Reductive Carbon Materials: Tailoring Chemistry and Electronic Properties to Improve Sodium-Ion Batteries.

The development of versatile strategies for preparing functional carbon materials is essential for advancing a wide range of applications in materials science. Precursor design plays a pivotal role in governing the chemistry and structure of carbon materials for target applications. In this work, we report the synthesis of Meldrum's acid derivatives through Knoevenagel condensation with aromatic heterocycles such as pyrrole, furan, and thiophene, which serve as precursors for carbonaceous materials with tailored chemical and electronic properties.

(Electro)chemical N Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand.

Molybdenum(III) complexes bearing pincer-type ligands are well-known catalysts for N-to-NH reduction. We investigated herein the impact of an anionic PNP pincer-type ligand in a Mo(III) complex on the (electro)chemical N splitting ([MoCl], , H = 2,6-bis((di--butylphosphaneyl)methyl)-pyridin-4-one). The increased electron-donating properties of the anionic ligand should lead to a stronger degree of N activation.

Accumulation of Four Electrons on a Terphenyl (Bis)disulfide.

The activation of N , CO or H O to energy-rich products relies on multi-electron transfer reactions, and consequently it seems desirable to understand the basics of light-driven accumulation of multiple redox equivalents. Most of the previously reported molecular acceptors merely allow the storage of up to two electrons. We report on a terphenyl compound including two disulfide bridges, which undergoes four-electron reduction in two separate electrochemical steps, aided by a combination of potential compression and inversion.

Making and breaking of chemical bonds in single nanoconfined molecules.

Nanoconfinement of catalytically active molecules is a powerful strategy to control their chemical activity; however, the atomic-scale mechanisms are challenging to identify. In the present study, the site-specific reactivity of a model rhenium catalyst is studied on the subnanometer scale for complexes confined within quasi-one-dimensional molecular chains on the Ag(001) surface by scanning tunneling microscopy. Injection of tunneling electrons causes ligand dissociation in single molecules.

Luminescent Iridium Complexes with a Sulfurated Bipyridine Ligand: PCET Thermochemistry of the Disulfide Unit and Photophysical Properties.

Molecular systems combining light harvesting and charge storage are receiving great attention in the context of, for example, artificial photosynthesis and solar fuel generation. As part of ongoing efforts to develop new concepts for photoinduced proton-coupled electron transfer (PCET) reactivities, we report a cyclometallated iridium(III) complex [Ir(ppy)(bpy)](PF) (PF) equipped with our previously developed sulfurated bipyridine ligand bpy. A new one-step synthetic protocol for bpy is developed, starting from commercially available 2,2'-bipyridine, which significantly facilitates the use of this ligand.

Neutral Formazan Ligands Bound to the -(CO)Re(I) Fragment: Structural, Spectroscopic, and Computational Studies.

Metal complexes with ligands that coordinate via the nitrogen atom of azo (N═N) or imino (C═N) groups are of interest due to their π-acceptor properties and redox-active nature, which leads to interesting (opto)electronic properties and reactivity. Here, we describe the synthesis and characterization of rhenium(I) tricarbonyl complexes with neutral ,-bidentate formazans, which possess both N═N and C═N fragments within the ligand backbone (Ar-NH-N═C(R)-N═N-Ar). The compounds were synthesized by reacting equimolar amounts of [ReBr(CO)] and the corresponding neutral formazan.

Halide Effects in Reductive Splitting of Dinitrogen with Rhenium Pincer Complexes.

Transition metal halide complexes are used as precursors for reductive N activation up to full splitting into nitride complexes. Distinct halide effects on the redox properties and yields are frequently observed yet not well understood. Here, an electrochemical and computational examination of reductive N splitting with the rhenium(III) complexes [ReX(PNP)] (PNP = N(CHCHPBu) and X = Cl, Br, I) is presented.

Electrochemical CO Reduction Catalyzed by Binuclear LRe(CO)Cl and LMn(CO)Br Complexes with an Internal Proton Source.

The synthesis of certain commodity chemicals, e.g., methanol and acetic acid, relies on CO, which is currently mainly produced by the combustion of carbon or natural gas.

Redox-Active Heteroatom-Functionalized Polyacetylenes.

