Tetramethylcyclobutadiene)cobalt complexes of protected aromatic amino acids*

Reactions of [(C4Me4)Co(MeCN)3]PF6 with aromatic amino acid derivatives give the arene complexes [(C4Me4)Co(amino acid)]PF6 (amino acid = ethyl ester of N-acetylphenylalanine, N-acetyltyrosine or N-acetyltryptophan) in 75–85% yields; the structure of the tyrosine complex was determined by X-ray diffraction.     

Experimental and theoretical charge density distribution in two ternary cobalt(III) complexes of aromatic amino acids

The experimental charge density distributions in two optically active isomers of a Co complex have been determined. The complexes are Delta-alpha-[Co(R,R-picchxn)(R-trp)](ClO4)2.H2O) (1) and Lambda-beta1-[Co(R,R-picchxn)(R-trp)](CF3SO3)2) (2), where picchxn is N,N'-bis(2-picolyl-1,2-diaminocyclohexane) and R-trp is the R-tryptophane anion. The molecular geometries of 1 and 2 are distinguished by the presence in complex 1 of intramolecular pi...pi stacking interactions and the presence in complex 2 of intramolecular hydrogen bonding. This pair of isomers therefore serves as an excellent model for studying noncovalent interactions and their effects on structure and electron density and the transferability of electron density properties between closely related molecules. For complex 2, a combination of X-ray and neutron diffraction data created the basis for a X-N charge density refinement. A topological analysis of the resulting density distribution using the atoms in molecules methodology is presented along with d-orbital populations, showing that the metal-ligand bonds are relatively unaltered by the geometry changes between 1 and 2. The experimental density has been supplemented by quantum chemical calculations on the cobalt complex cations: close agreement between theory and experiment is found in all cases. The energetics of the weak interactions are analyzed using both theory and experiment showing excellent quantitative agreement. In particular it is found that both methods correctly predict the stability of 2 over 1. The transferability between isomers of the charge density and derived parameters is investigated and found to be invalid for these structurally related systems.     

Characterization of an NH-pi interaction in Co(III) ternary complexes with aromatic amino acids

The NH-pi interaction has been detected in the crystal structures of Co(III) ternary complexes with N,N-bis(carboxymethyl)-(S)-phenylalanine (BCMPA) and aromatic amino acids including (S)-phenylalanine ((S)-Phe), (R)-phenylalanine ((R)-Phe), and (S)-tryptophan ((S)-Trp)). Additionally, this interaction has been studied in solution for Co(III) ternary complexes with BCMPA or NTA (NTA = nitrilotriacetic acid) and several amino acids (AA) by means of electronic absorption, circular dichroism (CD), and (1)H NMR spectroscopies. The CD intensities of the Co(III) complexes with aromatic amino acids measured in the d-d region ( approximately 20.5 x 10(3) cm(-)(1)) are significantly decreased in ethanol solutions relative to water. Analogous complexes with aliphatic amino acids do not exhibit this solvent effect. The (1)H NMR spectra of the Co(III) complexes with aromatic amino acids measured in DMSO-d(6) exhibit upfield shifts of the NH peaks compared with those with aliphatic amino acids, which suggest a shielding effect due to the aromaticity. The upshift values coincide with those experimentally evaluated from the crystal structures. The magnitude of the upfield shifts agrees well with Hammett's rule, indicating that the increase of pi-electron densities on the aromatic rings leads attractive NH-pi interaction that exerts a larger shielding effect for the NH protons. In ligand-substitution reactions of the carbonatocobalt(III) complexes with amino acids, the yields of those with aromatic amino acids are higher than the yields obtained for complexes with aliphatic amino acids. This observation is discussed in connection with the important contribution of the NH-pi interaction as one of the promotion factors in the reaction.     

Properties of fluoroantimonates(III) complexes with amino acids

Crystalline complex fluoroantimonates(III) with amino acids (glycine, β-alanine, DL-serine, DL-valine, L-leucine, and L-phenylalanine) have been prepared. The complexes stability in aqueous solutions has been studied with the cementation method. ¹H NMR studies of aqueous solutions of the amino acids complexes with SbF₃ at pH 1–6 and room temperature are reported. Preparation of polycrystalline metal antimony in aqueous solutions of tetrafluoroantimonates(III) complexes with the protonated amino acids has been demonstrated.     

