Two-Impurity Kondo System.

The archetypal two-impurity Kondo problem in a serially coupled double quantum dot is investigated in the presence of a thermal bias θ. The slave-boson formulation is employed to obtain the nonlinear thermal and thermoelectrical responses. When the Kondo correlations prevail over the antiferromagnetic coupling J between dot spins, we demonstrate that the setup shows negative differential thermal conductance regions behaving as a thermal diode.

Unexpected Reaction Pathways Leading to Thiodiglycol During the Degradation of Long-Chain Sulfur Mustards.

Degradation of long-chain sulfur mustards with various commercial decontaminants unexpectedly forms thiodiglycol (TDG) through unreported reaction pathways. Chemical warfare agents (CWAs) degradation products have to be unambiguously related to their reference compounds in order to fulfill international verification protocols. Thus, the formation of TDG using water-based decontaminants introduces an uncertainty in the origin of this chemical that has been systematically used to unambiguously demonstrate the presence of yperite in environmental and biomedical samples.

Triazole vs. triazolium carbene ligands in the site-selective cyclometallation of o-carboranes by M(iii) (M = Ir, Rh) complexes.

Ir(iii) and Rh(iii)-mediated site-selective cage B-H and C-H bond activation in o-carboranylmethyl derivatives has been achieved. The selectivity of the reaction is related to the electron donating properties of the ligand. 1,2,3-Triazole-derivatives use the N2 position of the triazole ring to direct the selective o-carborane B-H bond activation, whereas the corresponding triazolylidene derivatives lead to the cage C-H bond activation with complete site-selectivity.

How to distinguish between interacting and noninteracting molecules in tunnel junctions.

Recent experiments demonstrate a temperature control of the electric conduction through a ferrocene-based molecular junction. Here we examine the results in view of determining means to distinguish between transport through single-particle molecular levels or via transport channels split by Coulomb repulsion. Both transport mechanisms are similar in molecular junctions given the similarities between molecular intralevel energies and the charging energy.