Browsing by Author "Beerhues, Julia"

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Open Access
The best of both worlds : combining the power of MICs and WCAs to generate stable and crystalline CrI‐tetracarbonyl complexes with π‐accepting ligands
(2023) Bens, Tobias; Walter, Robert R. M.; Beerhues, Julia; Schmitt, Manuel; Krossing, Ingo; Sarkar, Biprajit
Here we present stable and crystalline chromium(I) tetracarbonyl complexes with pyridyl-MIC (MIC=mesoionic carbene) ligands and weakly coordinating anions (WCA=[Al(ORF)4]-, RF=C(CF3)3 and BArF=[B(ArF)4]-, ArF=3,5-(CF3)2C6H3). The complexes were fully characterized via crystallographic, spectroscopic and theoretical methods. The influence of counter anions on the IR and EPR spectroscopic properties of the CrI complexes was investigated, and the electronic innocence versus non-innocence of WCAs was probed. These are the first examples of stable and crystalline [Cr(CO)4]+ complexes with a chelating urn:x-wiley:09476539:media:chem202301205:chem202301205-math-0001 accepting ligand, and the data presented here are of relevance for both the photochemical and the electrochemical properties of these classes of compounds.
Open Access
Directed design of a AuI complex with a reduced mesoionic carbene radical ligand : insights from 1,2,3-triazolylidene selenium adducts and extensive electrochemical investigations
(2021) Beerhues, Julia; Neubrand, Maren; Sobottka, Sebastian; Neuman, Nicolás I.; Aberhan, Hannes; Chandra, Shubhadeep; Sarkar, Biprajit
Carbene‐based radicals are important for both fundamental and applied chemical research. Herein, extensive electrochemical investigations of nine different 1,2,3‐triazolylidene selenium adducts are reported. It is found that the half‐wave potentials of the first reduction of the selones correlate with their calculated LUMO levels and the LUMO levels of the corresponding triazolylidene‐based mesoionic carbenes (MICs). Furthermore, unexpected quasi‐reversibility of the reduction of two triazoline selones, exhibiting comparable reduction potentials, was discovered. Through UV/Vis/NIR and EPR spectroelectrochemical investigations supported by DFT calculations, the radical anion was unambiguously assigned to be triazoline centered. This electrochemical behavior was transferred to a triazolylidene‐type MIC‐gold phenyl complex resulting in a MIC‐radical coordinated AuI species. Apart from UV‐Vis‐NIR and EPR spectroelectrochemical investigations of the reduction, the reduced gold‐coordinated MIC radical complex was also formed in situ in the bulk through chemical reduction. This is the first report of a monodentate triazolylidene‐based MIC ligand that can be reduced to its anion radical in a metal complex. The results presented here provide design principles for stabilizing radicals based on MICs.
Open Access
Isolation, characterization and reactivity of key intermediates relevant to reductive (electro)catalysis with Cp*Rh complexes containing pyridyl‐MIC (MIC=mesoionic carbene) ligands
(2023) Bens, Tobias; Walter, Robert R. M.; Beerhues, Julia; Lücke, Clemens; Gabler, Julia; Sarkar, Biprajit
In recent years, metal complexes of pyridyl‐mesoionic carbene (MIC) ligands have been reported as excellent homogeneous and molecular electrocatalysts. In combination with group 9 metals, such ligands form highly active catalysts for hydrogenation/transfer hydrogenation/hydrosilylation catalysis and electrocatalysts for dihydrogen production. Despite such progress, very little is known about the structural/electrochemical/spectroscopic properties of crucial intermediates for such catalytic reactions with these ligands: solvato complexes, reduced complexes and hydridic species. We present here a comprehensive study involving the isolation, crystallographic characterization, electrochemical/spectroelectrochemical/theoretical investigations, and in‐situ reactivity studies of all the aforementioned crucial intermediates involving Cp*Rh and pyridyl‐MIC ligands. A detailed mechanistic study of the precatalytic activation of [RhCp*] complexes with pyridyl‐MIC ligands is presented. Intriguingly, amphiphilicity of the [RhCp*]‐hydride complexes was observed, displaying the substrate dependent transfer of H+, H or H-. To the best of our knowledge, this study is the first of its kind targeting intermediates and reactive species involving metal complexes of pyridyl‐MIC ligands and investigating the interconversion amongst them.
Open Access
Isomerization reactions in anionic mesoionic carbene-borates and control of properties and reactivities in the resulting CoII complexes through agostic interactions
(2020) Stubbe, Jessica; Neuman, Nicolás I.; McLellan, Ross; Sommer, Michael G.; Nößler, Maite; Beerhues, Julia; Mulvey, Robert E.; Sarkar, Biprajit
We present herein anionic borate‐based bi‐mesoionic carbene compounds of the 1,2,3‐triazol‐4‐ylidene type that undergo C-N isomerization reactions. The isomerized compounds are excellent ligands for CoII centers. Strong agostic interactions with the “C-H”‐groups of the cyclohexyl substituents result in an unusual low‐spin square planar CoII complex, which is unreactive towards external substrates. Such agostic interactions are absent in the complex with phenyl substituents on the borate backbone. This complex displays a high‐spin tetrahedral CoII center, which is reactive towards external substrates including dioxygen. To the best of our knowledge, this is also the first investigation of agostic interactions through single‐crystal EPR spectroscopy. We conclusively show here that the structure and properties of these CoII complexes can be strongly influenced through interactions in the secondary coordination sphere. Additionally, we unravel a unique ligand rearrangement for these classes of anionic mesoionic carbene‐based ligands.
Open Access
Synthesis, characterization, and evaluation of antibacterial activity of ferrocenyl‐1,2,3‐triazoles, triazolium salts, and triazolylidene complexes of gold(i) and silver(i)
(2021) Hoyer, Carolin; Schwerk, Peter; Suntrup, Lisa; Beerhues, Julia; Nössler, Maite; Albold, Uta; Dernedde, Jens; Tedin, Karsten; Sarkar, Biprajit
1,2,3‐triazoles, the corresponding triazolium salts, and the resulting mesoionic carbenes (MICs) of the 1,2,3‐triazol‐5‐ylidene type are at the forefront of contemporary research. In this contribution, we present a comprehensive study involving eight triazoles, seventeen triazolium salts, two silver(i)‐ and four gold(i)‐MIC complexes. The substituents on the N1‐atom of the heterocycles are either ferrocenyl or phenyl and those on the C4‐atom bear various alkyl groups. All the compounds were thoroughly characterized by a combination of multinuclear NMR spectroscopy, ESI‐MS and in many cases through single crystal X‐ray diffraction studies. In the electrochemical analysis, all ferrocenyl‐containing compounds display a ferrocenyl‐based oxidation step. Additionally, in both the triazolium salts, and the respective metal complexes, a ligand centered reduction step is observed. All the complexes were tested for their antibacterial properties against the Gram‐negative bacterial strains Salmonella typhimurium (S. typhimurium) and Escherichia coli (E. coli). Many of the tested compounds display good antibacterial activity against the rather resistant Salmonella strain. To inhibit the growth of E. coli, higher concentrations of the compounds tested were required. A preliminary structure‐activity relationship of this set of compounds is also reported.