Potentiometric Titrations and Nickel(II) Complexes of Four Topologically Constrained Tetraazamacrocycles

Abstract

The novel high spin Ni²⁺ complexes of the topologically constrained tetraazamacrocycles (1–4) [4,11-dimethyl-1,4,8,11 - tetraazabicyclo[6.6.2]hexadecane (1); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[6.5.2]pentadecane (2); 4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (3); racemic-4,5,7,7,11,12,14,14-octamethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (4)] show striking properties. Potentiometric titrations of the ligands 2 and 4 revealed them to be proton sponges, as reported earlier for 1 [1]. Ligand 3 is less basic, losing its last proton with a pK = 11.3(2). Despite high proton affinities, complexation reactions in the absence of protons successfully yielded Ni²⁺ complexes in all cases. The X-ray crystal structures of Ni(1)(acac)⁺, Ni(3)(acac)⁺ and Ni(1)(OH₂)₂ ²⁺ demonstrate that the ligands enforce a distorted octahedral geometry on Ni²⁺ with two cis sites occupied by other ligands. Magnetic measurements and electronic spectroscopy on the corresponding Ni(L)Cl₂ (L = 1–3) complexes reveal that all are high spin and six-coordinate with typical magnetic moments. In contrast, [Ni(4)Cl⁺] is five-coordinate with a slightly higher magnetic moment and its own characteristic electronic spectrum. The extra methyl groups on ligand 4 define a shallow cavity, sterically allowing only one chloride ligand to bind to the nickel(II) ion.     

Chiral recognition in the gas phase: Mass spectrometric studies of diastereomeric cobalt complexes

Results of mass analyzed ion kinetic energy (MIKE) spectra and kinetic energy release (KER) measurements of diastereomeric octahedral cobalt complexes indicate that these diastereomers can be distinguished in the gas phase. Four alkyl tartrate esters were complexed to cobalt trisacetylacetonate (Co(acac)₃) in the presence of a chiral auxiliary, RR- and SS-threohydrobenzoin. Different KER values of the product ion generated from [Co(acac)₂/D- or L-diisopropyl tartrate]⁺ reflect differences in the precursor ion structure. The dissociation pathway resulting in this product ion is believed to arise via a hydride transfer from the acetylacetonate ligand to the metal center with subsequent loss of neutral organic species. It has been established that two conditions are necessary for observation of chiral recognition in this system; (1) the cobalt complex must be octahedral and (2) a chemical kinetic resolving agent must be present during formation of the complex.     

An improved method for synthesizing antennary β-d-mannopyranosyl disaccharide units

The merits of an indirect protecting method for hydroxyl groups using allyl groups via allyloxycarbonyl groups in the synthesis of antennary β-d-mannopyranosyl disaccharides from β-d-galactopyranosyl disaccharides were studied. Regioselective allyloxycarbonylation and conversion reactions involving simultaneous double S_N2 nucleophilic substitution at C-2′ and C-4′ of benzyl O-[β-d-galactopyranosyl]-(1-4)-3,6-di-O-benzyl-2-deoxy-2-N-phthalimido-β-d-glucopyranoside were examined for comparison with the direct allylation method. The required β-d-mannopyranosyl disaccharide having proper protecting groups was obtained using this indirect method in 52% yield. In contrast, the reported direct allylation method using methyl O-(β-d-galactopyranosyl) disaccharide gave the corresponding β-d-mannopyranosyl disaccharide in only 7.5% yield.     

The gas‐phase ligand exchange of copper and nickel acetylacetonate,hexafluoroacetylacetonate and trifluorotrimethylacetylacetonate complexes

The gas‐phase ligand‐exchange reactions between Cu(II) and Ni(II) complexes containing the acetylacetonate (acac), hexafluoroacetylacetonate (hfac), and trifluorotrimethylacetylacetonate (tftm) ligands were investigated using a triple quadrupole mass spectrometer. The gas‐phase mixed‐ligand products of [Cu(acac)(tftm)]⁺, [Ni(acac)(tftm)]⁺, [Cu(hfac)(tftm)]⁺, and [Ni(hfac)(tftm)]⁺ were formed following the co‐sublimation of either homo‐metal or hetero‐metal precursors. The gas‐phase formation of [Cu(acac)(tftm)]⁺, [Cu(hfac)(tftm)]⁺, [Ni(acac)(tftm)]⁺, and [Ni(hfac)(tftm)]⁺ complexes is reported herein for the first time. The corresponding fragmentation patterns of these species along with those of Cu(tftm)₂ and Ni(tftm)₂ are also presented. Mass‐selected ion‐neutral reactions were investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymerization of 3‐ethynylthiophene with homogeneous and heterogeneous Rh catalysts

