Dicobalt Complexes Research Articles

Metal Complexes of Peptides. VI. Di-μ-hydroxo–Dicobalt(III) Complexes Containing Peptides

Abstract Two isomers of the dinuclear complex with β-alanyl-l-aspartate (β-ad), glycinate (gly), and ethylenediamine (en), [Co(β-ad)Co(gly)(en)(μ-OH)2]+, were prepared by treating an aqueous solution containing [Co(β-ad)(OH2)2] and [Co(gly)(en)(OH2)2]2+ under basic conditions. The geometrical structures and absolute configurations of these isomers were assigned on the basis of the NMR, UV, and CD spectral data; the assignments were confirmed on the basis of the spectral data of the mononuclear species that were obtained by the acid hydrolysis of the isomers. The faster eluted isomer (eluted with H2O on an SP-Sephadex (K+ form) column) consists of [Co(β-ad)(μ-OH)2] (β-ad coordinates to cobalt(III) as a tetradentate) and Δ-fac(O)-[Co(gly)(en)(μ-OH)2] moieties, and the later consists of [Co(β-ad)(μ-OH)2] and Λ-fac(O)-[Co(gly)(en)(μ-OH)2]. Another di-μ-hydroxo–dicobalt(III) complex containing β-alanyl-l-histidinate (car), [Co2(car)2(μ-OH)2], was also prepared by treating an aqueous solution containing [Co(car)(OH2)2]+ under basic conditions. The dinuclear structures of these complexes are stable for several days in the neutral aqueous solutions.

μ2-N pseudohalide as mediator of magnetic exchange in dicobalt(II) complexes

Ferromagnetic interaction mediated via 1,1-azido-bridging in two macrocyclic Co(II) (6-coordinate and 4-coordinate) complexes is insensitive to ground state of Co(II); in the analogous 1,1-cyanato complexes, the interaction is weak and in the opposite sense.

NEW MACROCYCLIC LIGANDS [28]ane-N6O2 and [26]ane-N6O2 AND THEIR MONONUCLEAR AND DINUCLEAR COMPLEXES

Abstract Two new macrocycles, [28]ane-N6O2 and [26]ane-N6O2, have been synthesized, purified and characterized. The protonation constants of the ligands and the formation constants of their mononuclear and dinuclear metal complexes with Cu(II), Ni(II), Zn(II) and Co(II) were measured potentiometrically at 25.0°C and ionic strength 0.10 M (KCl). Compared with the other transition metal dinuclear chelates, the dicopper complexes are relatively stable in aqueous solution. The hydroxo-bridged monohydroxo dinuclear copper(II) complex forms through a dissociation of a proton from coordinated water. Potentiometric p[H] measurements on the dicobalt(II) complex of [26]ane-N6O2 demonstrate formation of a hydroxo-bridged μ-peroxo type dioxygen complex with a water molecule coordinated to each cobalt center.

Bimetallic Reactivity. Synthesis of Bimetallic Complexes of Macrocyclic Binucleating Ligands Containing 6- and 4-Coordinate Sites and Their Reactivity with Dioxygen and Other Oxidants

General methods are described for the synthesis of amine macrocyclic ligand systems which can contiguously accommodate two metals, one in a 6-coordinate site and the other in a 4-coordinate location. The amine complexes of the type [M(amine ligand)(H+)2]n+, where M is in the 6-coordinate site and the other site contains two protons, are obtained from the previously described imine complexes, [M(imine ligand)(H+)2]n+, by BH4- reduction. The macrocyclic framework consists of two diamine links, one at each site. Ligands incorporating the trimethylenediamine (tn) and ethylenediamine (en) links were prepared, namely, the four ligands containing the tntn, tnen, entn, and enen combinations. Bimetallic complexes of the amine ligands are prepared under mild conditions from the monometallic complexes [M(amine ligand)(H+)2]n+ by addition of the second metal. The structures of these complexes were studied by 1H NMR spectrometry and by X-ray diffraction. The monometallic imine complexes, [CoII(imine ligand)(H+)2]2+, are oxidized to cobalt(III) complexes by ferrocinium ions (fc+) when en links are present in the 6-coordinate site but this is not the case when tn is present in this site. All of the amine complexes, [CoII(amine ligand)(H+)2]2+, are oxidized by fc+ to give stable cobalt(III) complexes and it is concluded that the rigidity of the imine ligands prevents the ligand from adjusting to the stereochemical demands of cobalt(III) when the 6-coordinate site contains the larger tn link in the imine systems. This stereochemical impediment is relaxed in the more flexible amine systems. This effect is called mechanical coupling. Ferrocinium ion oxidation of the bimetallic amine complexes, [CoII(amine ligand)CoIICl]+, leads only to the formation of the mixed oxidation state complexes, [CoIII(amine ligand)CoIICl]2+, where the cobalt(III) is in the 6-coordinate site. Unlike the imine dicobalt(II) complexes which are unreactive to dioxygen, the amine ligand dicobalt(II) complexes readily react with dioxygen to give the mixed oxidation state complexes, [CoII(amine ligand)CoIII(Cl)(X)]+, where now the cobalt(III) ion occupies the 4-coordinate site. The inability to form stable dicobalt(III) complexes with these amine ligands, despite the fact that each site is capable of supporting the cobalt(III) states, is ascribed to various forms of coupling between the metals in the two sites. Three forms of coupling are considered and discussed; these are, mechanical coupling which refers to ligand constraints, through-space electrostatic interactions between metals, and through-bond coupling which refers to covalent interaction between the metals via the bridging ligands.

