Catalytic Synthesis of 8‐Membered Ring Compounds via Cobalt(III)‐Carbene Radicals

The metalloradical activation of o‐aryl aldehydes with tosylhydrazide and a cobalt(II) porphyrin catalyst produces cobalt(III)‐carbene radical intermediates, providing a new and powerful strategy for the synthesis of medium‐sized ring structures. Herein we make use of the intrinsic radical‐type reactivity of cobalt(III)‐carbene radical intermediates in the [Co^II(TPP)]‐catalyzed (TPP=tetraphenylporphyrin) synthesis of two types of 8‐membered ring compounds; novel dibenzocyclooctenes and unprecedented monobenzocyclooctadienes. The method was successfully applied to afford a variety of 8‐membered ring compounds in good yields and with excellent substituent tolerance. Density functional theory (DFT) calculations and experimental results suggest that the reactions proceed via hydrogen atom transfer from the bis‐allylic/benzallylic C?H bond to the carbene radical, followed by two divergent processes for ring‐closure to the two different types of 8‐membered ring products. While the dibenzocyclooctenes are most likely formed by dissociation of o‐quinodimethanes (o‐QDMs) which undergo a non‐catalyzed 8π‐cyclization, DFT calculations suggest that ring‐closure to the monobenzocyclooctadienes involves a radical‐rebound step in the coordination sphere of cobalt. The latter mechanism implies that unprecedented enantioselective ring‐closure reactions to chiral monobenzocyclooctadienes should be possible, as was confirmed for reactions mediated by a chiral cobalt‐porphyrin catalyst.     

Catalytic Dibenzocyclooctene Synthesis via Cobalt(III)–Carbene Radical and ortho‐Quinodimethane Intermediates

The metalloradical activation of ortho‐benzallylaryl N‐tosyl hydrazones with [Co(TPP)] (TPP=tetraphenylporphyrin) as the catalyst enabled the controlled exploitation of the single‐electron reactivity of the redox non‐innocent carbene intermediate. This method offers a novel route to prepare eight‐membered rings, using base metal catalysis to construct a series of unique dibenzocyclooctenes through selective C_carbene?C_aryl cyclization. The desired eight‐membered‐ring products were obtained in good to excellent yields. A large variety of aromatic substituents are tolerated. The proposed reaction mechanism involves intramolecular hydrogen atom transfer (HAT) to Co^III–carbene radical intermediates followed by dissociation of an ortho‐quinodimethane that undergoes 8π cyclization. The mechanism is supported by DFT calculations, and the presence of radical‐type intermediates was confirmed by trapping experiments.     

新型含七元醚环的脯氨酸衍生物的合成

以L-谷氨酸和苯甲醛为起始原料,经7步反应合成了重要中间体(2S,5R)-1-苄基-5-(2-羟乙基)吡咯烷-2-羧酸叔丁酯(1),总产率19%;1经TBDMSCl保护羟基后,用10%Pd/C催化氢解去除苄基制得游离胺(2S,5R)-5-(2-二甲基叔丁基硅氧烷基乙基)吡咯烷-2-羧酸叔丁酯(3);3与Boc-β-Cl-ala,在碱性条件下偶合得氯代烃消去产物(2S,5R)-1-[(2-叔丁氧甲酰胺基)丙烯酰基]-5-(2-二甲基叔丁基硅氧烷基乙基)吡咯烷-2-羧酸叔丁酯(4),或在中性条件下偶合得(2S,5R)-1-[(R)-2-叔丁氧甲酰胺基-3-氯丙酰基]-5-(2-二甲基叔丁基硅氧烷基乙基)吡咯烷-2-羧酸叔丁酯(5);4或5经四丁基氟化铵去除TBDMS保护并发生关环反应合成了新型的七元醚环化合物(4R,7S,9R)-4-甲基-4-叔丁氧甲酰胺基-5-羰基-3-氧杂氮杂卓[1,4]并吡咯[1,2-d]-7-羧基叔丁酯(简称6);6于室温在氯仿中静置2 d~3 d自发转换为其构象异构体(4S,7S,9R)-6(简称6’,6/6’=1/9),其结构经1H NMR,13C NMR,2D NMR和HR-ESI-MS表征。     

Crystal Structure of frans-Dichloro(c-Meso-3,5,7,7,10,12,14,14-Octamethyl-1,4,8,11 -Tetraaza Cyclotetradeca-4,11-Diene)Cobalt(lll) Perchlorate

The crystal structure of the title compound has been solved by X-ray diffraction. [CO(Cl)₂(N₄C₁₈H₃₆)]-(ClO₄), M_r = 537.79, triclinic, P1, a = 6.974(4), b = 8.530(1), c = 11.061(2) Å, α = 98.47(1), β = 106.56(3), γ = 93.02(3)°, V = 620.8(4) ų, Z = 1, Dx = 1.439 Mg m^?3, λ(MoKα) = 0.7093 Å, μ = 0.96 mm^?1, F(000) = 291.93, T = 297(3) K, R = 0.072, R_w = 0.085 for 2121 observed reflections. The Co(III) is six-coordinate with the four N atoms of the macrocyclic ligand equatorial and two Cl ions axial, thereby resulting in a tetragonally distorted octahedral geometry. Aside from the perchlorate group, there exists a non-crystallographic inversion center at the Co(III) ion for the macrocyclic ligand and the two Cl ions which are bonded to the Co(III) ion.     

