CoII Complexes Research Articles

A trapped hexaaqua CoII complex between the polyanionic sheets of decavanadate reveals high axial anisotropy and field induced SIM behaviour.

In this work, we report an inorganic compound [{Co(H2O)6}2+{Na4V10O28}2-] (1) in which the polyanionic sheets of decavanadate play the role of a diamagnetic matrix that reduces the dipolar-dipolar and spin-spin interactions between [Co(H2O)6]+2 units to suppress the fast tunnelling of magnetization. Structural analysis reveals that each [Co(H2O)6]+2 complex is surrounded by four decavanadates and separated by a large internuclear distance (9 Å). It was also found that the adjacent decavanadates are connected via sodium ions and form a 2D sheet of the inorganic layer in which the [Co(H2O)6]2+ ions are present in between two layers. Detailed dc (direct current) and ac (alternating current) magnetic measurements disclose the presence of large easy-axis anisotropy (D = -102 cm-1) and field induced slow magnetic relaxation behaviour with a spin reversal barrier of Ueff = 50 K. Additionally, the temperature dependence of the relaxation time reveals that the Raman and QTM processes mainly play an important role rather than the thermally activated Orbach process in the overall relaxation dynamics of the studied compound. To analyse the electronic structure and magnetic properties of compound 1, ab initio calculations were performed which further support the experimental observations. Notably, the Ueff value of 1 represents the highest energy barrier reported for POM based SMMs with transition metal ions to date.

Studies on the Spectral, Anti-Bacterial and Anti-Fungal Activities of 1-((Dicyclohexylamino) (Phenyl) Methyl) Pyrrolidine-2, 5-Dione and Few of its Metal Complexes

1-((dicyclohexylamino)(phenyl)methyl) pyrrolidine-2,5-dione (SDB) has been synthesized as a result of succinimide, benzaldehyde and dicyclohexylamine Mannich base condensation and its CoII, NiII and CuII complexes were prepared. The structure of the Mannich Base ligand (SDB) was elucidated on the basis of FT-IR, 1H NMR, 13C NMR and Mass spectral studies. The monomeric and non-electrolytic nature of the metal complexes is evidenced by their magnetic susceptibility and low conductance data studies. Spectral tests, mainly FT-IR studies as well as elemental analysis, were carried out to verify the structures of the newly synthesized compounds. All the metal complexes possess a six-coordinate geometry. The synthesized ligand and its metal complexes have been tested against Gram-positive strains (Staphylococcus aureus and Micrococcus luteus), Gram-negative strains (Escherichia coli and Pseudomonas aeruginosa) and fungal strains (Aspergillus niger and Aspergillus fumigates) for their in vitro anti-bacterial and anti-fungal activities. Preliminary antimicrobial studies of the ligand and their metal complexes have also been carried out in order to understand the toxic effect of ligands and metal complexes against the selective microbes. The results showed that the metal chelates of the ligands showed higher antimicrobial activities than the free ligand SDB and CoII complexes possess higher activity than the other metal complexes.

Activation of Molecular Oxygen by a Cobalt(II) Tetra-NHC Complex*.

The first dicobalt(III) μ 2‐peroxo N‐heterocyclic carbene (NHC) complex is reported. It can be quantitatively generated from a cobalt(II) compound bearing a 16‐membered macrocyclic tetra‐NHC ligand via facile activation of dioxygen from air at ambient conditions. The reaction proceeds via an end‐on superoxo intermediate as demonstrated by EPR studies and DFT. The peroxo moiety can be cleaved upon addition of acetic acid, yielding the corresponding CoIII acetate complex going along with H2O2 formation. In contrast, both CoII and CoIII complexes are also studied as catalysts to utilize air for olefin and alkane oxidation reactions; however, not resulting in product formation. The observations are rationalized by DFT‐calculations, suggesting a nucleophilic nature of the dicobalt(III) μ 2‐peroxo complex. All isolated compounds are characterized by NMR, ESI‐MS, elemental analysis, EPR and SC‐XRD.