3‐Ethynylthiophene (3ETh) was polymerized with Rh(I) complexes: [Rh(cod)acac], [Rh(nbd)acac], [Rh(cod)Cl]₂, and [Rh(nbd)Cl]₂ (cod is η²:η²‐cycloocta‐1,5‐diene and nbd η²:η²‐norborna‐2,5‐diene), used as homogeneous catalysts and with the last two complexes anchored on mesoporous polybenzimidazole (PBI) beads: [Rh(cod)Cl]₂/PBI and [Rh(nbd)Cl]₂/PBI used as heterogeneous catalysts. All tested catalyst systems give high‐cis poly(3ETh). In situ NMR study of homogeneous polymerizations induced with [Rh(cod)acac] and [Rh(nbd)acac] complexes has revealed: (i) a transformation of acac ligands into free acetylacetone (Hacac) occurring since the early stage of polymerization, which suggests that this reaction is part of the initiation, (ii) that the initiation is rather slow in both of these polymerization systems, and (iii) a release of cod ligand from [Rh(cod)acac] complex but no release of nbd ligand from [Rh(nbd)acac] complex during the polymerization. The stability of diene ligand binding to Rh‐atom in [Rh(diene)acac] catalysts remarkably affects only the molecular weight but not the yield of poly(3ETh). The heterogeneous catalyst systems also provide high‐cis poly(3ETh), which is of very low contamination with catalyst residues since a leaching of anchored Rh complexes is negligible. The course of heterogeneous polymerizations is somewhat affected by limitations arising from the diffusion of monomer inside catalyst beads. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2776–2787, 2008     

Structural and Electronic Influences on Rates of Tertpyridine−Amine CoIII−H Formation During Catalytic H2 Evolution in an Aqueous Environment

In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co^II−Cl]⁺ species results in the formation of [Co^II(κ⁴-L)(OH₂)]²⁺. Further reduction produces [Co^I(κ⁴-L)(OH₂)]⁺, which undergoes a rate-limiting structural rearrangement to [Co^I(κ⁵-L)]⁺ before being protonated to form [Co^III−H]²⁺. The rate of [Co^III−H]²⁺ formation is similar for all complexes in the series. Using E_1/2 values of various Co species and pK_a values of [Co^III−H]²⁺ estimated from PR experiments, we found that while the protonation of [Co^III−H]²⁺ is unfavorable, [Co^II−H]⁺ reacts with protons to produce H₂. The catalytic activity for H₂ evolution tracks the hydricity of the [Co^II−H]⁺ intermediate.     

Microsolvation of the [Ni(acac)(tmen)]+ complex

Microsolvation of the [Ni(acac)(tmen)]⁺ complex by a series of aliphatic n-alcohols (Solv) has been studied in ClCH₂CH₂Cl solutions by spectrophotometry. Based on the changes in the electronic spectrum of the afore-mentioned complex, observed under the influence of any alcohol, the equilibrium constants for the formation of the [Ni(acac)(tmen)Solv]⁺ and [Ni(acac)(tmen)Solv₂]⁺ species have been computed according to the algorithm presented in this work. It was found that, in all the systems studied, the stability of five-coordinated [Ni(acac)(tmen)Solv]⁺ is higher than that of octahedral [Ni(acac)(tmen)Solv₂]⁺. The resulting values are discussed in terms of the Lewis basicity of alcohols.     

Differentiation of anomeric C-glycosides by mass spectrometry using fast atom bombardment,mass-analysed ion kinetic energy and collision-activated dissociation

Positive-ion fast atom bombardment mass spectrometry appears to be a useful method for the differentiation of anomeric C-glycosides. The mass-analysed ion kinetic energy (MIKE) and collision-activated dissociation (CAD) MIKE spectra of selected positive ions can be used as fingerprints of the α- or β-anomers. The main fragmentation routes and particularly the formation of the [M ? H]⁺ ion and the [M + H ? PhCH₂OH]⁺ ion were traced for each anomer.     

Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses

The ammonia desorption chemical ionization (NH₃-DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non-reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH₄ – 42]⁺ ion is not formed direct from [M + NH₄]⁺ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH₄⁺. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH₃CO to afford neutral species which complex with NH₄⁺. The structures of the ions resulting from H transfer have been inferred by comparison of their mass-analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH₄]⁺ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.     

Synthesis and Characterization of Mono- and Trinuclear Complexes of BF2+ Bridged Macrocycles

Dibenzo[e,k]-2,3-bis(hydroxyimino)-1,4-dithia-7,10-diaza-2,3,8,9-tetrahydrocyclododecine (H₂L) has been prepared from 1,2-bis(o-mercaptoanilino) ethane ( 4 ) and (E,E)-dichloroglyoxime. A mononuclear complex with a metal: ligand ratio of 1:2 has been isolated for cobalt(III). The Co^III complex of H₂L has been prepared with L′ = 2,6-lutidine, and with a chlorine ion as axial ligands. In addition to that, the synthesis of a new cobalt complex which contains BF₂⁺ bridges is achieved with the bis(E,E)-dioxime ligand. The trinuclear complex of this Co^III complex has been obtained by the reaction of BF₂⁺ bridged Co^III complex with Pd[bis(benzonitrile)]Cl₂. The structures of these complexes and (E,E)-dioxime were identified by using elemental analysis, ¹H and ¹³C-NMR, IR and MS spectral data.     

Anomalies in the molecular ion region in the electron impact mass spectra of α- and β-hydroxyesters

In the electron impact mass spectra of some alkyl α- and β-hydroxyesters (introduced using the gas chromatography/mass spectrometry (GC/MS) technique), the absence of the molecular ion M^+· and the presence of the [M + 1]⁺ ion instead is observed. This phenomenon is especially characteristic of C₃? C₆ glycolates and diethyl malate, and is due to chemical auto-ionization—ion-molecule reactions in the high concentration gradient at the top of the GC peak. The existence of the [M ? 2]^+·, [M ?1]⁺ and M^+· ions in the mass spectra of other β- and α-hydroxyesters is discussed.     

Glycosylidene Carbenes. Part 15. Synthesis of disaccharides from allopyranose-derived vicinal 1,2-diols. Evidence for the protonation by a H-bonded hydroxy group in the σ-plane of the intermediate carbene,followed by attack on the oxycarbenium ion in the π-plane

The α-D -allo-diol 9 possesses an intramolecular H-bond (HO? C(3) to O? C(1)) in solution and in the solid state (Fig. 2). In solution, it exists as a mixture of the tautomers 9a and 9b (Fig. 3), which possess a bifurcated H-bond, connecting HO? C(2) with both O? C(1) and O? C(3). In addition, 9a possesses the same intramolecular H-bond as in the solid state, while 9b is characterized by an intramolecular H-bond between HO? C(3) and O? C(4). In solution, the β-D -anomer 12 is also a mixture of tautomers, 12a and presumably a dimer. The H-bonding in 9 and 12 is evidenced by their IR and ¹H-NMR spectra and by a comparison with those of 3–8, 10 , and 11 . The expected regioselectivity of glycosidation of 9 and 12 by the diazirine 1 or the trichloroacetimidate 2 is discussed on the basis of the relative degree of acidity/nucleophilicity of individual OH groups, as governed by H-bonding. Additional factors determining the regioselectivity of glycosidation by 1 are the direction of carbene approach/proton transfer by H-bonded OH groups, and the stereoelectronic control of both the proton transfer to the alkoxy-alkyl carbene (in the σ-plane) and the combination of the thereby formed ions (π-plane of the oxycarbenium ion). Glycosidation of 9 by the diazirine 1 or the trichloroacetimidate 2 proceeded in good yields (75–94%) and with high regioselectivity. Glycosidation of 9 and 12 by 1 or 2 gave mixtures of the disaccharides 14–17 and 18–21 , respectively (Scheme 2). As expected, glycosidation of 12 by 1 or by 2 gave a nearly 1:1 mixture of regioisomers and a slight preference for the β-D -anomers (Table 4). Glycosidation of the α-D -anomer 9 gave mostly the 1,3-linked disaccharides 16 and 17 (α-D β-D ) along with the 1,2-linked disaccharides 14 and 15 (α-D < β-D , 1,2-/1,3-linked glycosides ca. 1:4), except in THF and at low temperature, where the β-D -configurated 1,2-linked disaccharide 15 is predominantly formed. Similarly, glycosidation of 9 with 2 yielded mainly the 1,3-linked disaccharides (1,2-/1,3-linked products ca. 1:3 and α-D /β-D ca. 1:4). Yields and selectivity depend upon the solvent and the temperature. The regioselectivity and the unexpected stereoselectivity of the glycosidation of 9 by 1 evidences the combined effect of the above mentioned factors, which also explain the lack of regio-complementarity in the glycosidation of 9 by 1 and by 2 (Scheme 3). THF solvates the intermediate oxycarbenium ion, as evidenced by the strong influence of this solvent on the regio- and stereoselectivity, particularly at low temperatures, where kinetic control leads to a stereoelectronically preferred axial attack of THF on the oxycarbenium ion.     