Preparation and Characterization of Cobalt(II) Complexes Derived from Hexadentate ‘Tripod’ Ligand and Their Potentials as Epoxidation Catalysts

Abstract The ligand N,N,N'N'-tetrakis(1-hydroxymethyl-2-benzimidazolylmethyl)-1,2-ethanediamine (HMEDTB) (L) has been prepared and characterized by elemental analyses and spectral data. Its reaction with cobalt(II) chloride hexahydrate, or cobalt(II) nitrate hexahydrate in the molar ratio of 1:2 in acetonitrile afforded the complexes [Co(L)]2+ 2NO3 − (1), and [Co2(L)Cl2]2+ 2Cl− (2), respectively. Elemental analyses and spectral data on compound (1) show it to be a mononuclear cationic cobalt(II) complex in an octahedral geometry, with two nitrate ions as counterions. Similar data on compound (2) reveal the presence of a cationic dicobalt complex with bridging hydroxide in possibly a trigonal bipyramidal geometry. Compounds (1) and (2) catalysed the epoxidation of styrene in 53.8 and 34.3% yields, respectively.

Ligand-mediated metal-metal interactions in ( ν5: ν5-fulvalene) bis (dicarbonylcobalt) and rhodium complexes

Gas phase photoelectron spectroscopy (PES) is used to investigate the bonding and electronic structure in (fv) [M(CO) 2] 2 (fv = fulvalene, η 5: η 5-C 10 H 8 2−; M = Co, Rh). The results for these bimetallic complexes are also compared to those for the analogous monometallic complexes CpM(CO) 2 (Cp = η 5−C 5H 5 −; M = Co, Rh) which have been reported previously. The low valence ionization patterns observed for CpCo(CO) 2 and (fv)[Co(CO) 2] 2 are very similar, indicating that there is little electronic interaction between the two metals of the dicobalt complex. The spectrum of (fv)[Rh(CO) 2] 2 also is very similar to the spectrum of CpRh(CO) 2, except that the first metal ionizations in the bimetallic rhodium compound show a significant splitting (0.45 eV). This splitting is due to electronic interaction between the two metal centers which occurs via communication through the fulvalene π system. The differences in electronic structure are compared to the differences in electrochemical behavior of the Co and Rh fulvalene complexes.

Synthesis and crystal structure of a novel dinuclear complex of cobalt(II) with a new benzimidazole-containing azacycle ligand

A novel dicobalt(II) complex Co 2Cl 4L 2 · C 2H 5OH was obtained, where L is [4′-(2″-methylene-benzimidazole-yl)-1′,4′-dinitrogencyclohexane] 1,2-benzimidazole, a new azacycle ligand. The single crystal structure of the complex was determined by X-ray diffraction. Two nitrogen and two chloride atoms are around each cobalt with tetrahedral geometry. Each L bonds two cobalt atoms through its two benzimidazole groups.

