Cobalt-Catalyzed Cyclization/Hydrosilylation Reaction of 1,6-Diynes Enabled by an Oxidative Cyclization–Hydrosilylation Mechanism

Transition-metal-catalyzed cyclization/hydrosilylation of 1,6-diynes is a useful method for the preparation of five-membered ring-fused silyl dienes that are useful reagents in organic synthesis. Only a handful of noble metal catalysts facilitating this transformation are known, and nonprecious metal catalysts effecting the reaction have remained elusive. Herein, we report that low-coordinate Co(0)-N-heterocyclic carbene complexes can catalyze the cyclization/hydrosilylation of 1,6-diynes with tertiary and secondary hydrosilanes, furnishing five-membered ring-fused (Z)-1-silyldienes in good yields and excellent stereoselectivity. Mechanistic study disclosed that the catalytic cycle likely has oxidative cyclization of 1,6-diynes with Co(0) species as the key step. This mechanism accounts for the high stereoselectivity and absence of uncyclized hydrosilylation byproducts in the cobalt-catalyzed cyclization/hydrosilylation reaction, which is different from the hydrosilylation-cyclization mechanism of the noble metal-catalyzed reactions

Cobalt-Catalyzed Cyclization/Hydrosilylation Reaction of 1,6-Diynes Enabled by an Oxidative Cyclization–Hydrosilylation Mechanism

Transition-metal-catalyzed cyclization/hydrosilylation of 1,6-diynes is a useful method for the preparation of five-membered ring-fused silyl dienes that are useful reagents in organic synthesis. Only a handful of noble metal catalysts facilitating this transformation are known, and nonprecious metal catalysts effecting the reaction have remained elusive. Herein, we report that low-coordinate Co(0)-N-heterocyclic carbene complexes can catalyze the cyclization/hydrosilylation of 1,6-diynes with tertiary and secondary hydrosilanes, furnishing five-membered ring-fused (Z)-1-silyldienes in good yields and excellent stereoselectivity. Mechanistic study disclosed that the catalytic cycle likely has oxidative cyclization of 1,6-diynes with Co(0) species as the key step. This mechanism accounts for the high stereoselectivity and absence of uncyclized hydrosilylation byproducts in the cobalt-catalyzed cyclization/hydrosilylation reaction, which is different from the hydrosilylation-cyclization mechanism of the noble metal-catalyzed reactions

Zwitterionic Cobalt(I)–NHC Complexes with Tetraphenylborate Ligation: Synthesis, Characterization, and Reactivity

Zwitterionic metal complexes of Rh and Ru featuring a tetraphenylborate ancillary ligand have been explored widely in organometallic chemistry. Analogous 3d metal complexes, however, are rarely known. From the oxidation reaction of cobalt(0)-N-heterocyclic carbene complexes [(NHC)­Co­(η2:η2-(CH2CHSiMe2)2O)] (NHC = N-heterocyclic carbene) with [Cp2Fe]­[BPh4], we synthesized the zwitterionic cobalt­(I)–NHC complexes [(IMes)­Co­((η6-C6H5)­BPh3)] (IMes = 1,3-bis­(2,4,6-trimethylphenyl)-imidazole-2-ylidene, 1) and [(IPr)­Co­((η6-C6H5)­BPh3)] (IPr = 1,3-bis­(2,6-diisopropylphenyl)-imidazole-2-ylidene, 2) in good yields. Characterization data and computational studies revealed the S = 1 ground spin state for 1 and 2. These zwitterionic cobalt­(I) complexes can act as cobalt­(I) synthons to prepare cobalt­(I)–NHC complexes bearing other ancillary ligands. Their reactions to CO and CNBut form the zwitterionic cobalt­(I) complexes [(IMes)­Co­((η6-C6H5)­BPh3)­(CO)] (3), [(IPr)­Co­((η6-C6H5)­BPh3)­(CO)] (4), and [(IMes)­Co­((η6-C6H5)­BPh3)­(CNBut)] (5) and the ionic cobalt­(I) complex [(IMes)­Co­(CNBut)4]­[BPh4] (6). In the reactions of 2 with pyridine, IPr, and IMes, the ionic cobalt­(I)–NHC complexes [(IPr)­Co­(py)3]­[BPh4] (7), [(IPr)2Co]­[BPh4] (8) and [(IPr)­Co­(IMes)]­[BPh4] (9) were formed. The structures of these complexes were established by single-crystal X-ray diffraction studies