Synthesis and characterization of MnII and CoII complexes with poly (vinyl alcohol-nicotinic acid) for photocatalytic degradation of Indigo carmine dye

A suitable process for modifying PVA with nicotinic acid to generate a graft copolymer was developed. The copolymers received as ligand were complexed with MnII and CoII ions. The coordination of this copolymer with the metal ion and the inclusion of nicotinic acid in the PVA copolymer was ascertained by FT-IR and NMR spectroscopy. EPR and UV–vis spectra of complexes indicates that CoII as square planar geometry and MnII as octahedral complexes. The adsorption of IC dye onto CoII/NA-PVA complex was noticeably greater (90%) than MnII/NA-PVA complexes. The DFT quantum chemical calculation was applied against the tested compounds. Optimization geometry and frontier molecular orbitals (FMOs) postulated that the charge transfer occurred from metal to ligands. The calculated NLOs properties for these polymers were higher character than reference material.

Syntheses, crystal structures and antimicrobial activities of polynuclear CoII, NiII and ZnII complexes derived from the N,N'-bis(4-fluorosalicylidene)-1,3-propanediamine Schiff base

A series of new cobalt(II), nickel(II) and zinc(II) complexes [Co{CoL(CH3COO)}2] (1), [Ni{NiL(CH3COO)}2] (2), [Zn{ZnL(CH3COO)}2] (3), [Ni2ClL(μ2-1,5-dca)]n (4), [Zn2BrL(μ1,1-N3)]2 (5), [Zn2ClL(μ1,1-N3)]2 (6), where L is the doubly deprotonated form of N,N'-bis(4-fluorosalicylidene)-1,3-propanediamine (H2L), dca is dicyanoamide, were synthesized and characterized by elemental analyses, infrared and electronic spectroscopy, and single crystal X-ray determination. Complexes 1, 2 and 3 are isostructural acetato- and phenolato-bridged trinuclear compounds. Complex 4 is a μ2-1,5-dca and phenolato-bridged polymeric compound. Complexes 5 and 6 are isostructural end-on azido- and phenolato-bridged tetranuclear compounds. The compounds were evaluated for their antibacterial (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescens) and antifungal (Candida albicans and Aspergillus niger) activities by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) method.

Isomerization Reactions in Anionic Mesoionic Carbene-Borates and Control of Properties and Reactivities in the Resulting CoII Complexes through Agostic Interactions.

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.

Cobalt(III)-Catalyzed Enantioselective Intermolecular Carboamination by C-H Functionalization.

High-valent cyclopentadienyl cobalt catalysis is a versatile tool for sustainable C-H bond functionalizations. To harness the full potential of this strategy, control of the stereoselectivity of these processes is necessary. Herein, we report highly enantioselective intermolecular carboaminations of alkenes through C-H activation of N-phenoxyamides catalyzed by CoIII -complexes equipped with chiral cyclopentadienyl (Cpx ) ligands. The method converts widely available acrylates as well as bicyclic olefins into attractive enantioenriched isotyrosine derivatives as well as elaborated amino-substituted bicyclic scaffolds under very mild conditions. The outlined reactivity is unique to the Cpx CoIII complexes and is complementary to the reactivity of 4d- and 5d- precious-metal catalysts.

Kinetic Study and Nonlinear Phenomenon during the Copolymerization of CO2 with meso‐Epoxides Catalyzed by Various Bimetallic CoIII Complexes

AbstractThe privileged salen ligands coordinated with a metal center have demonstrated their successful applications in many challenging reactions. Moreover, their relatively straightforward preparations and an ease of structural modifications are also very attractive. The CoIII–salen complex has demonstrated to be one of the most efficient catalysts for the copolymerization of CO2 with epoxides. Especially, the elaborate combination of two or more CoIII–salen units into one single molecule may enforce an intramolecular, cooperative reaction pathway, resulting in enhanced reaction rates or/and higher selectivities. Otherwise, the reactivity and/or selectivity will be reduced, or some side reactions may occur. Herein, various bimetallic CoIII complexes based on different linking groups are reported to bridge two salen planes, including flexible and rigid structures, together with their reactivities and selectivities toward copolymerization of CO2 with meso‐epoxides. The asymmetric depletion in copolymerization CO2 with cyclohexene oxide mediated by monometallic CoIII complex 2 is first observed, demonstrating the bimetallic mechanism; especially, the comparative kinetic measurements are performed as a function of reaction temperature to assess the activation barrier for production of copolymers for bi‐ and monometallic CoIII complexes. This study is expected to be instructive and meaningful to design more efficient bimetallic catalyst and to improve the copolymerization selectivity.