The discovery of metallic conductivity in polyacetylene [-HC=CH-] upon doping represents a landmark achievement. However, the insolubility of polyacetylene and a dearth of methods for its chemical modification have limited its widespread use. Here, we employ a ring-opening metathesis polymerization (ROMP) protocol to prepare functionalized polyacetylenes (fPAs) bearing: (1) electron-deficient boryl (-BR ) and phosphoryl (-P(O)R ) side chains; (2) electron-donating amino (-NR ) groups, and (3) ring-fused 1,2,3-triazolium units via strain-promoted Click chemistry.

Renewable resources for sustainable metallaelectro-catalysed C-H activation.

The necessity for more sustainable industrial chemical processes has internationally been agreed upon. During the last decade, the scientific community has responded to this urgent need by developing novel sustainable methodologies targeted at molecular transformations that not only produce reduced amounts of byproducts, but also by the use of cleaner and renewable energy sources. A prime example is the electrochemical functionalization of organic molecules, by which toxic and costly chemicals can be replaced by renewable electricity.

A Bioinspired Disulfide/Dithiol Redox Switch in a Rhenium Complex as Proton, H Atom, and Hydride Transfer Reagent.

The transfer of multiple electrons and protons is of crucial importance in many reactions relevant in biology and chemistry. Natural redox-active cofactors are capable of storing and releasing electrons and protons under relatively mild conditions and thus serve as blueprints for synthetic proton-coupled electron transfer (PCET) reagents. Inspired by the prominence of the 2e/2H disulfide/dithiol couple in biology, we investigate herein the diverse PCET reactivity of a Re complex equipped with a bipyridine ligand featuring a unique SH···S moiety in the backbone.

A Stable Homoleptic Divinyl Tetrelene Series.

The synthesis of the new bulky vinyllithium reagent ( IPr=CH)Li, ( IPr=[(MeCNDipp) C]; Dipp=2,6-iPr C H ) is reported. This vinyllithium precursor was found to act as a general source of the anionic 2σ, 2π-electron donor ligand [ IPr=CH] . Furthermore, a high-yielding route to the degradation-resistant Si precursor IPr⋅SiBr is presented.

A dinuclear rhenium complex in the electrochemically driven homogeneous and heterogeneous H/CO-reduction.

A dinculear Re(CO)3 complex with a proton responsive phenol unit and a pyrene anchor in the ligand backbone was investigated in the electrochemical CO2/H+ conversion in solution and adsorbed on multi walled carbon nanotubes (MWCNT) on an GC electrode surface. The pyrene group unit is introduced at the end of the ligand synthesis via a coupling reaction, which allows for a versatile ligand modification in order to tune the electronic properties or to introduce various anchor groups for heterogenisation at a late stage. The redox chemistry of the pyrene-α-diimine-Re(CO)3 complex, 1, was investigated in N,N-dimethylformamide (dmf), including IR-spectroelectrochemical (IR-SEC) characterisation of the short lived, reduced species.

Chemoselective Electrochemical Hydrogenation of Ketones and Aldehydes with a Well-Defined Base-Metal Catalyst.

Hydrogenation reactions are fundamental functional group transformations in chemical synthesis. Here, we introduce an electrochemical method for the hydrogenation of ketones and aldehydes by in situ formation of a Mn-H species. We utilise protons and electric current as surrogate for H and a base-metal complex to form selectively the alcohols.

(Electro-)chemical Splitting of Dinitrogen with a Rhenium Pincer Complex.

The splitting of N into well-defined terminal nitride complexes is a key reaction for nitrogen fixation at ambient conditions. In continuation of our previous work on rhenium pincer mediated N splitting, nitrogen activation and cleavage upon (electro)chemical reduction of [ReCl(2)] {2 = N(CHCHPBu) } is reported. The electrochemical characterization of [ReCl(2)] and comparison with our previously reported platform [ReCl(1)] {1 = N(CHCHPBu) } provides mechanistic insight to rationalize the dependence of nitride yield on the reductant.

Rhenium Complexes of Pyridyl-Mesoionic Carbenes: Photochemical Properties and Electrocatalytic CO Reduction.