Zwitterionic Cobalt(I)–NHC Complexes with Tetraphenylborate Ligation: Synthesis, Characterization, and Reactivity

Zwitterionic metal complexes of Rh and Ru featuring a tetraphenylborate ancillary ligand have been explored widely in organometallic chemistry. Analogous 3d metal complexes, however, are rarely known. From the oxidation reaction of cobalt(0)-N-heterocyclic carbene complexes [(NHC)­Co­(η2:η2-(CH2CHSiMe2)2O)] (NHC = N-heterocyclic carbene) with [Cp2Fe]­[BPh4], we synthesized the zwitterionic cobalt­(I)–NHC complexes [(IMes)­Co­((η6-C6H5)­BPh3)] (IMes = 1,3-bis­(2,4,6-trimethylphenyl)-imidazole-2-ylidene, 1) and [(IPr)­Co­((η6-C6H5)­BPh3)] (IPr = 1,3-bis­(2,6-diisopropylphenyl)-imidazole-2-ylidene, 2) in good yields. Characterization data and computational studies revealed the S = 1 ground spin state for 1 and 2. These zwitterionic cobalt­(I) complexes can act as cobalt­(I) synthons to prepare cobalt­(I)–NHC complexes bearing other ancillary ligands. Their reactions to CO and CNBut form the zwitterionic cobalt­(I) complexes [(IMes)­Co­((η6-C6H5)­BPh3)­(CO)] (3), [(IPr)­Co­((η6-C6H5)­BPh3)­(CO)] (4), and [(IMes)­Co­((η6-C6H5)­BPh3)­(CNBut)] (5) and the ionic cobalt­(I) complex [(IMes)­Co­(CNBut)4]­[BPh4] (6). In the reactions of 2 with pyridine, IPr, and IMes, the ionic cobalt­(I)–NHC complexes [(IPr)­Co­(py)3]­[BPh4] (7), [(IPr)2Co]­[BPh4] (8) and [(IPr)­Co­(IMes)]­[BPh4] (9) were formed. The structures of these complexes were established by single-crystal X-ray diffraction studies

Single-Crystalline Organic–Inorganic Layered Cobalt Hydroxide Nanofibers: Facile Synthesis, Characterization, and Reversible Water-Induced Structural Conversion

New pink organic–inorganic layered cobalt hydroxide nanofibers intercalated with benzoate ions [Co­(OH)­(C₆H₅COO)·H₂O] have been synthesized by using cobalt nitrate and sodium benzoate as reactants in water with no addition of organic solvent or surfactant. The high-purity nanofibers are single-crystalline in nature and very uniform in size with a diameter of about 100 nm and variable lengths over a wide range from 200 μm down to 2 μm by simply adjusting reactant concentrations. The as-synthesized products are well-characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), fast Fourier transforms (FFT), X-ray diffraction (XRD), energy dispersive X-ray spectra (EDX), X-ray photoelectron spectra (XPS), elemental analysis (EA), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and UV–vis diffuse reflectance spectra (UV–vis). Our results demonstrate that the structure consists of octahedral cobalt layers and the benzoate anions, which are arranged in a bilayer due to the π–π stacking of small aromatics. The carboxylate groups of benzoate anions are coordinated to Co^II ions in a strong bridging mode, which is the driving force for the anisotropic growth of nanofibers. When NaOH is added during the synthesis, green irregular shaped platelets are obtained, in which the carboxylate groups of benzoate anions are coordinated to the Co^II ions in a unidentate fashion. Interestingly, the nanofibers exhibit a reversible transformation of the coordination geometry of the Co^II ions between octahedral and pseudotetrahedral with a concomitant color change between pink and blue, which involves the loss and reuptake of unusual weakly coordinated water molecules without destroying the structure. This work offers a facile, cost-effective, and green strategy to rationally design and synthesize functional nanomaterials for future applications in catalysis, magnetism, gas storage or separation, and sensing technology

Production and Characterization of Monoclonal Antibodies against Human Nuclear Protein FAM76B

