Design of New Bis(1,2,3-triazol-1-yl)methane-Based Nitrogen Ligands: Synthesis and Coordination Chemistry.

The reaction between bis(1,2,3-triazol-1-yl)methane derivatives and nBuLi and various aldehydes, yielded novel neutral ligand precursors incorporating alcohol functional groups. The resulting compounds exhibited distinct characteristics depending on the steric hindrance of the aldehyde employed. In instances where aromatic aldehydes were utilized, functionalization occurred at the methine group bridging both triazole rings. Conversely, the use of pivalic aldehyde prompted functionalization at the C5 position of the triazole ring. These compounds were subsequently employed as ligand precursors in the synthesis of organometallic aluminum and zinc complexes, yielding dinuclear complexes with high efficiency. The structural elucidation of all compounds was accomplished through spectroscopic methods and validated by X-ray crystallography. Preliminary catalytic investigations into the coupling reaction of cyclohexene oxide and CO2 revealed that aluminum and zinc complexes catalyzed the selective formation of polyether and polycarbonate materials, respectively.

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

A method has been developed for synthesizing [FeFe]-H2ase 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]-H2ase 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]-H2ase mimics. The application of this cross-metathesis approach has allowed the synthesis of [FeFe]-H2ase mimics featuring an Ir(III) electrochemical antenna (16-18) as well as systems having an electron-donor-photosensitizer structure (ED-PS) (23). The electrocatalytic properties of these complexes have been elucidated through electrochemical studies.

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

The synthesis of a series of Pt{κ3-N,C,N'-[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 N,C-cyclometalated fragment, whereas an amine, imine, or pyridine substituent of the phenyl ring supplies the additional N'-coordination point to the pincer complex. The purine N,C-fragment has two coordination positions with the metal (N1 and N7), but the formation of the platinum complexes is totally regioselective. Coordination through the N7 position leads to the thermodynamically favored [6.5]-Pt{κ3-N7,C,N'-[L]}X complexes. However, the coordination through the N1 position is preferred by the amino derivatives, leading to the isomeric kinetic [5.5]-Pt{κ3-N1,C,N'-[L]}X complexes. Extension of the reported methodology to complexes having both pincer and acetylide ligands derived from nucleosides allows the preparation of novel heteroleptic bis-nucleoside compounds that could be regarded as organometallic models of Pt-induced interstrand cross-link. Complexes having amine or pyridine arms are green phosphorescence emitters upon photoexcitation at low concentrations in CH2Cl2 solution and in poly(methyl methacrylate) (PMMA) films. They undergo self-quenching at high concentrations due to molecular aggregation. The presence of intermolecular π-π stacking and weak Pt···Pt interactions was also observed in the solid state by X-ray diffraction analysis.

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

The synthesis and electrochemical properties of tetranuclear [Fe2S2]-hydrogenase mimic species containing Pt(II), Ni(II), and Ru(II) complexes have been studied. To this end, a new tetranuclear [Fe2S2] 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 [Fe2S2] complex (6) coordinates to Pt(II), Ni(II) and Ru(II) yielding the corresponding metal complexes. The new metal center in the bipyridine linker modulates the electronic communication between the redox-active [Fe2S2] units. Thus, electrochemical studies and DFT calculations have shown that the presence of metal complexes in the structure strongly affect the electronic communication between the [Fe2S2] centers. In the case of diphosphine platinum compounds 10, the structure of the phosphine ligand plays a crucial role to facilitate or to hinder the electronic communication between [Fe2S2] moieties. Compound 10a, bearing a dppe ligand, shows weak electronic communication (ΔE = 170 mV), whereas the interaction is much weaker in the Pt-dppp derivative 10b (ΔE = 80 mV) and virtually negligible in the Pt-dppf complex 10c. The electronic communication is facilitated by incorporation of a Ru-bis(bipyridine) complex, as observed in the BF4 salt 12 (ΔE = 210 mV) although the reduction of the [FeFe] centers occurs at more negative potentials. Overall, the experimental-computational procedure used in this work allows us to study the electronic interaction between the redox-active centers, which, in turn, can be modulated by a transition metal.

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)2(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 (0.42-0.65) in both PMMA films and 2-MeTHF at room temperature. In turn, cationic complexes [Ir(C^N)2(dtb-bpy)][PF6] 9, 12a and 12c (dtb-bpy = 4,4'-di-tert-butyl-2,2'-dipyridine) are yellow-green emitters with moderate quantum yields (0.24-0.32).

ß-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.

