Cobalt Chemistry Research Articles

An Alkaline Flow Battery Based on the Coordination Chemistry of Iron and Cobalt

We present the first alkaline redox flow battery (a-RFB) based on the coordination chemistry of cobalt with 1-[Bis(2-hydroxyethyl)amino]-2-propanol (mTEA) and iron with triethanolamine (TEA) in 5 M NaOH. The overall redox system has a cell voltage of 0.93 V in the charged state. Importantly, the coordination compounds are negatively charged and have limited transport through the cation exchange membrane (e.g., Nafion), minimizing the extent of redox species crossover during charge-discharge cycling. Fe-TEA is electrochemically reversible and soluble up to 0.8 M, whereas Co-mTEA presents quasireversible electron transfer kinetics and can be solubilized up to 0.7 M. Cyclability was tested with a flow cell at a concentration 0.5 M up to 30 cycles using a 50 μm thick Nafion membrane, at 30 mA/cm2, with minimal crossover (less than 4% of net concentration) or evolution of gases detected.

The extended reductive acetyl-CoA pathway: ATPases in metal cluster maturation and reductive activation

The reductive acetyl-coenzyme A (acetyl-CoA) pathway, also known as the Wood-Ljungdahl pathway, allows reduction and condensation of two molecules of carbon dioxide (CO2) to build the acetyl-group of acetyl-CoA. Productive utilization of CO2 relies on a set of oxygen sensitive metalloenzymes exploiting the metal organic chemistry of nickel and cobalt to synthesize acetyl-CoA from activated one-carbon compounds. In addition to the central catalysts, CO dehydrogenase and acetyl-CoA synthase, ATPases are needed in the pathway. This allows the coupling of ATP binding and hydrolysis to electron transfer against a redox potential gradient and metal incorporation to (re)activate one of the central players of the pathway. This review gives an overview about our current knowledge on how these ATPases achieve their tasks of maturation and reductive activation.

A family of polynuclear cobalt complexes upon employment of an indeno-quinoxaline based oxime ligand

The employment of an indeno-quinoxaline based oxime ligand in cobalt chemistry afforded a new family of polynuclear cobalt clusters.

Ligand-Based Carbon–Nitrogen Bond Forming Reactions of Metal Dinitrosyl Complexes with Alkenes and Their Application to C–H Bond Functionalization

Over the past few decades, researchers have made substantial progress in the development of transition metal complexes that activate and functionalize C-H bonds. For the most part, chemists have focused on aliphatic and aromatic C-H bonds and have put less effort into complexes that activate and functionalize vinylic C-H bonds. Our groups have recently developed a novel method to functionalize vinylic C-H bonds that takes advantage of the unique ligand-based reactivity of a rare class of metal dinitrosyl complexes. In this Account, we compare and discuss the chemistry of cobalt and ruthenium dinitrosyl complexes, emphasizing alkene binding, C-H functionalization, and catalysis. Initially discovered in the early 1970s by Brunner and studied more extensively in the 1980s by the Bergman group, the cyclopentadienylcobalt dinitrosyl complex CpCo(NO)2 reacts reversibly with alkenes to give, in many cases, stable and isolable cobalt dinitrosoalkane complexes. More recently, we found that treatment with strong bases, such as lithium hexamethyldisilazide, Verkade's base, and phosphazene bases, deprotonates these complexes and renders them nucleophilic at the carbon α to the nitroso group. This conjugate anion of metal dinitrosoalkanes can participate in conjugate addition to Michael acceptors to form new carbon-carbon bonds. These functionalized cobalt complexes can further react through alkene exchange to furnish the overall vinylic C-H functionalized organic product. This stepwise sequence of alkene binding, functionalization, and retrocycloaddition represents an overall vinylic C-H functionalization reaction of simple alkenes and does not require directing groups. We have also developed an asymmetric variant of this reaction sequence and have used this method to synthesize C1- and C2-symmetric diene ligands with high enantioinduction. Building upon these stepwise reactions, we eventually developed a simple one-pot procedure that uses stoichiometric amounts of a cobalt dinitrosoalkane complex for both inter- and intramolecular C-H functionalization. We can achieve catalysis in one-pot intramolecular reactions with a limited range of substrates. Our groups have also reported an analogous ruthenium dinitrosyl complex. In analogy to the cobalt complex, this ruthenium complex reacts with alkenes in the presence of neutral bidentate ligands, such as TMEDA, to give octahedral dinitrosoalkane complexes. Intramolecular functionalization or cyclization of numerous ruthenium dinitrosoalkane complexes proceeds under mild reaction conditions to give the functionalized organic products in excellent yields. However, despite extensive efforts, so far we have not been able to carry out intermolecular reactions of these complexes with a variety of electrophiles or C-H functionalization reactions. Although additional work is necessary to further boost the catalytic capabilities of both cobalt and ruthenium dinitrosyl complexes for vinylic C-H functionalization of simple alkenes, we believe this ligand-based vinylic C-H functionalization reaction has provided chemists with a useful set of tools for organic synthesis.