Radikalreaktionen von 6,6-DimethylfuIven am paramagnetischen Cobalt(0)-Zentrum -Struktur eines Dicobaltkomplexes mit tetramerem Kohlenwasserstoff-Liganden / Radical Reactions of 6 ,6 -Dimethylfulvene at Paramagnetic Cobalt(O) Centers - Structure of a Dicobalt Complex Containing a Tetrameric Hydrocarbon Ligand

6,6-Dimethylfulvene reacts with Co(C2H4)(PMe3)3 to give a diamagnetic dicobalt complex containing a novel bis (η5,η2)-chelating hydrocarbon ligand which is a tetramer of 6,6-dimethylfulvene. C,C-coupling via radicals induces multiple chirality in the ligand and the structurally characterized stereoisomer adopts a (S,R,R,S) configuration (m eso form).

Preparation and crystal structure of anti-(η 3:η 3-azulene)pentakis(trimethylphosphine)dicobalt. Reactions with carbon monoxide and solution dynamics

Azulene dicobalt complexes [ anti-1,2,3,9,10-η 5:4,5,6-η 3-C 10H 8]Co 2(CO) n (PMe 3) 5− n ( n=0 ( 1); 1 ( 2); 3 ( 3)) have been synthesized by reaction of olefintris(trimethylphosphine)cobalt(0) with azulene under ambient conditions followed by treatment with stoichiometric amounts or excess of carbon monoxide, respectively. X-ray structural data for 1 show a cyclopentadienyl-type η 5-coordination of a Co(PMe 3) 2 group and an η 3-allyl coordination of a Co(PMe 3) 3 group to the five- and seven-membered rings of azulene, respectively, while a vinylic CC bond remains uncoordinated. Temperature dependent proton resonances of the azulene ligand in 1– 3 are explained by Co(ligand) 3 groups fluctuating between two equivalent sites above the seven-membered ring.

Iso- and mixed-valent phenoxy bridged binuclear macrocyclic complexes of cobalt, iron and manganese

The binuclear complexes of a tetraaminodiphenol macrocyclic ligand (H 2L) of cobalt(II) and manganese(II) with the composition [M 2LX 2]βH 2O (X = Cl or Br) and of iron(II) with the composition [Fe 2L(imidazole) 2(CH 3OH) 2](ClO 4) 2·2CH 3OH have been synthesized and spectroscopically characterized. Cyclic voltammetric measurements of the dicobalt(II) complexes have indicated that the generation of Co III-Co II and Co III-Co III species take place quasi-reversibly or irreversibly at about 0.38 and 0.90 V vs SCE, respectively. The dimanganese(II) complexes undergo quasi-reversible one-electron oxidation at about 0.32 V, but further oxidation does not occur up to 1.2 V. The iron(II) complex irreversibly gets oxidized at ca 1 V. The dicobalt(II) and dimanganese(II) complexes can be oxidized with bromine and the mixed-valence complexes [M IIIM IILCl 2Br(CH 3OH)]·solvent have been isolated. Variable-temperature magnetic measurements of [Co IIICo IILCl 2Br (CH 3OH)]·0.5CH 2Cl 2, [Mn 2 IILBr 2(CH 3OH) 2]·H 2O and [Fe 2 IIL(imidazole) 2(CH 3OH) 2] (ClO 4) 2·2CH 3OH have indicated that the mixed-valence cobalt complex behaves as a S = 3 2 system, while both the diiron(II) and dimanganese(II) complexes exhibit antiferromagnetic exchange coupling with J = −6.3 and −6.1 cm −1, respectively.

Molecular Recognition within a Rigid Host: Structural Changes Induced in μ‐Carboxylato Dimetal(II) Complexes by Replacing Steric Repulsions with Hydrogen Bonds

Small change-large effect. When two Nmethyl groups on one N atom are replaced by hydrogen atoms in each of the diamino hgands in 1, M = Co, the bridging aqua ligand is ousted and an asymmetric dicobalt complex with one five-coordinate, one six-coordinate metal center, and three bridging carboxylato ligands results. This type of structural tuning is important for modeling, for example, the metal coordination environment in diiron(ii) non-heme proteins in which a coordination site on one metal is open.