Iron(III) complexes of salicylidene amino acids

Several iron(III) complexes of tridentate dibasic salicylidene/substituted salicylidene amino acids (ONO donor set) have been prepared and characterized. All iron(III) compounds possess dimeric pseudo — octahedral structure established on the basis of elemental analysis, magnetic moment studies, superimposable infrared spectra of these complexes with those of nickel(II), cobalt(II), manganese(II), magnesium(II) and zinc(II) complexes, and thermogravimetric analysis.

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Zusammenfassung Mit dreizahnigen dibasichen substituierten und unsubstituierten Salizylidenaminosäuren (ONO Donorset) wurden einige Eisen(III)-komplexe hergestellt und diese beschrieben. Mittels Elementaranalyse, TG-Analyse, der Untersuchung des magnetischen Momentes und des Vergleiches von IR-Spektren mit denen von Nickel(II)-, Cobalt(II)-, Mangan(II)-, Magnesium(II)- und Zink(II)-komplexen konnte festgestellt werden, daß alle Eisen(III)-komplexe über eine pseudooktaedrische Dimerenstruktur verfügen.

     

Chromium(III) complexes of naturally occurring amino acids

Summary Amino acid complexes of CrCl₃Py₃ have been prepared and studied by elemental analysis, magnetic susceptibility, vibrational (i.r.), electronic and circular dichroism spectroscopy. Two peaks in the visible spectra are assigned to a d-d transition in pseudo octahedral symmetry. The spectrochemical parameters (Dq, B and ₃₅) for the complexes were calculated which confirm that pyridine nitrogen and/or chlorine are not removed. Prolonged heating or bubbling of air through the solution of CrCl₃-Py₃ containing l-(-)-histidine or l-(-)-threonine for several hours enhanced formation of chromium (VI).     

Supramolecular formation by aromatic ring stacking and hydrogen bonding in lanthanide(III) complexes with amino acids and 1,10-phenanthroline

[Eu(ABA)(phen)₂(H₂O)₃](ClO₄)₃·3phen·4.5H₂O (1) and [Eu(Val)(phen)₂(H₂O)₃](ClO₄)₃·3phen·2H₂O (2) are two new europium complexes with amino acids and 1,10-phenanthroline (phen=1,10-phenanthroline, ABA=-amino butyl acid, Val= -valine). Their crystal structures were measured by X-ray crystallography. Europium atoms in both complexes are nine-coordinated with bidentate 1,10-phenanthroline and carboxylate anion of amino acids, and water molecules. In the solid state, 1 and 2 have a structure involving aromatic stacking of the coordinated and non-coordinated 1,10-phenanthroline and the oxygen atoms of non-coordinated perchlorate anions being H-bond acceptors connect [Eu(ABA)(phen)₂(H₂O)₃]³⁺·3phen·4.5H₂O or [Eu(Val)(phen)₂(H₂O)₃]³⁺·3phen·2H₂O in their structures. In their interactions, several C–HO bonds play an important role. Owing to their different amino acid ligands and the number of lattice water molecules, there is some difference in their hydrogen bond patterns in 1 and 2. The side chain of -valine is involved in the formation of C–HO bonds. Hydrogen bond and π–π interactions determine the supramolecular formation of three-dimensional net works of both complexes.     

Thermal studies on oxalate complexes. III. Complexes of cobalt(III) and cobalt(II)

The decomposition of K₂[Co(C₂O₄)₂] and K₃[Co(C₂O₄)₃] has been studied using TG. In the case of the latter compound, the first step involves the rupture of all the oxalates and one of the resultant carbonates to liberate CO₂ and three molecules of CO. Subsequent steps involve the loss of CO₂. In the case of K₂[Co(C₂O₄)₂], four decomposition reactions are observed. The first involves the loss of only CO. Subsequent steps involve loss of CO₂, CO₂ and CO, and CO₂, respectively. Basic carbonates appear to be the intermediate products. Kinetic parameters are presented for most of the reactions.     

