Spectroscopic study of the interaction of poly(ε-N-methacryloyl-L-lysine) with copper(II)

The complexes formed between copper(II) and a polymeric ligand derived from L -lysine, poly(ε-N-methacryloyl-L -lysine) have been investigated by electronic absorption, circular dichroïsm, and EPR spectroscopy. The model molecule, ε-N-isobutyroyl-L -lysine was also studied with the purpose to distinguish between the effects due to the polymeric nature of the ligand and its intrinsic complexing properties. All experiment results are consistent with the existence of two CuL and CuL₂ complexes for both model and polymer Cu systems with no deprotonation of the amide group. The two complexes involve only the carboxyl and amino groups. With the polymer, the CuL₂ complex is the main species, even at low pH and low [ligand]/[metal] ratio. This is attributed to the high local concentration of ligand in the vicinity of the polymer chain. With the model molecule, on the contrary, the distribution of the two complexes is strongly dependent on the pH and the [ligand]/[metal] ratio.     

Tris(ethyl­ene­diamine)­nickel(II) bis­[2‐cyano‐2‐(oxidoimino)­acetamidato]­nickelate(II) monohydrate

The title compound, [Ni(C₂H₈N₂)₃][Ni(C₃HN₃O₂)₂]·H₂O, appears to be a modular associate consisting of two complex counter‐ions, containing bivalent nickel as the central atom in both cases, and a solvent water mol­ecule. The Ni^II ion in the complex cation lies on the C₂ crystallographic axis. Its coordination environment is formed by six N atoms of three ethyl­ene­diamine (en) mol­ecules, representing a distorted octa­hedral geometry. The Ni^II ion in the complex anion occupies a position at the center of inversion. It exhibits a distorted square‐planar coordination geometry formed by four N atoms belonging to the deprotonated oxidoimine and amide groups of the two doubly charged 2‐cyano‐2‐(oxidoimino)acetamidate anions, situated in trans positions with respect to each other. In the crystal packing, the complex anions are linked by water mol­ecules via hydrogen bonds between the amide O atoms and water H atoms, forming chains translated along the a direction. The [Ni(en)₃]²⁺ cations fill empty spaces between the translational chains, connecting them by hydrogen bonds between the oxime and amide O atoms of the anions and the amine H atoms of the cations, forming layers along the ac plane. The water mol­ecules provide connection between layers through N atoms of the cations, thus forming a three‐dimensional modular structure.     

Hydrolysis of amide bond in histidine-containing peptides promoted by chelated amino acid palladium(II) complexes: dependence of hydrolytic pathway on the coordination modes of the peptides

Hydrolytic reactions between cis-[Pd( -Ala-N,O)Cl₂]⁻ and cis-[Pd( -Ala-N,O)(H₂O)₂]⁺, in which -Ala is alanine coordinated through N and O atoms, and N-acetylated peptides -histidylglycine (MeCO-His-Gly), glycyl- -histidine (MeCO-Gly-His), glycylglycyl- -histidine (MeCO-Gly-Gly-His) and glycyl- -histidylglycine (MeCO-Gly-His-Gly) were studied by ¹H NMR spectroscopy. All reactions were carried out in the pH range 2.0–2.5 and two different temperatures, 22 and 60°C. In the reactions of these two palladium(II) complexes with MeCO-His-Gly, complete hydrolysis of the amide bond involving carboxylic group of histidine occurs in less than 24 h. The cleavage is regioselective. With peptides containing free a carboxylic group of histidine, MeCO-Gly-His and MeCO-Gly-Gly-His, palladium(II) complex promote the cleavage of the MeCO–Gly and Gly–Gly amide bonds. No cleavage of the Gly–His amide bond was observed. The mechanism of these hydrolytic reactions involves release of -Ala ligand and aquation of the palladium(II) complex chelated to the substrate through the imidazole N-3 atom and deprotonated nitrogen atom of the amide bond involving amino group of histidine. This aqua complex represents a catalytically active form different from the initially added catalytically inactive complex. In the reactions of palladium(II) complexes with tripeptide MeCO-Gly-His-Gly, two amide bonds, MeCO–Gly and His–Gly, were cleaved. The mechanism of the cleavage of these amide bonds is correlated with two different palladium(II)–substrate catalytically active forms. These findings contribute to the better understanding of selective cleavage of peptides and proteins and must be taken into consideration in designing new reagents for this purpose.     