Synthesis and Oxidative Stability of an Anionic Perfluoroethyl Cobalt(III) Complex

Upon reaction of the versatile tris(perfluoroethyl) cobalt(III) precursor [fac-(MeCN)₃Co(C₂F₅)₃] with potassium tris(pyrazolyl)borate (KTp) in the presence of a tetraphenylphosphonium salt, κ²- and κ³- adducts of the scorpionate ligand with cobalt were observed. Heating this mixture to 50 °C induced complete κ³-coordination of the Tp ligand to cobalt to afford the anionic complex [PPh₄][(κ³-Tp)Co(C₂F₅)₃] in 81 % yield. This new fluoroalkyl cobalt complex was characterized by NMR and UV-Vis spectroscopies, X-ray crystallography, and cyclic voltammetry. The oxidation of [PPh₄][(κ³-Tp)Co(C₂F₅)₃] occurs at much less-positive potentials relative to the related [(MeCN)₃Co(C₂F₅)₃] and [(tpy)Co(C₂F₅)₃] derivatives.     

Sulfitoamine Complexes of Cobalt(III)

Abstract

Monosulfito and bis(hydrogensulfito) cobalt(III) complexes were prepared using sodium sulfite and sodium metabisulfite salts respectively. The two types of products showed different and characterizing patterns of IR and UV-visible spectra. They both contain Co-SO₃ linkages and the sulfite groups have similar or different site symmetries in the same compound.     

Cobalt(III)‐Catalyzed Aryl and Alkenyl CH Aminocarbonylation with Isocyanates and Acyl Azides

Expedient C? H aminocarbonylations of unactivated (hetero)arenes and alkenes were accomplished with a cobalt(III) catalyst that shows high functional group tolerance. The C? H functionalization occurred with excellent chemo‐, site‐, and diastereoselectivity and enabled step‐economical reactions with isocyanates or acyl azides.     

Cobalt(III)‐Catalyzed CH/NO Functionalizations: Isohypsic Access to Isoquinolines

C?H/N?O functionalizations by cobalt(III) catalysis allowed the expedient synthesis of a broad range of isoquinolines. Thus, internal and challenging terminal alkynes proved to be viable substrates for an isohypsic annulation, which was shown to proceed by a facile C?H cobaltation.     

A Two‐Coordinate Cobalt(II) Imido Complex with NHC Ligation: Synthesis,Structure, and Reactivity

The synthesis, structural characterization, and reactivity of the first two‐coordinate cobalt complex featuring a metal–element multiple bond [(IPr)Co(NDmp)] ( 4 ; IPr=1,3‐bis(2′,6′‐diisopropylphenyl)imidazole‐2‐ylidene; Dmp=2,6‐dimesitylphenyl) is reported. Complex 4 was prepared from the reaction of [(IPr)Co(η²‐vtms)₂] (vtms=vinyltrimethylsilane) with DmpN₃. An X‐ray diffraction study revealed its linear C? Co? N core and a short Co? N distance (1.691(6) Å). Spectroscopic characterization and calculation studies indicated the high‐spin nature of 4 and the multiple‐bond character of the Co? N bond. Complex 4 effected group‐transfer reactions to CO and ethylene to form isocyanide and imine, respectively. It also facilitated E? H (E=C, Si) σ‐bond activation of terminal alkyne and hydrosilanes to produce the corresponding cobalt(II) alkynyl and cobalt(II) hydride complexes as 1,2‐addition products.     

冠醚化对双Schiff碱钴（Ⅱ）配合物催化氧化性能的影响

合成了冠醚化钴（Ⅱ）Ｓｃｈｉｆ碱配合物１ｃ及其相关类似物１ｂ，测定了它们的氧加合常数，考查了它们对异丙苯的催化氧化性能，并与未冠醚化的类似物１ａ作比较，讨论了１ｃ分子中的冠环对催化氧化性能的影响     

A Novel Cobalt(III) Mixed-polypyridyl Complex: Synthesis, Characterization and DNA Binding

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｔｒａｎｓｉｔｉｏｎｍｅｔａｌｐｏｌｙｐｙｒｉｄｙｌｃｏｏｒｄｉｎａｔｉｏｎｃｏｍ ｐｏｕｎｄｓａｓｔｈｅｐｒｏｂｅｏｆＤＮＡｓｔｒｕｃｔｕｒｅａｎｄｃｏｎｆｉｇｕｒａｔｉｏｎｈａｖｅｂｅｅｎｅｘｔｅｎｓｉｖｅｌｙｓｔｕｄｉｅｄｉｎｔｈｅｐａｓｔｆｅｗｙｅａｒｓ .ＴｈｅｙｉｎｔｅｒａｃｔｅｆｆｅｃｔｉｖｅｌｙｗｉｔｈＤＮＡｂｙｃｈａｎｇｉｎｇｔｈｅｔｙｐｅｏｆｈｅｔ ｅｒｏａｒｏｍａｔｉｃｌｉｇａｎｄｏｒｍｅｔａｌｃｅｎｔｅｒ.Ｔｈｏｓｅｗｉｔｈｐｈｅｎ(ｐｈｅｎａｎｅ…     