Catalytic hydrogenation activity and electronic structure determination of bis(arylimidazol-2-ylidene)pyridine cobalt alkyl and hydride complexes.

The bis(arylimidazol-2-ylidene)pyridine cobalt methyl complex, ((iPr)CNC)CoCH3, was evaluated for the catalytic hydrogenation of alkenes. At 22 °C and 4 atm of H2 pressure, ((iPr)CNC)CoCH3 is an effective precatalyst for the hydrogenation of sterically hindered, unactivated alkenes such as trans-methylstilbene, 1-methyl-1-cyclohexene, and 2,3-dimethyl-2-butene, representing one of the most active cobalt hydrogenation catalysts reported to date. Preparation of the cobalt hydride complex, ((iPr)CNC)CoH, was accomplished by hydrogenation of ((iPr)CNC)CoCH3. Over the course of 3 h at 22 °C, migration of the metal hydride to the 4-position of the pyridine ring yielded (4-H2-(iPr)CNC)CoN2. Similar alkyl migration was observed upon treatment of ((iPr)CNC)CoH with 1,1-diphenylethylene. This reactivity raised the question as to whether this class of chelate is redox-active, engaging in radical chemistry with the cobalt center. A combination of structural, spectroscopic, and computational studies was conducted and provided definitive evidence for bis(arylimidazol-2-ylidene)pyridine radicals in reduced cobalt chemistry. Spin density calculations established that the radicals were localized on the pyridine ring, accounting for the observed reactivity, and suggest that a wide family of pyridine-based pincers may also be redox-active.

The Intricate Chemistry of Cobalt(II) Halides and Bis(diphenylphosphanyl)ethane

Phosphane complexes of the putative formula [CoX2(dppe)] [X = Cl, Br, I; dppe = bis(diphenylphosphanyl)ethane] are frequently used catalyst precursors in cobalt-catalyzed reactions. Despite their widespread use, these complexes have not been structurally characterized. We demonstrate that synthetic procedures for [CoX2(dppe)] afford complexes of the formula [Co4X8(dppe)5] instead. Crystallographic analyses of these complexes reveal an ionic structure with pentacoordinate [CoX(dppe)2]+ cations and a dinuclear [Co2X6(dppe)]2– anion. The bromido and iodido complexes crystallize in two forms, which differ in the geometry of the cation (square-pyramidal vs trigonal-bipyramidal).

Influence of the Metal (Al, Cr, and Co) and Substituents of the Porphyrin in Controlling Reactions Involved in Copolymerization of Propylene Oxide and Carbon Dioxide by Porphyrin Metal(III) Complexes. 3. Cobalt Chemistry

A series of cobalt(III) complexes LCoX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyirn (OEP) and X = Cl or acetate, has been investigated for homopolymerization of propylene oxide (PO) and copolymerization of PO and CO2 to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively. These reactions were carried out both with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN(+)Cl(-) (bis(triphenylphosphine)iminium chloride). The PO/CO2 copolymerization process is notably faster than PO homopolymerization. With ionic PPN(+)Cl(-) cocatalyst the TPPCoOAc catalyst system grows two chains per Co center and the presence of excess [Cl(-)] facilitates formation of PC by two different backbiting mechanisms during copolymerization. Formation of PPC is dependent on both [Cl(-)] and the CO2 pressure employed (1-50 bar). TPPCoCl and PO react to form TPPCo(II) and ClCH2CH(Me)OH, while with DMAP, TPPCoCl yields TPPCo(DMAP)2(+)Cl(-). The reactions and their polymers and other products have been monitored by various methods including react-IR, FT-IR, GPC, ESI, MALDI TOF, EXAFS, and NMR ((1)H, (13)C{(1)H}) spectroscopy. Notable differences are seen in these reactions with previous studies of (porphyrin)M(III) complexes (M = Al, Cr) and of the (salen)M(III) complexes where M = Cr, Co.