Diiron and dicobalt complexes of a phenolate-bridged binucleating ligand with mixed phenolate and pyridine podands

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDiiron and dicobalt complexes of a phenolate-bridged binucleating ligand with mixed phenolate and pyridine podandsV. D. Campbell, E. J. Parsons, and W. T. PenningtonCite this: Inorg. Chem. 1993, 32, 9, 1773–1778Publication Date (Print):April 1, 1993Publication History Published online1 May 2002Published inissue 1 April 1993https://doi.org/10.1021/ic00061a038RIGHTS & PERMISSIONSArticle Views259Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (785 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Photochemical synthesis and crystal structures of tetrakis(ethane-1,2-diamine) dicobalt(III) complexes bridged by 1,3,5-triazine-2,4,6-trithionate and 4-oxo-1,3,5-triazine-2,6-dithionate

Two kinds of dinuclear cobalt(III) complexes sym-(meso- and rac-)[{Co(en)2}2(µ-ttcy)]X3 and sym-[meso- and rac-)[{Co(en)2}2(µ-dtcy)]X3(en = ethane-1, 2-diamine, H3ttcy = 1,3,5-triazine-2,4,6-trithione, H3dtcy = 4-oxo-1,3,5-triazine-2,6-dithione) have been prepared photochemically from [Co(en)3]Cl3, H3ttcy and NaOH and characterized by elemental analysis, IR, UV/VIS and NMR spectroscopy. The dtcy complexes are formed via a novel desulfurization of the ttcy ligand. Two crystal structures, sym-meso-[{Co(en)2}2(µ-ttcy)][ClO4]3·2H2O and sym-meso-[{Co(en)2}2-(µ-dtcy)]l3·4H2O were determined from 1859 and 4146 reflections to R= 0.056 (R′= 0.060) and R= 0.069 (R′= 0.073), respectively: monoclinic, space group P21/a, a= 14.392(4), b= 14.807(4), c= 14.816(4)A, β= 92.83(3)° and Z= 4; monoclinic, space group P2/c, a= 18.088(3), b= 8.146(6), c= 21.757(3)A, β= 93.25(1)° and Z= 4. The bridging ttcy and dtcy ligands co-ordinate symmetrically through the two N and S donor sets and both complexes are in the meso form. Marked symmetric intramolecular hydrogen bonds N–H ⋯ S[N ⋯ S 3.19(1), 3.21(1)A] were formed between the free sulfur atom of the ttcy and the two amine protons of the en in the ttcy complex.

Dioxygen activation by [Co2(µ-OH)L]{H3L=2,6-bis[(2-hydroxyphenyl)iminomethyl]-4-methylphenol}, catalysed cooxygenation of PPh3and alkenes, alcohols, a sulfide, a sulfoxide and diphenylacetylene

Alkenes, alcohols, a sulfide, a sulfoxide and diphenylacetylene can be hetero-cooxygenated with PPh3 catalysed by a dicobalt complex: [Co2(µ-OH)L]{H3L = 2,6-bis[(2-hydroxyphenyl)iminomethyl]-4-methylphenol}, to produce a single oxidation product for each substrate.

Oxidatively induced alkyne rotation in dicobalt complexes: structural tests of molecular orbital theory

The complexes [Co2(CO)2(µ-RC2R)(µ-dppm)2]1(R = Me, Ph or CO2Me; dppm = Ph2PCH2PPh2) undergo reversible one-electron oxidation at a platinum-bead electrode in CH2Cl2; chemical oxidation of 1 with the ferrocenium ion or with iodine gives stable salts of the monocations 1+. The X-ray structures of 1(R = Me and Ph) show the alkyne bridge to be orthogonal to a cobalt–cobalt bond which is also bridged by the two dppm ligands. The overall structure of 1+(R = Me), as its [PF6]– salt, is similar but with the alkyne bridge rotated by 12° about an axis perpendicular to the shortened metal–metal bond. The structural changes observed provide direct experimental support for previous bonding studies of the structural preferences of hydrocarbon-bridged M2(CO)6 complexes.

Reactions of decakis(isopropylisocyanide)dicobalt(II) complexes with tertiary phosphine ligands