Synthesis and structures of some diorganotin bis(hydroxamate)s

Analysis of literature data on the antitumor activity of organotin compounds reveals that R₂SnX₂ and their complexes containing Sn? O, Sn? N or Sn? S bonds often exhibit biological activity, especially if such bonds are formed by means of intramolecular coordination. Furthermore, a wide range of biological activities, from fungicidal, bactericidal and antiseptic to psychotropic and antitumor, is found to be characteristic for some organic hydroxamic acids (N-acylhydroxylamines). From this point of view the diorgantion bis-hydroxamates in this paper are of particular interest as potential biologically active antitumor drugs. Di-n-butyltin bis(N-methyl-N-p-bromobenzoylhydroxylamine) is being screened for antitumor activity.     

Asymmetric anionic polymerization of (2-fluorophenyl)(4-fluorophenyl)(2-pyridyl)methyl methacrylate leading to a helical polymer

A novel racemic methacrylate, (2-fluorophenyl)(4-fluorophenyl)(2-pyridyl)-methyl methacrylate¹ (2F4F2PyMA), was synthesized and polymerized with chiral complexes of N,N′-diphenylethylenediamine monolithium amide (DPEDA-Li) with (−)-sparteine (Sp), (2S, 3S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane (DDB), and (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine (PMP) in toluene at −78°C. The monomer showed higher resistance against methanolysis compared with triphenylmethyl methacrylate (TrMA) and several other analogues. In the asymmetric anionic polymerization of 2F4F2PyMA, PMP was found to be a more effective chiral ligand than DDB and Sp and gave quantitatively an optically active polymer with nearly perfect isotacticity. Enantiomer selection was observed in the polymerization of racemic 2F4F2PyMA with the chiral lithium complexes. Chiral recognition ability of the optically active poly(2F4F2PyMA) was examined by an enantioselective adsorption experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2013–2019, 1998     

Backbone Reactivity of Lithium β-Diketiminate (NacNac) Complexes with CO2, tBuNCO and iPrNCO

Though alkali metal NacNac (β-diketiminate) complexes have been utilised in synthesis as NacNac-transfer agents, studies of them in their own right with small molecules are exceptionally rare. Here, the lithium compound of the common 2,6-diisopropylphenyl-β-methyldiketiminate [NacNac(Dipp, Me)] ligand is investigated with carbon dioxide and isocyanates. In all four cases reaction occurs at the backbone γ-C atom of the NacNac ligand, which redistributes electronically into a diimine. Insertion of CO₂ gives an eight-atom carboxylate (Li₂O₄C₂) ring at the γ-C site in a dimer. Insertion of tBuNCO gives a secondary amide at the γ-C site in a monomer with TMEDA chelating lithium. Double insertion of tBuNCO and (adventitious) oxygen gives a dimer with a (LiO)₂ central core involving the latter source. Insertion of less bulky (iPrNCO) gives a dimer with dimerisation through the C=O bonds of the emergent secondary amide function.     

Synthesis of poly(vinylamine) containing asymmetric nucleic acid base derivatives as grafted pendants

The preparations of new model polymers of polynucleotides with stereoregular poly(vinylamine) (PVAm) backbones and an optically active nucleic acid base derivative as a pending side chain are described. The grafting of (±)-, (+)-, and (?)-2-(thymin-1-yl) propionic acid to linear PVAm prepared either by hydrolysis of poly(vinyl acetamide) or poly(vinyl-t-butyl carbamate) has proven to be more difficult than the case of polyethyleneimine. This may be due to a combination of the low solubility and steric factors of PVAm. PVAm formed a complex with oximes such as ethyl-2-hydroxyimino cyanoacetate (EHICA), which activates the amino group of PVAm; it became soluble in polar solvents and gave higher percent graft. These carboxylic acid derivatives were grafted onto PVAm through amide bonds by direct coupling with sulfonic acid esters of hydroxybenzotriazoles to give optically active graft polymers. These coupling agents were found to be much superior reagents than DEPC regarding racemization. The related monomer and dimer model compounds were also prepared by the same method from 3-aminopentane and (?)-, (+)-, and meso-2,4-diaminopentane, respectively. The dimer models were separated and purified by HPLC to give models for isotactic, heterotactic, and syndiotactic polymer models. The enantiomeric purity of the optically active monomer model was determined by 360-MHz NMR spectroscopy using optically active shift reagents.     