Solid state coordination chemistry of cobalt(II) with carboxyphenyltetrazoles

The hydrothermal reaction of the appropriate Co(II) salt and 3- or 4-carboxyphenyltetrazole yielded the molecular [Co(3-trzphCO2H)2(H2O)4] (2) and the three-dimensional phases [Co(3-trzphCO2)] (3), [Co(4-trzphCO2)(H2O)] (4), and [Co(SO4)(OH)(3-trzphCO2H)] (5). The compounds exhibit a range of tetrazolate bonding motifs, including monodentate in 2, bidentate bridging in 3, bridging to three cobalt sites in 4 and bridging four cobalt sites in 5. The three-dimensional connectivities of 3–5 are achieved through the additional linkages provided by the carboxylate groups. The secondary building units include Co-tetrazolate chains in 3, Co-tetrazolate double chains in 4 and {Co3(tetrazolate)3(OH)}2+ trinuclear units in 5.

Chemistry of Cobalt(II) Confined in the Pores of Ordered Silica Monoliths: From the Formation of the Monolith to the CoFe Prussian Blue Analogue Nanocomposite

Recently we conceived of an original strategy that allows the precipitation of Prussian blue analogues (PBAs) in the ordered pores of silica monoliths to lead to photomagnetic CoFe PBA-silica nanocomposites. To determine the critical parameters and fully control the synthesis of the photoactive CoFe PBA in the pores of the silica matrix, X-ray absorption spectroscopy was performed at the cobalt K-edge. This study showed that cobalt cation chemistry is the keystone of the entire process. The local environment and the electronic structure of the cobalt cation undergo several modifications during the formation process: first the incorporation of the cation as an octahedral complex into the ordered block copolymer phase, then the deprotonation by thermohydrolysis to give a fourfold-coordinated deprotonated lowly condensed species and finally the formation of the 3D coordination network of CoFe PBA in acidic conditions through a rapid reprotonation followed by nucleophilic substitution accompanied by the electronic transfer, thus leading to the photomagnetic Co(III)(LS)-Fe(II)(LS) (LS=low spin) pairs.

Extending the coordination chemistry of cobalt with the metalloligand [Pt2(μ-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives

The coordination chemistry of the metalloligand [Pt2(μ-S)2(PPh3)4] towards cobalt(II) and cobalt(III) centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed methodology. Reaction of [Pt2(μ-S)2(PPh3)4] with CoCl2·6H2O in methanol gave a green-yellow suspension of the known adduct [Pt2(μ-S)2(PPh3)4CoCl2], and the CoBr2 adduct could be similarly prepared. When in situ-generated [Pt2(μ-S)2(PPh3)4CoCl2] is reacted with 8-hydroxyquinoline (HQ) and base, the initial product is the cobalt(II) adduct [Pt2(μ-S)2(PPh3)4CoQ]+, which is then converted in air to the cobalt(III) adduct [Pt2(μ-S)2(PPh3)4CoQ2]+, isolated as its hexafluorophosphate salt. The corresponding picolinate (Pic) derivative [Pt2(μ-S)2(PPh3)4Co(Pic)2]+ was similarly prepared, however reaction of [Pt2(μ-S)2(PPh3)4], CoCl2·6H2O and 8-(tosylamino)quinoline (HTQ) produced only the cobalt(II) adduct [Pt2(μ-S)2(PPh3)4CoTQ]+. Reactions of [Pt2(μ-S)2(PPh3)4], CoCl2·6H2O and dithiocarbamates gave cobalt(III) complexes [Pt2(μ-S)2(PPh3)4Co(S2CNR2)2]+ [R=Et or R2=(CH2)4], and proceeded much more rapidly, consistent with the known ability of the dithiocarbamate ligand to stabilize cobalt in higher oxidation states. A study of the fragmentation of cobalt(III) adducts by positive-ion ESI mass spectrometry indicated that [Pt2(μ-S)2(PPh3)4CoQ2]+ fragments to form the radical cation [Pt2(μ-S)2(PPh3)4]+, which could also be generated by ESI MS analysis of [Pt2(μ-S)2(PPh3)4] in methanol–NaOH solution. In contrast, the corresponding indium(III) derivative [Pt2(μ-S)2(PPh3)4InQ2]+, and the cobalt(III) dithiocarbamate [Pt2(μ-S)2(PPh3)4Co(S2CN(CH2)4)2]+ are much more reluctant to fragment under analogous conditions, and the differences are discussed in terms of cobalt(III) redox chemistry.