A mass spectral study of 1-(aryldimethylsilyl)-2-propanones and their isomeric 2-(aryldimethylsiloxy)-1-propenes

The mass spectra of a series of β-ketosilanes, p-Y? C₆H₄Me₂SiCH₂C(O)Me and their isomeric silyl enol ethers, p-Y? C₆H₄Me₂SiOC(CH₃)?CH₂, where Y = H, Me, MeO, Cl, F and CF₃, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]⁺, [M? C₆H₄Y·]⁺, [M? Me₂SiO]⁺˙, [M? C₃H₄]⁺˙, [M? HC?CCF₃]⁺˙, [Me₂SiOH]⁺˙ and [C₃H₆O]⁺˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me₂SiO]⁺˙ and [Me₂SiOH]⁺˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.     

Infrared Photodissociation Spectroscopic and Theoretical Study of the HC2nO+ (n=3-6) Cations

The carbon chain cations, HC_2nO⁺ (n=3-6) are produced via a pulsed laser vaporization supersonic expansion ion source in the gas phase. Their infrared spectra are measured via mass-selected infrared photodissociation spectroscopy of the CO “tagged” [HC_2nO·CO]⁺ cation complexes in 1600-3500 cm^-1 frequency range. The geometric and electronic structures of the [HC_2nO·CO]⁺ complexes and the core HC_2nO⁺ (n=3-6) cations are determined with the aid of density functional theory calculations. These HC_2nO⁺(n=3-6) ions are identified to be linear carbon chain derivatives terminally capped by hydrogen and oxygen. The triplet ground states are 10-15 kcal/mol lower in energy than the singlet states, indicating cumulene-like carbon chain structures.     

Complex Formation in Systems Cobalt(II)-Glycine-Beta-Lactam Antibiotics

Complex formation in solutions containing cations Co²⁺, glycine anions (Gly), and β-lactam antibiotics—ampicillin (Amp), amoxicillin (Axn), and cefalexin (Cpx)—has been investigated using pH-metric titration at 20°C and ionic force strength of 0.1 (KNO₃). In a weakly alkaline medium, mixed-ligand complexes [CoGlyAmp], [CoGlyAxn], and [CoGlyCpx], which are in equilibrium with [CoGly]⁺ complexes, are formed in the systems. The formation constants of complexes have been determined. The distribution diagrams of complex cobalt(II) species depending on pH have been constructed.     

Mass spectral behavior of n-alkynes

The 70 e V-electron impact mass spectra of the C₇–C₁₀ n-alkynes have been determined as well as the metastable ion spectra of the molecular ions and the [CS₂]⁺ and [N₂O]⁺ charge exchange mass spectra of the C₇-C₉ n-alkynes. The metastable ion mass spectra provide only a limited opportunity to distinguish between isomers; however, the 70-eV EI mass spectra of isomeric compounds permit a ready distinction between isomers. The [CS₂]⁺ charge exchange mass spectra of isomeric compounds also show substantial differences. The [N₂O]⁺ charge exchange mass spectra do not show the enhancement of β-fission fragments observed in field ionization experiments, despite representing ions of similar internal energy, and it is concluded that field dissociation is responsible for the β-fission fragments in the field ionization experiments.     