Temperature-induced phase transition of poly(N,N-dimethylaminoethyl methacrylate-co-acrylamide)

Copolymers of N,N-dimethylaminoethyl methacrylate (DMAEMA) and acrylamide (AAm) were prepared to demonstrate a temperature-induced phase transition. Poly DMAEMA has a lower critical solution temperature (LCST) around 50°C in water. With copolymerization of DMAEMA with AAm, the LCST shifts to the lower temperature was observed, probably due to the formation of hydrogen bonds between amide and N,N-dimethylamino groups. FT-IR studies clearly show the formation of hydrogen bonds which protect N,N-dimethylamino groups from exposure to water and result in a hydrophobic contribution to the LCST. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 595–598, 1997     

Bis[1,1‐di­methyl­biguanide(1–)‐κ2N2,N5]copper(II) monohydrate

The crystal structure of the title compound, [Cu(C₄H₁₀N₅)₂]·H₂O, contains two independent copper N,N‐di­methyl­biguanide complex units, each with square‐planar coordination of the Cu atom by four N atoms. The two complexes have different symmetry, with one Cu atom lying on an inversion centre and the other on a twofold rotation axis. The Cu—N bond lengths are 1.923 (2) and 1.950 (2) Å in the centrosymmetric complex, and 1.928 (2) and 1.938 (2) Å in the non‐centrosymmetric complex. The crystal structure is stabilized by N—H⋯O, O—H⋯N and N—H⋯N hydrogen bonds; each water mol­ecule forms four hydrogen bonds involving three different Cu complexes.     

Coordination properties of Cu(II) and Ni(II) ions towards the C-terminal peptide fragment -TYTEHA- of histone H4

In order to reveal more information about the toxicity caused by metals and furthermore their influence to the physiological metabolism of the cell, the hexapeptide model Ac-ThrTyrThrGluHisAla-am representing the C-terminal 71-76 fragment of histone H4 which lies into the nucleosome core, was synthesized. A combined pH-metric and spectroscopic UV-VIS, EPR, CD and NMR study of Ni(II) and Cu(II) binding to the blocked hexapeptide, revealed the formation of octahedral complexes involving imidazole nitrogen of histidine, at pH 5 and pH 7 for Cu(II) and Ni(II) ions respectively. In basic solutions a major square-planar 4 N Ni(II)-complex, adopting a {N(Im), 3N(-)} coordination mode, was formed. In the case of Cu(II) ions, a 3 N complex, involving the imidazole nitrogen of histidine and two deprotonated amide nitrogens of the backbone of the peptide, at pH 7 and a series of 4 N complexes starting at pH 6.5, were suggested. In addition Ni(II)-mediated hydrolysis of the peptide bond-Tyr-Thr was evident following our experimental data.     

Reactions of Nitridotechnetium(V) Complexes with Boranes

Nitrido bridges between technetium and boron were formed during reactions of [TcN(PMe₂Ph)(Et₂dtc)₂] (Et₂dtc^? = diethyldithiocarbamate) and BH₃ or BPhCl₂ at low temperatures. X‐Ray structure determinations show that the products contain almost linear Tc–N–B bonds with Tc–N distances which are only slightly lengthened with respect to the triple bonds in the precursor molecule. However, a significant lengthening of the Tc–S bond trans to the nitrido ligand is detected by the decrease of the structural trans influence of “N^3?”N. The compounds are instable and decompose at room temperature under cleavage of the N–B bonds. A reaction between [TcNCl₂(PPh₃)₂] and BCl₃ does not yield a product with a nitrido bridge. Prolonged heating in dichloromethane results in decomposition of the technetium complex and the formation of (HPPh₃)₂[TcCl₆]. Hydrogen bonds are established between the complex anion and each two counter ions.     

Interaction of N-(aryl)picolinamides with iridium. N–H and C–H bond activations

Reaction of N-(4-R-phenyl)picolinamide (R = OCH₃, CH₃, H, Cl and NO₂) with [Ir(PPh₃)₃Cl] in refluxing ethanol in the presence of a base (NEt₃) affords two yellow complexes (1-R and 2-R). The 1-R complexes contain an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphines, a chloride and a hydride. The 2-R complexes contain an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphines and two hydrides. Similar reaction of N-(naphthyl)picolinamide with [Ir(PPh₃)₃Cl] affords two organometallic complexes, 3 and 4. In complex 3 the amide ligand is coordinated to the metal center, via C–H activation of the naphthyl ring at the 8-position, as a dianionic tridentate N,N,C donor, along with two triphenylphosphines and one chloride. Complex 4 is similar to complex 3, except a hydride is bonded to iridium instead of the chloride. Structures of the 1-OCH₃, 2-Cl and 4 complexes have been determined by X-ray crystallography. All the complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ir^III–Ir^IV oxidation within 0.50–1.16 V vs. SCE and a reduction of the coordinated amide ligand within −1.02 to −1.25 V vs. SCE.     

