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1. Cationic cobalt(I) intermediates in hydrofunctionalization reactions

   Parsutkar, Mahesh; Jing, Stanley; Duvvuri, Krishnaja.; RajanBabu, T. V. (April 2020, Book of Abstracts, 259th ACS National Meeting, Philadelphia, PA, March 22-26 2020.)

   Discovery of base metal-catalyzed methods for the preparation of chiral intermediates has garnered great attention. Recently, through a systematic study of activators and ligands, we have discovered Co(I)-catalyzed enantioselective heterodimerization of linear 1,3-dienes with ethylene and acrylates. In these studies, cationic cobalt(I) has been invoked as an active catalyst to carry out the transformation. However, the synthesis and isolation of such active Co(I)-complexes which could give insight into of reaction’s mechanism, remains challenging. Herein, we disclosed a reliable procedure for the synthesis and isolation of Co(I)-complexes and characterized them by UV-Vis spectroscopy and X-ray crystallography. The bis-phosphine ligated Co(I) complexes in presence of activators, performed the regio- and enantioselective hydroboration of 2- substituted 1,3-diene with pinacolborane (HBPin) to obtain homoallylic boronates (enantiomeric excess, ee >90%). In the absence of activators, these complexes do not catalyze the reaction suggesting the key role of cationic Co(I)-species in the catalytic cycle. Currently, these Co(I) complexes are being further utilized in the hydroacylation of 1,3-dienes with simple aliphatic aldehyde to produce enantiopure ketones. The comprehensive protocols for the synthesis of Co(I) complexes and its application in hydrovinylation, heterodimerization with acrylates, hydroboration, and hydroacylation of 1,3-dienes will be discussed. 

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2. Heteroleptic Square Planar Cobalt(I/II) Complexes

   https://doi.org/10.1002/ejic.202200675  

   Gao, Yafei; Lee, Wei‐Tsung; Carta, Veronica; Chen, Chun‐Hsing; Telser, Joshua; Smith, Jeremy_M (January 2023, European Journal of Inorganic Chemistry)

   Abstract Reduction of the cobalt(II) chloride complex, Ph₂B(^tBuIm)₂Co(THF)Cl (1) in the presence of^tBuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph₂B(^tBuIm)₂Co(C≡N^tBu)₂(2). This is a rare example of a 16‐electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of2, as calculated by DFT, reveals that the HOMO is largely d_z²in character. Complex2is readily oxidized to its cobalt(II) congener [Ph₂B(^tBuIm)₂Co(C=N^tBu)₂]BPh₄(3‐BPh₄), whose EPR spectral parameters are characteristic of low‐spin d⁷with an unpaired electron in an orbital of d_z²parentage. This is also consistent with the results of DFT calculations. Despite its 16‐electron configuration and the d_z²parentage of the HOMO, the only tractable reactions of2involve one electron oxidation to afford3. 

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3. Minimal cobalt metabolism in the marine cyanobacterium Prochlorococcus

   https://doi.org/10.1073/pnas.2001393117  

   Hawco, Nicholas J.; McIlvin, Matthew M.; Bundy, Randelle M.; Tagliabue, Alessandro; Goepfert, Tyler J.; Moran, Dawn M.; Valentin-Alvarado, Luis; DiTullio, Giacomo R.; Saito, Mak A. (June 2020, Proceedings of the National Academy of Sciences)

   Despite very low concentrations of cobalt in marine waters, cyanobacteria in the genus Prochlorococcus retain the genetic machinery for the synthesis and use of cobalt-bearing cofactors (cobalamins) in their genomes. We explore cobalt metabolism in a Prochlorococcus isolate from the equatorial Pacific Ocean (strain MIT9215) through a series of growth experiments under iron- and cobalt-limiting conditions. Metal uptake rates, quantitative proteomic measurements of cobalamin-dependent enzymes, and theoretical calculations all indicate that Prochlorococcus MIT9215 can sustain growth with less than 50 cobalt atoms per cell, ∼100-fold lower than minimum iron requirements for these cells (∼5,100 atoms per cell). Quantitative descriptions of Prochlorococcus cobalt limitation are used to interpret the cobalt distribution in the equatorial Pacific Ocean, where surface concentrations are among the lowest measured globally but Prochlorococcus biomass is high. A low minimum cobalt quota ensures that other nutrients, notably iron, will be exhausted before cobalt can be fully depleted, helping to explain the persistence of cobalt-dependent metabolism in marine cyanobacteria. 

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4. Electrocatalytic reduction of nitrate by in situ generated cobalt nanoparticles

   https://doi.org/10.1039/D2CC00853J  

   Ghosh, Moumita; Ibrar, Maha; Smith, Jeremy M. (March 2022, Chemical Communications)

   The cobalt pyridinophane complex [Co( H N4)Cl 2 ] + ( H N4 = 3,7-diaza-1,5(2,6)-dipyridinacyclooctaphane) is converted under catalytic conditions to an electrode-adsorbed species. Aqueous Co 2+ solutions similarly deposit a species under these conditions. Surface characterization reveals the formation of Co nanoparticles. These nanoparticles are active in the electrocatalytic redution of aqueous nitrate. 

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5. Molecular Determinants of Efficient Cobalt-Substituted Hemoprotein Production in E. coli

   https://doi.org/10.1021/acssynbio.3c00481  

   Weaver, Brian R.; Perkins, Lydia J.; Fernandez Candelaria, Froylan Omar; Burstyn, Judith N.; Buller, Andrew R. (November 2023, ACS Synthetic Biology)

   Exchanging the native iron of heme for other metals yields artificial metalloproteins with new properties for spectroscopic studies and biocatalysis. Recently, we reported a method for the biosynthesis and incorporation of a non-natural metallocofactor, cobalt protoporphyrin IX (CoPPIX), into hemoproteins using the common laboratory strain Escherichia coli BL21(DE3). This discovery inspired us to explore the determinants of metal specificity for metallocofactor biosynthesis in E. coli. Herein, we report detailed kinetic analysis of the ferrochelatase responsible for metal insertion, EcHemH (E. coli ferrochelatase). This enzyme exhibits a small, less than 2-fold preference for Fe2+ over the non-native Co2+ substrate in vitro. To test how mutations impact EcHemH, we used a surrogate metal specificity screen to identify variants with altered metal insertion preferences. This engineering process led to a variant with an ∼30-fold shift in specificity toward Co2+. When assayed in vivo, however, the impact of this mutation is small compared to the effects of alteration of the external metal concentrations. These data suggest that incorporation of cobalt into PPIX is enabled by the native promiscuity of EcHemH coupled with BL21’s impaired ability to maintain transition-metal homeostasis. With this knowledge, we generated a method for CoPPIX production in rich media, which yields cobalt-substituted hemoproteins with >95% cofactor purity and yields comparable to standard expression protocols for the analogous native hemoproteins. 

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