Mesoionic carbenes have found wide use as components of homogeneous catalysts. Recent discoveries have, however, shown that metal complexes of such ligands also have huge potential in photochemical research and in the activation of small molecules. We present here three Re complexes with mesoionic pyridyl-carbene ligands.

Electrochemical and Photophysical Properties of Ruthenium(II) Complexes Equipped with Sulfurated Bipyridine Ligands.

The development of new solar-to-fuel scenarios is of great importance, but the construction of molecular systems that convert sunlight into chemical energy represents a challenge. One specific issue is that the molecular systems have to be able to accumulate redox equivalents to mediate the photodriven transformation of relevant small molecules, which mostly involves the orchestrated transfer of multiple electrons and protons. Disulfide/dithiol interconversions are prominent 2e/2H couples and can play an important role for redox control and charge storage.

The Impact of a Proton Relay in Binuclear α-Diimine-Mn(CO) Complexes on the CO Reduction Catalysis.

Herein, we describe the redox chemistry of bi- and mononuclear α-diimine-Mn(CO) complexes with an internal proton source in close proximity to the metal centers and their catalytic activity in the electrochemically driven CO reduction reactions. In order to address the impact of the two metal sites and of the proton source, we investigate a binuclear complex with phenol moiety, , a binuclear Mn complex with methoxyphenol unit instead, , and the mononuclear analogue with a phenol unit, . Spectroelectrochemical investigation of the complexes in dmf under a nitrogen atmosphere indicates that and undergo a reductive H formation forming [Mn(HL)(CO)Br] and [Mn(HL)(CO)], respectively, which is redox neutral for the complex and equivalent to a deprotonation of the phenol unit.

Are Two Metal Ions Better than One? Mono- and Binuclear α-Diimine-Re(CO) Complexes with Proton-Responsive Ligands in CO Reduction Catalysis.

Here, the reduction chemistry of mono- and binuclear α-diimine-Re(CO) complexes with proton responsive ligands and their application in the electrochemically-driven CO reduction catalysis are presented. The work was aimed to investigate the impact of 1) two metal ions in close proximity and 2) an internal proton source on catalysis. Therefore, three different Re complexes, a binuclear one with a central phenol unit, 3, and two mononuclear, one having a central phenol unit, 1, and one with a methoxy unit, 2, were utilised.

Evidence for a Single Electron Shift in a Lewis Acid-Base Reaction.

The Lewis acid-base reaction between a nucleophilic hafnocene-based germylene and tris-pentafluorophenylborane (B(CF)) to give the conventional B-Ge bonded species in almost quantitative yield is reported. This reaction is surprisingly slow, and during its course, radical intermediates are detected by EPR and UV-vis spectroscopy. This suggests that the reaction is initiated by a single electron-transfer step.

Electrochemical water oxidation using a copper complex.

Herein, we report the application of the mononuclear copper complex 1, [Cu(L)], in electrochemical water oxidation catalysis (L = 1,3-bis(((1-methyl-1H-imidazol-2-yl)methyl)amino)propan-2-ol). The complex exhibits a N donor set consisting of two amine and two imidazole units and a dangling OH unit in close proximity to the copper ion. 1 exhibits a moderate apparent rate constant k of 0.

Mechanism of Chemical and Electrochemical N Splitting by a Rhenium Pincer Complex.

A comprehensive mechanistic study of N activation and splitting into terminal nitride ligands upon reduction of the rhenium dichloride complex [ReCl(PNP)] is presented (PNP = N(CHCHP tBu)). Low-temperature studies using chemical reductants enabled full characterization of the N-bridged intermediate [{(PNP)ClRe}(N)] and kinetic analysis of the N-N bond scission process. Controlled potential electrolysis at room temperature also resulted in formation of the nitride product [Re(N)Cl(PNP)].

2,2'-Bipyridine Equipped with a Disulfide/Dithiol Switch for Coupled Two-Electron and Two-Proton Transfer.

[1,2]Dithiino[4,3-b:5,6-b']dipyridine (1) and its protonated open form 3,3'-dithiol-2,2'-bipyridine (2) were synthesised and their interconversion investigated. The X-ray structure of 2 revealed an anti orientation of the two pyridine units and a zwitterionic form. In depth electrochemical studies in combination with DFT calculations lead to a comprehensive picture of the redox chemistry of 1 in the absence and presence of protons.