<div><p>Human FAM76B (hFAM76B) is a 39 kDa protein that contains homopolymeric histidine tracts, a targeting signal for nuclear speckles. FAM76B is highly conserved among different species, suggesting that it may play an important physiological role in normal cellular functions. However, a lack of appropriate tools has hampered study of this potentially important protein. To facilitate research into the biological function(s) of FAM76B, murine monoclonal antibodies (MAbs) against hFAM76B were generated by using purified, prokaryotically expressed hFAM76B protein. Six strains of MAbs specific for hFAM76B were obtained and characterized. The specificity of MAbs was validated by using FAM76B^-/- HEK 293 cell line. Double immunofluorescence followed by laser confocal microscopy confirmed the nuclear speckle localization of hFAM76B, and the specific domains recognized by different MAbs were further elucidated by Western blot. Due to the high conservation of protein sequences between mouse and human FAM76B, MAbs against hFAM76B were shown to react with mouse FAM76B (mFAM76B) specifically. Lastly, FAM76B was found to be expressed in the normal tissues of most human organs, though to different extents. The MAbs produced in this study should provide a useful tool for investigating the biological function(s) of FAM76B.</p></div

Exogenous and endogenous mFAM76B recognized by anti-hFAM76B MAbs.

<p>(A) Intranuclear localization of overexpressed mFAM76B in HEK 293 cells revealed by immunofluorescence staining. HEK 293 cells were transfected with plasmid expressing mFAM76B-Flag and stained with anti-hFAM76B MAbs and anti-Flag MAb. Normal mouse serum was used as a negative control. TRITC-conjugated goat anti-mouse IgG was used as the secondary antibody. Nuclei were labeled with DAPI (blue). (B) Endogenous mFAM76B revealed by immunohistochemical staining with MAbs against hFAM76B. NIH/3T3 and Hepa1-6 cells were fixed with 4% paraformaldehyde and then stained with the anti-hFAM76B MAbs. Normal mouse serum was used as a negative control. Primary Abs were detected by a Vectastain ABC Kit with DAB as a substrate. Nuclei were labeled with hematoxylin. Bar = 50 μm.</p

FAM76B expression in normal human organs.

<p>(A) brain cortex; (B) brain subcortical white matter; (C) liver; (D) spleen; (E) lung; (F) kidney; (G) adrenal gland; (H) heart. All tissues were stained with MAb No.2. FAM76B was found in most organs, though to different extents. The staining was strongest in the nuclei of lymphocytes in the spleen (D), renal tubular epithelium (F), bile duct (C) and glial cells in the brain (A, B). Intermediate staining was observed in the hepatocytes (C), lung (E), and neurons (A). Glomeruli (F) and cardiac muscle (H) were overall minimally stained. Normal mouse serum was used as a negative control. Primary Abs were detected by a Vectastain ABC Kit with DAB as a substrate. Nuclei were labeled with hematoxylin. Bar = 100 μm.</p

Domain mapping for anti-hFAM76B MAbs.

<p>(A) Cartoon of the position of the six different fragments in the FAM76B gene. (B) Western blot analysis of the binding of different anti-hFAM76B MAbs to full-length and six truncated mutants of hFAM76B under denaturing conditions. (C) Map of the domains recognized by different anti-hFAM76B MABs.</p

Western blotting and immunoprecipitation with MAbs against hFAM76B.

<p>(A) All MAbs except for No. 4 recognized hFAM76B-His recombinant protein expressed in <i>E</i>. <i>coli</i>. Truncated CD133-His fusion protein was used as the negative control protein and anti-His MAb was used as the positive control antibody. (B) Recombinant full-length hFAM76B from HEK 293 cells transfected with eukaryotic expressing vector carrying hFAM76B cDNA recognized by anti-FAM76B MAbs. 1and 2 indicated the samples from two independent transfection. (C) Endogenous FAM76B expressed in HepG2 or Shsy5y cells was detected by MAbs against hFAM76B; anti-GAPDH MAb was used as the positive control antibody. (D) Loss of FAM76B expression in FAM76B^-/- HEK 293 cells revealed by MAbs against hFAM76B; anti-GAPDH MAb was used for loading control. (E) The cell lysates of HEK 293 cells overexpressing hFAM76B-Flag were subjected to immunoprecipitation with anti-FAM76B MAbs followed by immunoblotting with anti-Flag MAb. Anti-Flag antibody was used as a positive control and rabbit anti-mouse IgG was used as a negative control.</p