Reaction of [Co 2(CNCHMe 2) 10]X 4· nH 2O (XClO 4, BF 4) with triarylphosphines and substituted trialkylphosphines produces disubstituted Co(I) complexes, [Co(CNCHMe 2) 3(PR 3) 2]X; R  C 6H 5, C 6H 4Cl- p, C 6H 4OMe- p, CH 2C 6H 5, NMe 2, CH 2CH 2CN. These reduction/ligand-substitution reactions are analogous to those of [Co(CNCMe 3) 4H 2O](ClO 4) 2. Reaction with unsubstituted trialkylphosphines produces Co(III) complexes, [Co(CNCHMe 2) 4(PR 3) 2]X 3; R  C 4H 9-n, C 6H 13-n; in disproportionation reaction from which the Co(I) complex is not recovered: [CO 2(CNCHMe 2) 10]X 4+4PR 3 → [Co(CNR) 4(PR 3) 2]X 3+ [Co(CNR) 3(PR 3) 2]X+3CNR. Solution properties (ν(  NC), electronic spectra, Λ M) are compared for CNCHMe 2 and CNCMe 3 complexes. The Co(I) complexes are 1:1 electrolytes in CH 3CN, CH 3NO 2, CH 3C(O)CH 3 and CH 2Cl 2; the Co(III) complexes are 3:1 electrolytes in CH 3CN and CH 3NO 2, but exhibit increasing ion-pairing in acetone and CH 2Cl 2. The ν( NC) suggest decreasing π *-acceptance in the order: CNCHMe 2 ⪢ P(C 6H 4Cl- p) 3 > P(C 6H 5) 3 ≥ P(CH 2CH 2CN) 3 > P(C 6H 4OMe- p) 3 > P(CH 2Ph) 3 > P(NMe 2) 3. Solution structure for [Co(CNCHMe 2) 3(PR 3) 2]X is believed to be distorted trigonal bipyramidal, but rigorous D 4h for [Co(CNCHMe 2) 4(PR 3) 2]X 3.

Heterometallische Cluster durch ligandunterstützte Metallfragmentkondensation / Heterometallic Clusters by Ligand Assisted Metal Fragment Condensation

Dicobalt complexes of 3-vinylpropargylic alcohol derivatives react with biscyclooctenetricarbonyliron to give new chelate complexes of the iron tricarbonyl fragment with the olefinic double bond and the alcohol oxygen atom bound to the iron fragment. These compounds react upon heating in an inert solvent to give FeCo-alkynyl cluster complexes in high yields. One of these compounds has been structurally characterized by X-ray crystallography.

The synthesis of new binucleating polyaza macrocyclic and macrobicyclic ligands: dioxygen affinities of the cobalt complexes

Six macrocyclic and five macrobicyclic Schiff bases have been synthesized by condensation of rigid dialdehydes with diethylenetriamine or tris (aminoethyl) amine, and have been reduced to the corresponding saturated hexaaza macrocyclic complexes or octaaza macrobicyclic complexes. Six of the dicobalt complexes of these new ligands were found to be oxygen carriers.

Synthesis and chemistry of dynemicin A models

The synthesis of the model systems 10 and 22 of dynemicin A (2) containing the nitrogen, enediyne, and epoxide functionalities ahs been achieved. These models are shown to undergo acid-induced triggering to give the corresponding Bergman-cyclized products in the presence of suitable H atom donors. Removal of the N protecting group from 22 gave the unstable qfree amine 30, which was shown to cause double-stranded-DNA cleavage, presumably in a manner similar to that of dynemicin A (2) itself. Some interesting chemistry related to dicobalt complexes of the enediynes is also presented

Synthesis, geometrical and absolute configuration of the tris(S-arginine)cobalt(III) trinitrate isomers and synthesis and molecular structure of (-)589-anti(N)-Δ-cis(N),cis(O)-Λ-cis(N),cis(O)-di-μ-hydroxo-tetrakis(S-arginine)dicobalt(III) tetranitrate tetrahydrate

In a direct synthesis reaction of the tris(aminocarboxylato)cobalt(III) complexes with S-arginine all four theoretically possible tris(S-arginine)cobalt(III) diastereomers were obtained as tripositive complex ions. Besides, one out of 24 theoretically possible isomers of di-μ-hydroxo-tetrakis(S-arginine)dicobalt(III) tetrapositive ion was obtained. Geometrical and absolute configurations of the tris(S-arginine)cobalt(III) isomers were determined by electronic and CD spectroscopy. The molecular structure of the (-)589-anti(N)-Δ-cis(N),cis(O)-Λ-cis(N),cis(O)-di-μ-hydroxo-tetrakis(S-arginine)dicobalt(III) ion was solved by X-ray crystal structure analysis. The complexes obtained represent the first examples of cationic aminocarboxylato complexes of this type. For the first time the formation of the di-μ-hydroxo-tetrakis(aminocarboxylato)dicobalt(III) complex has been observed as a reaction concurrent to the formation of tris(aminocarboxylato)cobalt(III) complexes. Finally, the stereoselectivity of S-arginine in the tris(S-arginine)cobalt(III) isomers synthesis was discussed.