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

TTF- and exTTF-containing [(µ-S2)Fe2(CO)6] complexes have been prepared by the photochemical reaction of TTF or exTTF and [(µ-S2)Fe2(CO)6]. 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-S2)Fe2(CO)6] complexes. However, in the presence of air, the TTF and exTTF organic moieties strongly influence the electrochemistry of these systems. The reported data may be valuable in the design of [FeFe] hydrogenase mimics able to combine the HER properties of the [FeFe] cores with the unique TTF properties.

Anales de Química, la Revista de la Real Sociedad Española de Química - The Magazine of the Spanish Royal Society of Chemistry.

: Anales de Química de la Real Sociedad Española de Química is the flagship journal of the Spanish Royal Society of Chemistry (RSEQ). Anales 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. A substantial part of its content is directed towards high school chemistry teachers. An overview of the history of the journal together with its current activities, as well as a brief history of the RSEQ are presented.

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 sp2-hybridized nitrogen atom of the imine on the sp-hybridized carbon atom of the ketene, is affected by the energetically accessible in situ isomerization patterns of the imine. The second step consists of a conrotatory electrocyclization of the zwitterionic intermediate formed in the previous step. This latter pericyclic step depends on the inward/outward torquoelectronic effects generated by the substituents of the imine. The impact of these factors on the stereochemistry of this reaction has been analyzed kinetically by numerical methods. The results of these simulations are compatible with the experimental results and support these conclusions.

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)(η4-C8H12)]2 (M = Rh (1), Ir (2)) and [M(µ-OH)(η4-C8H12)]2 (M = Rh (3), Ir (4)) with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePHI). Complex 1 reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of 1, the mononuclear derivative RhCl(η4-C8H12){κ1-N py-(HBMePHI)} (5), and the binuclear species [RhCl(η4-C8H12)]2{µ-N py,N py-(HBMePHI)} (6). Under the same conditions, complex 2 affords the iridium counterparts IrCl(η4-C8H12){κ1-N py-(HBMePHI)} (7) and [IrCl(η4-C8H12)]2{µ-N py,N py-(HBMePHI)} (8). In contrast to chloride, one of the hydroxide groups of 3 and 4 promotes the deprotonation of HBMePHI to give [M(η4-C8H12)]2(µ-OH){µ-N py,N iso-(BMePHI)} (M = Rh (9), Ir (10)), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KO t Bu, the [BMePHI]- ligand undergoes three different degradations: alcoholysis of an exocyclic isoindoline-N double bond, alcoholysis of a pyridyl-N bond, and opening of the five-membered ring of the isoindoline core.

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

The photoreaction of [(µ-S)2Fe2(CO)6] 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. The DFT-calculation based in the singlet state is energetically more favorable. The electrochemical behavior of the synthesized compounds is also presented, including studies in acidic media. The electrochemical properties of the products vary in the presence of a double bond (cycloaddition of [(µ-S)2Fe2(CO)6] to alkynes), respect to a single bond (cycloaddition to alkenes).

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

Through a Cu-catalyzed Huisgen cycloaddition between terminal alkynes and azides (CuAAC) reaction, azide [(µ-SCH2)2N(4-N3C6H4)Fe2(CO)6] has demonstrated to be a robust and versatile reagent able to incorporate the [(µ-SR)2Fe2(CO)6] fragment on a wide range of substrates, ranging from aromatic compounds to nucleosides, metallocenes, or redox and luminescent markers. The [FeIFeI]/[Fe0FeI] and [Fe0FeI]/[Fe0Fe0] 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. Through this article, the participation of sulfoxide moieties in different catalytic and chirality transfer processes, as well as in discovering mechanistically new processes will be shown. The role of the sulfur chiral moiety in catalytic cycloisomerization and cycloisomerization-dimerization processes using Au-MIC catalysts is dual. The sulfur functional group either stabilizes intermediates in the catalytic cycle, allowing for the reaction to occur or significantly increases the selectivity of the cyclization processes. 1,2,3-Triazole MICs having chiral sulfoxides at C5 are extremely efficient in preparing chiral at the metal complexes by C-H insertion processes. The chiral at the metal half-sandwich complexes, having the enantiopure sulfur chiral group unaltered, experiences different reactions with complete retention of the configuration. Finally, mechanistically new processes, like the desulfinilation of 1,2,3-triazolium salts in Ag-MIC complexes have been uncovered. These still-nascent classes of compounds will offer opportunities for the discovery of novel catalytic applications and to study new mechanistically sound processes.