Tri­azido­cobalt(III) complexes with tridentate amine ligands

The title compounds, [N‐(2‐amino­ethyl)‐1,3‐propane­di­amine‐κ³N]­tri­azido­cobalt(III), [Co(N₃)₃(C₅H₁₅N₃)], [N‐(2‐amino­ethyl)‐N‐methyl‐1,3‐propane­di­amine‐κ³N]­tri­azido­cobalt(III), [Co(N₃)₃(C₆H₁₇N₃)], [N‐(2‐amino­propyl)‐1,3‐pro­pane­di­am­ine‐κ³N]­tri­azido­cobalt(III), [Co(N₃)₃(C₆H₁₇N₃)], and [N‐(2‐amino­propyl)‐N‐methyl‐1,3‐pro­pane­di­am­ine‐κ³N]triazidocobalt(III), [Co(N₃)₃­(C₇­H₁₉­N₃)], each consist of a Co^III atom, three azide ligands in a meridional configuration and a tridentate amine ligand, namely aepn [N‐(2‐amino­ethyl)‐1,3‐propane­di­amine] or dpt [N‐(3‐amino­propyl)‐1,3‐pro­pane­di­amine], or their N‐methyl­­ated analogs.     

Thermal decomposition of complexes of antimony(III) bromide with hydrobromides of some aromatic amines

Thermal studies have been carried out on crystalline complexes formed between antimony(III) bromide and hydrobromides of some aromatic amines in concentrated hydrobromic acid solutions. Thermal analysis curves of the compounds under study are presented. Kinetic parameters of the thermal decomposition reactions were calculated from the TG curves using the Horowitz—Metzger method. A comparison of the thermal stabilities of the complexes was made.     

Mixed ligand complexes of copper(II) involving amino acids and peptides

Summary The formation and stability of the mixed-ligand complexes of copper(II) with diethylenetriamine (dien) and amino acids or peptides have been investigated by potentiometric and conductometric techniques. The results indicate that the apical coordination of the ionized amide group of the peptide and the ionized alcoholatogroup of the amino acid is not possible.     

Cyano­cobalt(III) complexes of penta‐ and tetra­dentate‐coordinated macrocyclic hexa­amines

The pendent‐arm macrocyclic hexa­amine trans‐6,13‐dimethyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane‐6,13‐diamine (L) may coordinate in tetra‐, penta‐ or hexa­dentate modes, depending on the metal ion and the synthetic procedure. We report here the crystal structures of two pseudo‐octa­hedral cobalt(III) complexes of L, namely sodium trans‐cyano­(trans‐6,13‐dimethyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane‐6,13‐diamine)cobalt(III) triperchlorate, Na[Co(CN)(C₁₃H₃₀N₆)](ClO₄)₃ or Na{trans‐[CoL(CN)]}(ClO₄)₃, (I), where L is coordinated as a penta­dentate ligand, and trans‐dicyano­(trans‐6,13‐dimethyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane‐6,13‐diamine)cobalt(III) trans‐dicyano­(trans‐6,13‐dimethyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane‐6,13‐diaminium)cobalt(III) tetra­perchlorate tetra­hydrate, [Co(CN)₂(C₁₄H₃₂N₆)][Co(CN)₂(C₁₄H₃₀N₆)](ClO₄)₄·4H₂O or trans‐[CoL(CN)₂]trans‐[Co(H₂L)(CN)₂](ClO₄)₄·4H₂O, (II), where the ligand binds in a tetra­dentate mode, with the remaining coordination sites being filled by C‐­bound cyano ligands. In (I), the secondary amine Co—N bond lengths lie within the range 1.944 (3)–1.969 (3) Å, while the trans influence of the cyano ligand lengthens the Co—N bond length of the coordinated primary amine [Co—N = 1.986 (3) Å]. The Co—CN bond length is 1.899 (3) Å. The complex cations in (II) are each located on centres of symmetry. The Co—N bond lengths in both cations are somewhat longer than in (I) and span a narrow range [1.972 (3)–1.982 (3) Å]. The two independent Co—CN bond lengths are similar [1.918 (4) and 1.926 (4) Å] but significantly longer than in the structure of (I), again a consequence of the trans influence of each cyano ligand.     