catena‐Poly[[dicyanamido(5,5′‐dimethyl‐2,2′‐bipyridine‐κ2N,N′)copper(II)]‐μ‐dicyanamido‐κ2N1:N5]

In the crystal structure of the title compound, [Cu(C₂N₃)₂(C₁₂H₁₂N₂)]_n, the Cu^II atom adopts a distorted square‐pyramidal geometry, the basal plane of which is formed by two N atoms of the bi­pyridine ligand, one N atom of a bidentate dicyan­amide anion and one N atom of a monodentate dicyan­amide anion [Cu—N = 1.9760 (15)–2.0157 (15) Å]. The apical position is occupied by an N atom of a bidentate dicyan­amide anion, located 2.2468 (16) Å from the Cu atom, thus forming a one‐dimensional polymeric chain.     

Ring-opening polymerization of coordination complexes: silver(I) complexes with bis(amidopyridine) ligands derived from thiophene

The thiophene-based bis(N-methylamido-pyridine) ligand SC4H2-2,5-{C(=O)N(Me)-4-C5H4N}2 reacts with silver(I) salts AgX to give 1 : 1 complexes, which are characterized in the solid state as the macrocyclic complexes [Ag(2){SC4H2-2,5-(CONMe-4-C5H4N)2}2][X]2, which have the cis conformation of the C(=O)N(Me) group, when X = CF3CO2, NO3, or CF3SO3 but as the polymeric complex [Ag(n){SC4H2-2,5-(CONMe-4-C5H4N)2}n][X]n, with the unusual trans conformation of the C(=O)N(Me) group, when X = PF6. The bis(amido-pyridine) ligand SC4H2-2,5-{C(=O)NHCH2-3-C5H4N}2 reacts with silver(I) trifluoroacetate to give the polymeric complex [Ag(n){SC4H2-2,5-(CONHCH2-3-C5H4N)2}n][X]n, X = CF3CO2. The macrocyclic complexes contain transannular argentophilic secondary bonds. The polymers self assemble into sheet structures through interchain C=O...Ag and S...Ag bonds in [Ag(n){SC4H2-2,5-(CONMe-4-C5H4N)2}n][PF6]n and through Ag...Ag, C=O...Ag and Ag...O(trifluoroacetate)...HN secondary bonds in [Ag(n){SC4H2-2,5-(CONHCH2-3-C5H4N)2}n][CF3CO2]n.     

Metal complexes of some asymmetric diaminodiamide ligands—II. Stabilities of complexes of nickel(II) in aqueous solution

Equilibria between a series of asymmetric diaminodiamides and Ni(II) in aqueous solution have been studied by potentiometric and spectrophotometric methods. The ligands were S,R,S- and S,S,S-N,N′-dialanylpropylenediamine (DAPN), S,S-N,N′-dialanylethylenediamine (DAEN), R-N,N′-diglycylpropylenediamine (DGPN), and N,N′-diglycylethylenediamine (DGEN). At lower values of pH the complexes NiL²⁺ and in some cases NiL²⁺₂ were formed. Spectral data indicated that both of these were octahedral. At higher pH the two amide protons were lost and square planar complexes were formed. The diastereomeric DAPN ligands showed stereoselectivity in the equilibrium constants for deprotonation and formation of the square planar complexes. Comparison of optical rotatory dispersion curves and absorption spectra for the various complexes permits partial assignment of structures.     

Low‐dimensional compounds containing cyano groups. X. (Dicyan­amido‐κN1)­bis(1,10‐phenanthroline‐κ2N,N′)copper(II) perchlorate

The title compound, [Cu(C₂N₃)(C₁₂H₈N₂)₂]ClO₄, represents a relatively rare class of compounds with dicyan­amide coordinated in a monodentate manner. The structure is formed by the [Cu{N(CN)₂}(phen)₂]⁺ complex cation (phen is 1,10‐phenanthroline) and an uncoordinated ClO₄⁻ anion. The Cu atom is five‐coordinate, with a slightly distorted trigonal–bipyramidal environment. The dicyan­amide ligand is coordinated through one nitrile N atom in the equatorial plane, at a distance of 2.033 (6) Å from the metal. The two axial Cu—N distances are similar [mean 1.999 (4) Å] and are substantially shorter than the remaining two equatorial Cu—N bonds [mean 2.087 (1) Å].     