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. The configurations of these species were assigned on the basis of a combination of X-ray diffraction and CD measurements. An electrochemical study of these bimetallic complexes in coordinating solvents showed an equilibrium between the cationic complexes and the neutral species. The effect of the half-sandwich moiety on the oxidation potentials of the system is remarkable, producing notable cathodic displacements. DFT calculations support these findings.

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(tBu2 bzm)R1 (E=Si, Ge; tBu2 bzm=N,N'-bis(tertbutyl)benzamidinate; R1 =alkyl or aryl) with the chromium Fischer alkynylcarbene complexes [Cr{C(OEt)C2 R2 }(CO)5 ] (R2 =Ph; ferrocenyl, Fc) has been studied. At room temperature, two different reaction pathways have been identified: (a) attack of the amidinatotetrylene to the alkynyl C2 atom (γ-attack), which leads to σ-allenyl complexes in which the original Ccarbene atom maintains its attachment to the Cr(CO)5 and OEt groups (compounds 3 E - R 1 - R 2 ), and (b) attack of the amidinatotetrylene to the Ccarbene atom (α-attack), which ends in σ-allenyl complexes in which the original Ccarbene 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 E - R 1 - R 2 ). It has been found that compounds 3 E - R 1 - R 2 are thermodynamically less stable than their corresponding 4 E - R 1 - R 2 isomers and that some of the former (E=Ge; R1 =CH2 SiMe3 ) can be transformed into the latter upon heating. At high temperatures (>70 °C) the reactions involving bulky amidinatotetrylenes (R1 =Mes, tBu) end in the carbene-substitution products [Cr{E(tBu2 bzm)R1 }(CO)5 ].

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. These compounds are well-characterized products and, in several examples, their antibacterial activities have been studied. Both inhibition of the antibacterial activity and strong increase in the antibiotic activity of the parent drug have been found. The synthesis of the main classes of bio-organometallic derivatives of these drugs, as well as examples of the use of structure-activity relation (SAR) studies to increase the activity and to understand the mode of action of bio-organometallic antimicrobial peptides (BOAMPs) and platensimicyn bio-organometallic mimics is presented in this article.

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)5 {Ge(tBu2 bzamC(OEt)Me)tBu}] (3M ; M=Cr, W), which occurs readily at room temperature from the germylene Ge(tBu2 bzam)tBu (1tBu ) and Fischer carbenes [M(CO)5 {C(OEt)Me}] (2M ; M=Cr, W), has been found to be reversible. Upon heating at 60 °C, complexes 3M undergo epimerization to an equilibrium mixture of 3M and 3'M . At that temperature, the chromium epimers (but not the tungsten ones) release CO to end in the mixed germylene-Fischer carbene complexes [Cr(CO)4 {C(OEt)Me}{Ge(tBu2 bzam)tBu}] (cis-4Cr and trans-4Cr ). The latter decompose at 120 °C to [Cr(CO)5 {Ge(tBu2 bzam)tBu}] (6Cr ). Because the formation of cis-4Cr and trans-4Cr from 3Cr or 3'Cr requires the presence of free 1tBu and 2Cr in the reaction solutions, the reactions of 1tBu with 2M to give 3M (and 3'M at 60 °C) should be reversible. This proposal has been proven by germylene-exchange crossover reactions in which free 1tBu and [M(CO)5 {Ge(tBu2 bzamC(OEt)Me)CH2 SiMe3 }] (5'M ; M=Cr, W) were formed when complexes 3M were treated at room temperature with the germylene Ge(tBu2 bzam)CH2 SiMe3 (1tmsm ). A clear differential behavior between N-heterocyclic carbenes (NHCs) and amidinatogermylenes (1tBu and 1tmsm ) in their reactivity against group 6 metal Fischer carbene complexes is demonstrated. The higher electron-donor capacity of amidinatogermylenes with respect to NHCs and the bias of the former to get involved in ring expansion processes are responsible for this differential behavior.

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

The silylenes Si(tBu2 bzam)R (tBu2 bzam=N,N'-bis(tertbutyl)benzamidinate; R=mesityl, CH2 SiMe3 ) attack the Ccarbene atom of the Fischer alkynyl(ethoxy)carbene complex [W(CO)5 {C(OEt)C2 Ph}] to give, after a striking rearrangement, zwitterionic σ-allenyl complexes in which the original carbene C atom forms part of the allene C3 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.

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. In this work, we present a study of these symmetries and how they can be exploited to enhance chiral-induced spin selectivity in helical molecular systems.

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. Therefore, these novel and unprecedented degradation pathways will result either in modifications of the international verification protocols for forensic purposes or in the exclusion of TDG as an exclusive marker of yperite.