Preparation and photochemistry of cobalt(III) amino and amino acidato complexes containing tripodal polypyridine ligands

The photochemical reactivities of cobalt(III)-diamine and cobalt(III)-amino acid compounds have been compared using complexes that also contain polypyridyl ligands. Metallacyclic complexes result from UV-induced photodecarboxylation reactions of the amino acid complexes. UV-irradiation of closely related complexes with amine donors replacing the carboxylate donors does not lead to the production of the same metallacyclic products. The reported UV-induced fragmentation of amine donors and subsequent metallacycle formation appears not to be a general reaction. Nine cobalt(III) complexes of polypyridyl ligands have been structurally characterised, including four that also contain amino acid ligands and one that contains a three-membered metallacyclic ring.     

Reactivity trends of cobalt(III) complexes towards various amino acids based on the properties of the amino acid alkyl chains

The reactivity of the cobalt(III) complexes dichlorido[tris(2‐aminoethyl)amine]cobalt(III) chloride, [CoCl₂(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl₂(trien)]Cl, towards different amino acids (l ‐proline, l ‐asparagine, l ‐histidine and l ‐aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (l ‐prolinato‐κ²N,O)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) diiodide monohydrate, [Co(C₅H₈NO₂)(C₆H₁₈N₄)]I₂·H₂O, I , (l ‐asparaginato‐κ²N,O)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), II , and (l ‐prolinato‐κ²N,O)(triethylenetetramine‐κ⁴N,N′,N′′,N′′′)cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), V . The syntheses of the complexes were followed by characterization using UV–Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM.     

Bacterial activity of cobalt(III) complexes. Part IV: Diethylenetriaminemonoacetatocobalt(III) complexes

Summary The activities of the diethylenetriaminemonoacetatocobalt(III) complexes, [Co(en)(DTMA)]I₂, [CoX₂(DTMA)] and [CoCO₃(DTMA)]·H₂O (DTMA=diethylenetriaminemonoacetato or formally 3-amino-3, 6-diazaoctanato; en=ethylenediamine, X=Cl^–, NO ₂ ^– , NCS^–) were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases. Activities decrease in the order: [Co(NCS)₂(DTMA)]> [Co(NO₂)₂(DTMA)]>[Co(en)(DTMA)]I₂>[CoCl₂(DTMA)] >[CoCO₃(DTMA)]·H₂O. The antagonistic activities of the complexes were also studied.     

Cleavage by halogens of carboncobalt bonds in organometallic complexes of cobalt(III) : II. Organobis(dimethylglyoximato)cobalt(III) complexes

The reaction between organocobaloximes and ICl in chloroform has been studied. In absence of an excess of added chloride ion the reaction is electrophilic in character; in presence of an excess of chloride ion both oxidative dealkylation and radical attack can occur.     

N-monoaryldithiocarbamate cobalt(III) complexes(1)

Summary Diamagnetic cobalt(III) complexes of the type (RHNCS₂)₃Co [R = Ph, XC₆H₄ (X=p-Me,p-OMe,p-Cl,p-Br andp-I) and 2,4-Me₂C₆H₃] have been synthesised by reaction of the corresponding dithiocarbamate ammonium salts and hexaaquocobalt(II) chloride. Ligand field parameters calculated from visible spectral data indicate strong covalent character for the Co-S bond. The i.r. spectral data reveal that the CN bond in these dithiocarbamates has less double bond character compared to the corresponding dialkyldithiocarbamates.     

Kinetics and mechanism of transaldimination of amino acids and aromatic amines with pyridoxal

Kinetics and mechanism of transaldimination of amino acids and aromatic amines with pyridoxal have been studied by means of UV spectroscopy and polarimetry. It has been shown that aminal intermediates are formed in reaction of the Schiff’s bases with p-aminobenzoic acid and β-alanine. The structure of aminal and Schiff’s base is determined by the spatial arrangement of the amino acid and aromatic fragments with respect to the pyridine ring plane. The presence of OH and CH₂-OH groups in the o-positions in pyridoxal structure turns amino groups by 90° with respect to the pyridine ring. The scheme of Schiff’s bases transaldimination by amino acids and biological amines has been developed according to stereospecific, energy, and geometric factors.