Bis-tris propane as a new multidentate ligand for nickel- and cobalt-based spin clusters

We describe the first use of Bis-tris propane {2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxymethyl)propane-1,3-diol], H(6)L}, in nickel and cobalt chemistry and report the synthesis, structure and magnetic properties of [Ni(4)(H(4)L)(H(3)L)(acac)(2)](+) (1) and [Co(II)(3)Co(III)(2)(H(2)L)(2)(acac)(3)(MeOH)](+) (2).

Capture and release of alkyne-derivatized glycerophospholipids using cobalt chemistry.

Alkyne modified phospholipids can be unambiguously identified and differentiated from native species in complex mixtures by formation of dicobalthexacarbonyl complexes. This reaction is specific for alkynes and is unaffected by other glycerophospholipid related moieties. Enrichment of cells with alkyne-derivatized fatty acids or glycerophospholipids followed by solid phase sequestration and release is a promising new method for unequivocally monitoring individual glycerophospholipids following incorporation and facilitates lipidomic analysis of substrates and products.

Use of the 2‐Pyridinealdoxime/N,N′‐Donor Ligand Combination in Cobalt(III) Chemistry: Synthesis and Characterization of Two Cationic Mononuclear Cobalt(III) Complexes

The use of 2-pyridinealdoxime (paoH)/N,N′-donor ligand (L-L) “blend” in cobalt chemistry has afforded two cationic mononuclear cobalt(III) complexes of the general type [Co(pao)2(L-L)]+, where L-L = 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy). The CoCl2/paoH/L-L (1 : 2 : 1) reaction system in MeOH gives complexes [CoIII(pao)2(phen)]Cl·2H2O (1·2H2O) and [CoIII(pao)2(bpy)]Cl·1.5MeOH (2·1.5MeOH). The structures of the complexes were determined by single-crystal X-ray crystallography. The CoIII ions are six-coordinate, surrounded by three bidentate chelating ligands, that is, two pao− and one phen or bpy. The deprotonated oxygen atom of the pao− ligand remains uncoordinated and participates in hydrogen bonding with the solvate molecules. IR data of the complexes are discussed in terms of the nature of bonding and the known structures.

Organização supramolecular da ftalocianina de cobalto(II) e seu efeito na oxidação do aminoácido cisteína

The interest in the chemistry of cobalt (II) tetrasulfonated phthalocyanine (PcTsCo) comes mainly from its macrocycle-ligand structure combined with their special chemical characteristics, such as high solubility, well-defined redox reactions and remarkable optical absorption in the visible region. In this work, we use layer-by-layer technique in order to assemble CoTsPc and poly(allylaminehydrochloride) (PAH) in hybrid supramolecular system. The electronic spectroscopy and cyclic voltammetry techniques were utilized to study PAH/CoTsPc multilayers growth and the cysteine catalytic oxidation. PAH/CoTsPc showed high electrochemical stability and worthwhile to mention is the remarkable influence of supramolecular arrangement on the final redox properties of the system.

Conductance of a Cobalt(II) Terpyridine Complex Based Molecular Transistor: A Computational Analysis

A recent experiment, in which a molecular transistor based on the coordination chemistry of cobalt(II) and organic self-assembled monolayers is formed by means of self-aligned lithography,2 is analyzed with a computational approach. The calculations reveal that a complex involving two cobalt(II) ions bridged by acetate ions can effectively span the nanogap. This bridged complex is shown to be both more flexible and more conductive than the alternative structure involving a single cobalt(II) ion. The single cobalt(II) ion complex is the more stable structure in a nonconfined environment (i.e., in solution) but is found to be less effective at connecting the leads of the fabricated gap and is less likely to result in a conductive device.

Bioreductive activation and drug chaperoning in cobalt pharmaceuticals

The potential for cobalt(III) complexes in medicine, as chaperones of bioactive ligands, and to target tumours through bioreductive activation, has been examined over the past 20 years. Despite this, chemical properties such as reduction potential and carrier ligands required for optimal tumour targeting and drug delivery have not been optimised. Here we review the chemistry of cobalt(III) drug design, and recent developments in the understanding of the cellular fate of these drugs.

Synthesis of comparable Co-MCM-48 and Co-MCM-41 materials containing high cobalt contents

By a new procedure, Co-MCM-48 and Co-MCM-41 samples have been synthesized with up to 2.5 wt% Co incorporated into the framework. The charge density matching process has been found to be dependent upon the pH in the gel, due to the different solubility of different silica species. By controlling this silica chemistry and also the interfacial chemistry of cobalt during incorporation, the obtained structure and cobalt content of the synthesized materials may be simultaneously controlled. Sodium silicate has been used as the silicon source, which allows for variable amounts of ethanol to be added to the gel, thereby controlling the surfactant packing parameter. Following this approach, Co-MCM-41 and Co-MCM-48 samples with high cobalt contents have been prepared from similar synthesis gels. Due to the similar synthesis conditions, the surface properties of these samples are similar, which may make them well-suited for application as comparable materials in catalysis or adsorption model studies.