Thermodynamic, kinetic and solid-state study of divalent metal complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) bearing two trans (1,8-)methylphosphonic acid pendant arms

Divalent metal complexes of macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane-1,8-bis(methylphosphonic acid)) (1,8-H4te2p, H4L) were investigated in solution and in the solid state. The majority of transition-metal ions form thermodynamically very stable complexes as a consequence of high affinity for the nitrogen atoms of the ring. On the other hand, complexes with Mn2+, Pb2+ and alkaline earth ions interacting mainly with phosphonate oxygen atoms are much weaker than those of transition-metal ions and are formed only at higher pH. The same tendency is seen in the solid state. Zinc(II) ion in the octahedral trans-O,O-[Zn(H2L)] complex is fully encapsulated within the macrocycle (N4O2 coordination mode with protonated phosphonate oxygen atoms). The polymeric {[Pb(H2L)(H2O)2].6H2O}n complex has double-protonated secondary amino groups and the central atom is bound only to the phosphonate oxygen atoms. The phosphonate moieties bridge lead atoms creating a 3D-polymeric network. The [{(H2O)5Mn}2(micro-H2L)](H2L).21H2O complex contains two pentaaquamanganese(II) moieties bridged by a ligand molecule protonated on two nitrogen atoms. In the complex cation, oxygen atoms of the phosphonate groups on the opposite sites of the ring occupy one coordination site of each metal ion. The second ligand molecule is diprotonated and balances the positive charge of the complex cation. Complexation of zinc(II) and cadmium(II) by the ligand shows large differences in reactivity of differently protonated ligand species similarly to other cyclam-like complexes. Acid-assisted dissociations of metal(II) complexes occur predominantly through triprotonated species [M(H3L)]+ and take place at pH < 5 (Zn2+) and pH < 6 (Cd2+).     

Synthesis and photochemical properties of poly(ester–amide)s containing norbornadiene (NBD) residues

N,N′‐Bis[(3‐carboxynorbornadien‐2‐yl)carbonyl]‐N,N′‐diphenylethylenediamine (BNPE) was synthesized in 70% yield by the reaction of 2,5‐norbornadiene‐2,3‐dicarboxylic acid anhydride with N,N′‐diphenylethylenediamine. Other dicarboxylic acid derivatives containing norbornadiene (NBD) residues having N,N′‐disubstituted amide groups were also prepared by the reaction of 2,5‐NBD‐2,3‐dicarboxylic acid anhydride with certain secondary diamines. When the polyaddition of BNPE with bisphenol A diglycidyl ether (BPGE) was carried out using tetrabutylammonium bromide as a catalyst in N‐methyl‐2‐pyrrolidone at 100°C for 12 h, a polymer with number average molecular weight of 69,800 was obtained in 98% yield. Polyadditions of other NBD dicarboxylic acid derivatives containing N,N′‐disubstituted amide groups with BPGE were also performed under the same conditions. The reaction proceeded very smoothly to give the corresponding NBD poly(ester–amide)s in good yields. Photochemical reactions of the obtained polymers with N,N′‐disubstituted amide groups on the NBD residue were examined, and it was found that these polymers were effectively sensitized by adding appropriate photosensitizers such as 4‐(N,N‐dimethylamino)benzophenone and 4,4′‐bis(N,N‐diethylamino)benzophenone in the film state. The stored energies in the quadricyclane groups of the polymers were also evaluated to be about 94 kJ/mol by DSC measurement of the irradiated polymer films. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 917–926, 1999     

Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes

The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions.     

Preparation of novel axially chiral NHC–Pd(II) complexes and their application in oxidative kinetic resolution of secondary alcohols

Novel axially chiral N‐heterocyclic carbene (NHC) Pd(II) complexes were prepared from optically active 1,1′‐binaphthalenyl‐2,2′‐diamine (BINAM) and H₈‐BINAM and their crystal structures were unambiguously determined by X‐ray diffraction. These chiral N‐heterocyclic carbene (NHC) Pd(II) complexes were applied in the oxidative kinetic resolution of secondary alcohols using molecular oxygen as a terminal oxidant or under aerobic conditions, affording the corresponding sec‐alcohols in good yields with moderate to good enantioselectivities. Copyright © 2009 John Wiley & Sons, Ltd.