Co(cyclam) Complexes of Triarylamine-acetylide: Structural and Spectroscopic Properties and DFT Analysis

Reported herein are the syntheses of mono- and bis-C2TPA (HC2TPA = 4-ethynyl-N,N-bis(4-methoxyphenyl)aniline) complexes of CoIII(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane) complexes, and ...

Template Synthesis, Characterization, Antioxidant Effects, DNA Cleavage and Antimicrobial Studies of ZnII, NiII, MnII, CuII and CoII Complexes Containing Pyridazinone Moiety

Bu çalışmada template metodu ile o-aminofenol, 5-benzoil-4-hidroksi-2-metil-6-fenil-2Hpiridazin-3-on ve ZnII, NiII, MnII, CuII ve CoII metal tuzlarından türeyen beş yeni Schiff baz kompleksi sentezlenmiştir. Metal kompleksler elemental analiz, FT-IR, UV-Vis, kütle ve manyetik duyarlılık ile karakterize edilmiştir. Sentezlenen bileşiklerin antioksidan etkileri, DNA bölünmesi ve antimikrobiyal çalışmaları yapılmıştır. DPPH süpürme ve metal şelatlama aktivitesinin konsantrasyona bağlı olarak arttığı bulunmuştur. En yüksek DPPH aktivitesi ve demir iyon şelatlama aktivitesi Zn bileşiğinden elde edildi. Sentezlenen tüm bileşikler, Mn>Zn=Ni=Co>Cu sırasına gore E. hirae’ye karşı antibakteriyal aktivite sergilerken, sadece Ni bileşiği test edilen tüm organizmalara karşı, özellikle de L. pneumophila subsp. pneumophila’ya 13 mm’ye eşit inhibisyon zon değerinde antimikrobiyal aktivite göstermiştir.

Syntheses, Structures, and Bioactivities Evaluation of some Transition Metal Complexes with 4,4'‐Diacetylcurcumin

Stoichiometric reactions of 4,4'‐diacetylcurcumin (HL) with series of transition metal ions, namely Fe3+, Co2+, Ni2+ and Zn2+, in methanol result in the corresponding homoleptic metal complexes. All the obtained complexes were characterized by elemental analysis, high resolution mass spectrometry, IR spectroscopy, magnetic moment and single‐crystal X‐ray diffraction. Structural analyses are unprecedentedly performed for the FeIII, CoII, and NiII complexes and reveal octahedral mononuclear complexes with the compositions [Fe(L)3] and [M(L)2(MeOH)2] (M = Co2+, Ni2+, Zn2+) for trivalent and divalent metal ions, respectively. In all complexes, the deprotonated ligands serve as monoanionic and bidentate ligands with (O,O)‐chelating β‐diketonate moieties. The free ligand HL exhibits considerable antiproliferative effects for the human MCF‐7 breast and HepG2 liver cancer cells with IC50 values of 20.91 ± 2.16 μg·mL–1 and 12.85 ± 1.85 μg·mL–1, respectively. The CoII and ZnII complexes with IC50 values in the range of 14.53–20.80 μg·mL–1 for MCF‐7 breast and 8.48–10.68 μg·mL–1 for HepG2 liver cancer cells show stronger antiproliferative effects than HL, the FeIII and NiII complexes cause weaker reductions of the growth of the two tested cancer cell lines.