Precise analysis of thyroxine enantiomers in pharmaceutical formulation by mobility difference based on cyclodextrin

Identification and determination of chiral pharmaceutical residues is still a challenging analytical puzzle. In this work, a simple, rapid, and effective method for chiral D/L-tetraiodothyronine (T4) separation and quantitative was developed based on host–guest recognition using ion mobility spectrometry-mass spectrometry (IMS-MS). The D/L-T4 enantiomers were mobility separated by their diastereomeric complexes through mixing with cyclodextrin (CD) and metal ions. D/L-T4 was first separated by complexing with host molecule (α-, β-, γ-CD), observing weak peak-to-peak resolution (R_p-p) by the formed binary complex [CD + D/L-T4-H]⁺, and the R_p-p decreased with the CD size increasing. However, the separation effect of D/L-T4 was much improved with the addition of divalent metal ions (G²⁺) by the formed ternary complex [CD + D/L-T4 + G]²⁺. In comparison, α-CD related complexes can possess the best separation effect for D/L-T4 in most cases. Considering the high selectivity, non-toxic, and chemically stable of β-CD, [β-CD + D/L-T4 + Ca]²⁺ was selected for D/L-T4 analysis (R_P-P = 0.764). Whereafter, chemical theoretical conformations for [β-CD + D/L-T4 + H]⁺ and [β-CD + D/L-T4 + Ca]²⁺ were optimized, discovering similar micro-interaction modes between [β-CD + D-T4 + H]⁺ and [β-CD + L-T4 + H]⁺; while with the addition of Ca²⁺, significantly different interaction modes were observed between [β-CD + D-T4 + Ca]²⁺ and [β-CD + L-T4 + Ca]²⁺. And theoretical collision cross section (CCS) trends for the complexes were consistent with that of the experimental results. Additionally, calibration curves were linear within 1.00 to 10⁴ ng mL^?1 with coefficient (R² > 0.99), gaining the limit of detection (LODs) calculation of 0.11 ng mL^?1, and the detection range between D-T4 and L-T4 of 45.6:1 to 1:59.8. Finally, the method was applied for D/L-T4 detection in Levothyroxine tablets, the detection content has good consistency on drug labeling. Because the proposed method exhibited good analytical performance in terms of speed, selectivity, sensitivity, and reproducibility of the measurements, that can be a promising strategy for effective D/L-T4 detection in pharmaceutical industries or other practical samples.     

含N—取代乙二胺类配体的钴(Ⅲ)配合物的研究 Ⅰ.配合物[Co(acac)2L]+(L=N—甲基和苯基取代乙二胺类)的合成、稳定性及配体的配位场强度的研究

利用原料配合物[Co(acac)₃]和N-甲基和苯基取代乙二胺类配体在甲醇溶媒和活性炭的存在下进行反应,合成了一系列新的八面体型[Co(acac)₂L]⁺(L=N-甲基和笨其取代乙二胺类配体,acac=2,4-戊二酮离子)配合物。本文合成的七种配合物的分离和纯化都是采用以SP—SephadcxC 阳离子交换树脂为填充剂的柱型色谱技术进行的。所有配合物的紫外可见吸收光谱的第吸收带都在16600-18300cm^-1范围,表明¹A_1g→¹T_2g(O_h)的跃迁。并对N-甲基和苯基取代乙二胺配体的配位场强度进行了研究。     

Isothiocyanate and selenocyanate complexes of Cu(II), Ni(II), and Co(II) with a pyridylpyrazole-based ligand: synthesis,characterization, and structure

Mononuclear NCS^? containing complexes, [M(NCS)₂L] (L?=?N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine), [Cu(NCS)₂L′] (L′?=?N-(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine), and NCSe^? containing complexes [ML(NCSe)(H₂O)]ClO₄ (M?=?Ni⁺², Co⁺²) have been synthesized and characterized by elemental analysis, spectroscopic, and physico-chemical methods. Structural studies of [Cu(NCS)₂L′] show copper is five coordinate with distorted trigonal bipyramidal geometry with two cis NCS^?. [M(NCS)₂L] and [ML(NCSe)(H₂O)]ClO₄ (M?=?Ni⁺² and Co⁺²) are expected to be octahedral.     

Structural models of vanadate-dependent haloperoxidases and their reactivity

Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent haloperoxidases have been reported. On reaction with [VO(acac)₂] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to give oxovanadium(V), dioxovanadium (V) or μ-oxobisoxovanadium(V) species depending upon the nature of the ligand. Anionic and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The anionic complexes [VO₂(ONO)]^- can also be convertedin situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]⁺ and to peroxo complexes [VO(O₂)(ONO)]^-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol (H₂cat) and benzohydroxamic acid (H₂bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)] respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO₂(ONN)] as observed by⁵¹V NMR and electronic absorption spectroscopic studies.