Cluster and Molecular Mechanical Analysis of Cobalt(III) 14-Membered Macrocyclic Complexes

The configurational distribution of all the cobalt(III) complexes containing a 14-membered tetra-aza macrocyclic backbone in the Cambridge Structural Database was determined by cluster analysis, and the reason for some of the complexes adopting their configuration was established by molecular mechanics.     

Room Temperature Ring Expansion of N‐Heterocyclic Carbenes and BB Bond Cleavage of Diboron(4) Compounds

We report the isolation and detailed structural characterization, by solid‐state and solution NMR spectroscopy, of the neutral mono‐ and bis‐NHC adducts of bis(catecholato)diboron (B₂cat₂). The bis‐NHC adduct undergoes thermally induced rearrangement, forming a six‐membered ‐B?C?N?C?C‐N‐heterocyclic ring via C?N bond cleavage and ring expansion of the NHC, whereas the mono‐NHC adduct is stable. Bis(neopentylglycolato)diboron (B₂neop₂) is much more reactive than B₂cat₂ giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis.     

Generation of Aryl Radicals through Reduction of Hypervalent Iodine(III) Compounds with TEMPONa: Radical Alkene Oxyarylation

A novel method for selective generation of aryl radicals from diaryliodonium salts and iodanylidene malonates with sodium 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPONa) as a single‐electron transfer (SET) reducing reagent is described. In the presence of various alkenes, aryl radicals formed after SET‐reduction of hypervalent iodine compounds undergo alkene addition and the adduct radicals that are thus generated are efficiently trapped by the concomitantly generated TEMPO radical to eventually afford oxyarylated products in moderate to very good yields. The efficiency of aryl radical generation of various iodine(III) reagents is studied and the generation of an iodanylidene malonate aryl radical is also investigated by computational methods.     

Cobalt(III)‐Catalyzed Dehydrative [4+2] Annulation of Oxime with Alkyne by CH and NOH Activation

Efficient, scalable cobalt‐catalyzed redox‐neutral [4+2] annulation of readily available oximes and alkyne is reported. The developed synthetic methodology is widely applicable and tolerates various functional groups including heterocycles. A stable Cp*Co^III neutral complex is employed as the catalyst for this redox‐neutral [4+2] annulation reaction, which progresses smoothly by way of a reversible cyclometallation without any external oxidizing agent, and produces only water as the side product.     

Synthesis and Crystal Structure of Cobalt(Ⅲ) Tris(diethyldithiocarbamato) Complex

1INTR0DUCTI0NRecently,thedesignandsynthesisofdinuclearcomplexeshavebeenafascinat-ingareaofresearchowingt0theirimportanceinbasicandappliedchemistry"'.Par-ticularintersthasdevelopedindinuclearcomplexesasmodelsformeta1loproteins"'.Inanattempttosynthesizethetypeof[Ln(S,CN(C2H,)2)3j[Co(S2CN(C2H5)2)2jdinuc1earcomplex,thepurefinecrystalsofCo[S2CN(C2H5)2)2)3were0btained.2EXPERIMENTAL2'1Preparation0fC0[S,CN(C,H,),j,TotheclearsolutionoftheanhydrousSmCl3(0.5mmol)in5mLanhydrousethanolw…     

Cobalt(III)‐Catalyzed Directed CH Coupling with Diazo Compounds: Straightforward Access towards Extended π‐Systems

The first highly efficient and scalable cobalt‐catalyzed directed C? H functionalization with carbene precursors is presented. This methodology provides a modular route towards a new class of conjugated polycyclic hydrocarbons with tunable emission wavelengths both in solution and in the solid state.     

Cobalt(I)-mediated preparation of polyborylated cyclohexadienes: scope, limitations, and mechanistic insight

A series of 1,3- and 1,4-diboryl-1,3-cyclohexadienes have been prepared by intermolecular CoCp-mediated [2+2+2] cocyclizations of alkynylboronic pinacolate esters with alkenes, followed by oxidative demetallation with iron(III) chloride. The effect of substitution at the borylated alkyne on chemo- and regioselectivities has been studied, suggesting steric control. The proper choice of substituents allowed the preparation of 1,3-diborylated cyclohexadienes in a highly selective manner. Alternatively, 1,4-diborylated cyclohexadienes could be prepared from diborylated diynes. The scope of this reaction has been examined and found to include electron-poor, electron-rich, linear, and cyclic alkenes. The diborylated cyclohexadienes were submitted to single or double Suzuki-Miyaura cross-coupling reactions with haloarenes to afford polyarylated systems. The mechanism of the title reaction, including the regioselectivity of the cycloaddition steps, has been analyzed by means of DFT computations.