Phosphine ligands as protecting groups for 3d complexes in oxidation by O2

A series of heteroleptic mixed phosphine/alkoxide 3d complexes was designed to evaluate PPh3 as a protecting group, stabilizing the metal coordination sphere prior to O2 exposure, but oxidatively dissociating in the presence of O2 to allow facile O2 reduction by low coordinate metal centers. Complexes of the form [(Ph3P)2M(OC4F9)2] (M = Fe (1), Co (2), Ni (3), Zn (4)) and [(Ph3P)2M(pinF)] (M = Co (8), Ni (9), Zn (10) were prepared, along with related complexes with non-reactive l-donors, [(DME)Fe(OC4F9)2] (5) and [(Ph3PO)2M(OC4F9)2] (M = Fe (6), Ni (7)). Complexes were characterized by UV–vis and NMR spectroscopies, elemental analysis, and single-crystal X-ray diffraction for 1, 3, 6, 7, 8, 9, and 10. The electronic structure of 3 is particularly notable, with ~D4h geometry at room temperature and ~Td at low temperature, as determined by temperature dependent UV–vis and NMR (1H, 31P) spectroscopies. Complexes (M = Fe, Co, Ni) were screened for O2 reactivity to assess the efficacy of PPh3 as a protecting group. Dimeric [Fe2(μ2-O)(OPPh3)2(OC4F9)4] (13) was isolated after O2 reactivity with 1 and characterized as described above. Related Fe complexes 5 and 6 were each combined with O2 to generate intermediate species capable of both stoichiometric oxidase of hydroquinone to benzoquinone and sub-stoichiometric oxygen atom transfer of thioanisole (PhSMe) to methyl phenyl sulfoxide. Fluorinated alkoxide ligand choice influenced O2 reactivity in CoII complexes, as reactivity was only seen in the less sterically hindering pinF–containing complex 8. In the NiII complexes, on the other hand, the particular fluorinated ligand was not a factor in O2 reduction, as 3 and 9 exhibited similar reactivity. Related dimeric compounds [Co2(pinF)2(THF)4)] (11) and [Zn2(pinF)2(THF)2)] (12) were also isolated and characterized.

CoII Complexes as Liposomal CEST Agents.

Three paramagnetic CoII macrocyclic complexes containing 2-hydroxypropyl pendant groups, 1,1',1'',1'''-(1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl)tetrakis- (propan-2-ol) ([Co(L1)]2+ , 1,1'-(4,11-dibenzyl-1,4,8,11-tetraazacyclotetradecane-1,8-diyl)bis(propan-2-ol) ([Co(L2)]2+ ), and 1,1'-(4,11-dibenzyl-1,4,8,11-tetraazacyclotetradecane-1,8-diyl)bis(octadecan-2-ol) ([Co(L3)]2+ ) were synthesized to prepare transition metal liposomal chemical exchange saturation transfer (lipoCEST) agents. In solution, ([Co(L1)]2+ ) forms two isomers as shown by 1 H NMR spectroscopy. X-ray crystallographic studies show one isomer with 1,8-pendants in cis-configuration and a second isomer with 1,4-pendants in trans-configuration. The [Co(L2)]2+ complex has 1,8-pendants in a cis-configuration. Remarkably, the paramagnetic-induced shift of water 1 H NMR resonances in the presence of the [Co(L1)]2+ complex is as large as that observed for one of the most effective LnIII water proton shift agents. Incorporation of [Co(L1)]2+ into the liposome aqueous core, followed by dialysis against a solution of 300 mOsm L-1 produces a CEST peak at 3.5 ppm. Incorporation of the amphiphilic [Co(L3)]2+ complex into the liposome bilayer produces a more highly shifted CEST peak at -13 ppm. Taken together, these data demonstrate the feasibility of preparing CoII lipoCEST agents.

Molybdenum(III) Thiocyanate- and Selenocyanate-Based One-Dimensional Heteronuclear Polymers: Coordination Affinity-Controlled Assemblage of Mixed Spin and Mixed Valence Derivatives with Ni(II) and Co(II/III).

One-dimensional coordination polymers constructed with the 4d metallo-ligand [Mo(NCS)6]3- associated with NiII and CoII complexes are reported. The first series consists of anionic NCS-bridged [Mo-MII]- coordination polymers associated with a discrete paramagnetic complex or a diamagnetic CoIII complex acting as cations. The latter takes advantage of the coordination preference of the S-ligand for the soft 3d ions and has led to hetero-trimetallic [MoIIINiIICoIII] and mixed valence [MoIIICoIICoIII] compounds. A second series concerns neutral chains in which trinuclear [Mo M2II] units are bridged by an additional NCS anion. The soft character of the S atom was also the key to a rare example of a compound involving both high-spin and low-spin CoII centers associated with [Mo(NCS)6]. A [Mo-Ni] derivative obtained with [Mo(NCSe)6]3- has been considered in order to evaluate the effect of Se versus S on the exchange interaction. The spin distribution for selenocyanate metallo-ligand has been assessed by density functional theory calculations. The crystal structures for all compounds have been characterized, and their magnetic behaviors have been investigated. These ferrimagnetic systems are characterized by antiferromagnetic Mo-MII interactions in the range of -40 to -90 cm-1 (based on H = -JSaSb formalism) operative both with CoII and with NiII, thus demonstrating the potential of the MoIII-NCS combination for molecular systems in which exchange interactions play an important role.