The effects of calcium phosphate deposition upon corrosion of CoCr alloys and the potential for implant failure

Physical wear of orthopedic implants is inevitable. CoCr metal samples, typically used in joint reconstruction, corrode rapidly after removal of the protective oxide layer. The behavior of CoCr pellets immersed in human serum, fetal bovine serum (FBS), synovial fluid, and water were studied using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The differences in the corrosive nature of human serum, FBS, synovial fluid, and water after 5 days immersion were highlighted by the oxide/hydroxide layer, which was, respectively, 25, 10, 1.5, and 3-3.5 nm thick. The thickness of calcium phosphate deposit from human serum, FBS, and synovial fluid was, respectively, 30, 20, and 2 nm. Co and Cr ions migrated from the bulk metal surface and were trapped in the serum deposits, where chromium existed as oxides, hydroxides, and phosphates, whereas the cobalt chemistry was dominated only by phosphates and hydroxides. This may account for the composition of wear debris from CoCr orthopedic implants, which are predominantly hydroxyphosphate compounds. From the literature, proteoglycans, pyrophosphates, phospholipids, lubricin, and superficial zone protein (SZP) have been identified as possible causes for the insignificant deposit of calcium phosphate from synovial fluid. Circulation of these compounds around the whole implant may inhibit calcium phosphate deposition and therefore contribute to osteolysis.

Interfacial chemistry of cobalt(II) during sol–gel synthesis of cobalt-containing mesoporous materials

Co-MCM-41 and Co-MCM-48 with cobalt amounts from about 3 wt.% to 9 wt.% have been synthesized under various conditions, and the samples were characterized by XRF, XRD and N 2-sorption. EXAFS least-squares curve fitting detected only oxygen and silicon backscattering shells, which verified the incorporation of cobalt into the silica framework both for as-synthesized and calcined samples. XANES profiles showed that the oxidation state of cobalt in the samples is unaltered during synthesis. It has been shown that the cobalt is precipitated as cobalt hydroxide during synthesis, and this hydroxide is in equilibrium with aqueous cobalt ions in the synthesis gel. The precipitated cobalt hydroxide precursors are incorporated into the mesoporous silica framework, while the aqueous cobalt ions remain dissolved in the aqueous phase. The cobalt amount in the final samples is therefore pH dependent. This equilibrium is also important in the formation of the mesoporous structure. Addition of increasing amounts of cobalt salt to a MCM-48 synthesis gel causes a change in the mesoporous structure from cubic Ia3d to hexagonal, which is suggested to be a consequence of the charge density matching process. The increased amounts of the divalent cobalt(II) ions in the gel screen the negatively charged silica precursors, which decreases the total surface charge density of the silica, and thus causes the surfactants to self-assemble into the hexagonal structure.

Cobalt chemistry with mixed aminotroponiminate salicylaldiminate ligands: synthesis, characterization, and nitric oxide reactivity.

A new class of mixed aminotroponimine salicylaldimine ligands and their corresponding cobalt(II) complexes are reported. This work expands the family of cobalt(II) aminotroponiminato complexes to include salicylaldiminate and derivatized fluorescein moieties. The H2iPrSATI-n (n = 3, 4) ligands 3 and 4, respectively, contain an aminotroponimine moiety and a salicylaldimine fragment connected with an alkyl linker. In the H2iPrFATI-n (n = 3, 4) ligands 5 and 6, a derivatized fluorescein replaces the salicylaldimine fragment. The cobalt(II) complexes [Co(iPrSATI-3)] (7) and [Co2(iPrSATI-4)(2)] (9) were prepared and structurally characterized. The reaction of NO with both complexes ultimately results in the formation of a dinitrogen-containing species. The mononitrosyl, [Co(iPrSATI-3)(NO)] (8), was isolated and characterized. The reactivity of [Co(iPrFATI-3)] (10) and [Co(iPrFATI-4)] (11) with NO mimics that observed for the salicylaldimine derivatives, as monitored by solution IR spectroscopy. When followed by fluorescence spectroscopy, reaction of 11 with NO evoked a 3-fold increase in emission intensity after 22 h.