Structurally characterized dinuclear zinc(II) and copper(II) coumarin-based N2O2-donor complexes: syntheses, Hirshfeld analyses and fluorescent properties

Two newly designed dinuclear ZnII and CoII complexes [Co2(L)2]·H2O (1) and [Zn2(L)2]·H2O (2) of a coumarin-based N2O2-donor ligand H2L (5′-(N,N′-diethylamino)-6′-methyl-2,2′-[ethylenedioxybis(nitrilomethylidyne)]phenolcoumarinphenol) were synthesized and characterized by physicochemical and spectroscopic methods. Complexes 1 and 2 are extremely rare asymmetric binuclear structures. The structures of complexes 1 and 2 are isostructural. In both complexes, one metal atom (Co2 or Zn1) adopts a twisted square pyramid configuration, while another metal atom (Co1 or Zn2) adopts a twisted triangular bipyramid configuration with penta-coordination. In addition, complexes 1 and 2 form 3D supramolecular structures through intermolecular hydrogen bonding interactions. Furthermore, the Hirshfeld surfaces analyses and fluorescence properties of complexes 1 and 2 have been discussed in detail.

Tuning Magnetic Anisotropy in a Class of Co(II) Bis(hexafluoroacetylacetonate) Complexes.

Tuning the magnetic anisotropy of metal ions remains highly interesting in the design of improved single-molecule magnets (SMMs). We herein report synthetic, structural, magnetic, and computational studies of four mononuclear CoII complexes, namely [Co(hfac)2 (MeCN)2 ] (1), [Co(hfac)2 (Spy)2 ] (2), [Co(hfac)2 (MBIm)2 ] (3), and [Co(hfac)2 (DMF)2 ] (4) (MeCN=acetonitrile, hfac=hexafluoroacetylacetone, Spy=4-styrylpyridine, MbIm=5,6-dimethylbenzimidazole, DMF=N,N-dimethylformamide), with distorted octahedral geometry constructed from hexafluoroacetylacetone (hfac) and various axial ligands. By a building block approach, complexes 2-4 were synthesized by recrystallization of the starting material of 1 from various ligands containing solution. Magnetic and theoretical studies reveal that 1-4 possess large positive D values and relative small E parameters, indicating easy-plane magnetic anisotropy with significant rhombic anisotropy in 1-4. Dynamic alternative current (ac) magnetic susceptibility measurements indicate that these complexes exhibit slow magnetic relaxation under external fields, suggesting field-induced single-ion magnets (SIMs) of 1-4. These results provide a promising platform to achieve fine tuning of magnetic anisotropy through varying the axial ligands based on Co(II) bis(hexafluoroacetylacetonate) complexes.

Homoleptic Mononuclear Tris‐Chelate Complexes of FeII, CoII, NiII, and ZnII Based on a Redox‐Active Imidazolyl‐2‐thione Ligand: Structural and Electrochemical Correlation

Five mononuclear tris‐chelate complexes of FeII, CoII, NiII and ZnII, containing the bidentate ligand 3‐methyl‐1‐(2‐pyridyl)imidazolyl‐2‐thione (L), have been synthesised and characterised, namely [MII(L)3](BF4)2, where M = Fe (1), Co (2), Ni (3) and Zn (4), and [FeII(L)3](PF6)2 {1‐(PF6)2}. The complexes have been characterised by standard methods and single‐crystal X‐ray diffraction, showing that all the complexes are isostructural and isomorphs, crystallising in the P1 space group, except for 1‐(PF6)2, which crystallises in the P21/c, as expected due to the different size and symmetry of the anion. The metal centre is found in a distorted meridional‐N3S3 octahedral geometry. In all the complexes, two ligand strands within the same complex cation unit interact via an almost perfect face‐to‐face π–π stacking. The double intramolecular interaction occurs between a pyridyl ring of one ligand strand and an imidazolyl ring of a second ligand strand and vice versa. The FeII and CoII complexes, 1 and 2, are stabilised in the high spin state, based on the bond lengths and angles obtained by SC‐XRD and by VT‐magnetic studies in the solid state and NMR Evans method in CD3CN solution. The cyclic voltammetry behaviour for compounds 1–4 showed an EC mechanism for the oxidation process, in which two ligand strands are electrochemically oxidised, instead of the metal centre, followed by a chemical process (de‐coordination and dimerisation). Whereas, the reduction process involved metal electrodeposition for the FeII, NiII and ZnII complexes. In the case of the CoII complex, the voltammetric response suggested a multistep decomposition process during the electrochemical reduction. Finally, a linear correlation between the oxidation potential of the ligand and the average M–N bond length has been found, permitting the modification of the oxidation potential by selection of the metal centre.

Ligand-Based Reactivity of Oxygenation and Alkylation in Cobalt Complexes Binding with (Thiolato)phosphine Derivatives.

In our efforts to understand the nature of metal thiolates, we have explored the chemistry of cobalt ion supported by (thiolato)phosphine ligand derivatives. Herein, we synthesized and characterized a square-planar CoII complex binding with a bidentate (thiolato)phosphine ligand, Co(PS1″)2 (1) ([PS1″]- = [P(Ph)2(C6H3-3-SiMe3-2-S)]-). The complex activates O2 to form a ligand-based oxygenation product, Co(OPS1″)2 (2) ([OPS1″]- = [PO(Ph)2(C6H3-3-SiMe3-2-S)]-). In addition, an octahedral CoIII complex with a tridentate bis(thiolato)phosphine ligand, [NEt4][Co(PS2*)2] (3) ([PS2*]2- = [P(Ph)(C6H3-3-Ph-2-S)2]2-), was obtained. Compound 3 cleaves the C-Cl bond in dichloromethane via an S-based nucleophilic attack to generate a chloromethyl thioether group. Two isomeric products, [Co(PS2*)(PSSCH2Cl*)] (4 and 4') ([PSSCH2Cl*]- = [P(Ph)(C6H3-3-Ph-2-S)(C6H3-3-Ph-2-SCH2Cl)]-), were isolated and fully characterized. Both transformations, oxygenation of a CoII-bound phosphine donor in 1 and alkylation of a CoIII-bound thiolate in 3, were monitored by spectroscopic methods. These reaction products were isolated and fully characterized. Density functional theory (DFT, the B3LYP functional) calculations were performed to understand the electronic structure of 1 as well as the pathway of its transformation to 2.

Electrochemical CO2 and Proton Reduction by a Co(dithiacyclam) Complex

While [Ni(cyclam)]2+ and [Ni(dithiacyclam)]2+ complexes were shown to be potent electrocatalysts for the CO2 conversion, their respective Co complexes hitherto received only little attention. Herein, we report on the CoII complexes of the cyclam and dithiacyclam platform, describe their synthesis and reveal their rich solvent dependent coordination chemistry. We show that sulfur implementation into the cyclam moiety leads to a switch from a low spin CoII complex in [Co(cyclam)]2+ to a high spin form in [Co(dithiacyclam)]2+. Notably, while both complexes are capable to perform the reduction of CO2 to CO, H2 formation is generally preferred. Along this line, the complexes were shown to enable proton reduction from acetic acid. However, in comparison to [Co(cyclam)]2+, the altered electronics make [Co(dithiacyclam)]2+ complexes prone to deposit on the glassy carbon working electrode over time leading to an overall low faradaic efficiency for the reduction of protons or CO2.

Weakly Coordinated Cobaltacycles: Trapping Catalytically Competent Intermediates in Cp*CoIII Catalysis.

Herein, we disclose the synthesis of metallacyclic Cp*CoIII complexes containing weakly chelating functional groups. We have employed these compounds not only as an exceptional platform for accessing some of the most widely invoked transient intermediates in C-H functionalization processes but also as competent catalysts in different Cp*Co-catalyzed transformations, including a benchmark coupling reaction.