Reactivity of Cationic Terminal Borylene Complexes: Novel Mechanisms for Insertion and Metathesis Chemistry Involving Strongly Lewis Acidic Ligand Systems

The reactions of terminal borylene complexes of the type [CpFe(CO)(2)(BNR2)](+) (R = `Pr, Cy) with heteroallenes have been investigated by quantum-chemical methods, in an attempt to explain the experimentally observed product distributions. Reaction with dicyclohexylcarbodiimide (CyNCNCy) gives a bis-insertion product, in which 1 equiv of carbodiimide is assimilated into each of the Fe=B and B=N double bonds to form a spirocyclic boronium system. In contrast, isocyanates (R'NCO, R' = Ph, 2,6-wXy1, CY; XYl = C6H3Me2) react to give isonitrile complexes of the type [CpFe(CO)(2)(CNR')]+, via a net oxygen abstraction (or formal metathesis) process. Both carbodiimide and socyanate substrates are shown to prefer initial attack at the Fe=B bond rather than the B=N bond of the borylene complex. Further mechanistic studies reveal that the carbodiimide reaction ultimately leads to the bis-insertion compounds [CpFe(CO)(2)C(NCy)(2)B(NCY)(2)CNR2](+), rather than to the isonitrile system [CpFe(CO)(2)(CNCy)](+), on the basis of both thermodynamic (product stability) and kinetic considerations (barrier heights). The mechanism of the initial carbodiimide insertion process is unusual in that it involves coordination of the substrate at the (borylene) ligand followed by migration of the metal fragment, rather than a more conventional process: i.e., coordination of the unsaturated substrate at the metal followed by ligand migration. In the case of isocyanate substrates, metathesis products are competitive with those from the insertion pathway. Direct, single-step metathesis reactivity to give products containing a coordinated isonitrile ligand (i.e. [CpFe(CO)(2)(CNR')](+)) is facile if initial coordination of the isocyanate at boron occurs via the oxygen donor (which is kinetically favored); insertion chemistry is feasible when the isocyanate attacks initially via the nitrogen atom. However, even in the latter case, further reaction of the monoinsertion product so formed with excess isocyanate offers a number of facile (low energetic barrier) routes which also generate ['CpFe(CO)(2)(CNR')](+), rather than the bis-insertion product [CpFe(CO)(2)C(NR')(O)B(NR')(O)CNR2](+) (i.e., the direct analogue of the observed products in the carbodiimide reaction).

X-ray Studies on Crystalline Complexes Involving Amino Acids and Peptides. XIII. Effect of Chirality on Molecular Aggregation: The Crystal Structures of L-Arginine D-Aspartate and L-Arginine D-Glutamate Trihydrate

The crystal structures of (1) L-arginine D-asparate, C6HIsN40~.C4H6NO4 [triclinic, P1, a=5.239(1), b=9.544(1), c=14.064(2)A, a=85"58(1), /3=88.73 (1), ~/=84.35 (1) °, Z=2] and (2) L-arginine D-glutamate trihydrate, C6H15N40~-.CsHsNO4.3H20 [monoclinic, P2~, a=9.968(2), b=4.652(1), c=19.930 (2) A, fl = 101.20 (1) °, Z = 2] have been determined using direct methods. They have been refined to R =0.042 and 0.048 for 2829 and 2035 unique reflections respectively [I>2cr(I)]. The conformations of the two arginine molecules in the aspartate complex are different from those observed so far in the crystal structures of arginine, its salts and complexes. In both complexes, the molecules are organized into double layers stacked along the longest axis. The core of each double layer consists of two parallel sheets made up of main-chain atoms, each involving both types of molecules. The hydrogen bonds within each sheet and those that interconnect the two sheets give rise to EL-, DD- and DE-type head-to-tail sequences. Adjacent double layers in (1) are held together by side-chain-side-chain interactions whereas those in (2) are interconnected through an extensive network of water molecules which interact with sidechain guanidyl and carboxylate groups. The aggregation pattern observed in the two LD complexes is fundamentally different from that found in the corresponding EL complexes.

Complexes Of Imidazoline-2-Thione And Its 1-Methyl Analogue With Cu(Ii), Zn(Ii), Cd(Ii) And Hg(Ii) Salts

The reaction of Cu(II), Zn(II), Cd(II) and Hg(II) chlorides and bromides with imidazoline-2-thione (IZT) and its N-methyl derivative (NMIZT) yields complexes of stoichiometry ML3X2 and ML2X (IZT) and its N-methyl derivative (NMIZT) yields complexes of stoichiometry ML3X2 and ML2X (where M=Cu(I)); copper(II) halides yield Cu(I) complexes. On the basis of infrared and 13C n.m.r.

Metal Chelates in Vinyl Polymerization: Kinetics and Mechanism of Acrylonitrile Polymerization Initiated by Cu(I1) Imine Complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(I1) 4-anilino 3-pentene 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(I1) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCld), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 22 at two different temperatures and in different solvents. The square-root dependence of R, on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formatign was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

13c And 1h Nmr Study Of Complexes Of 2-Pyridinethione And 4-Pyridinethione With Zn(Ii), Cd(Ii) And Hg(Ii) Halides

Proton and carbon-13 NMR has been used to study complexes of 2-pyridinethione (in its basic and deprotonated forms) and 4-pyridinethione with zinc(II), cadmium(II) and mercury(II) halides. The variations in the carbon-13 and proton chemical shifts are discussed.

Raman Spectroscopic study of valinomycin-metal complexes

Valinomycin, an ionophore of considerable interest for its ion selectivity, and its K+, Mg2+, Ba2+, and Ca2+ complexes were studied by Raman spectroscopy. Each complex has a characteristic spectrum which differs from that of uncomplexed valinomycin, suggesting several distinct structures for each of the metal-valinomycin complexes. The biologically active potassium complex shows the most significant changes in its spectrum, especially in the intensity of the symmetric C---H stretching vibration of CH3 and the convergence of the two ester carbonyl stretching vibration bands into one complex formation. These results are due to the unique orientation of the ester carbonyl groups toward the caged potassium ion and the resulting more free rotation of isopropyl side chains. The divalent cation-valinomycin complexes examined showed spectra which differed in each case uniquely from both valinomycin and its complex with potassium.

An infrared spectroscopic study of the phase transitions of crystalline aromatic donor-acceptor complexes involving a pseudoplastic state

Variable temperature i.r. spectroscopic studies of weak pi-donor-pi-acceptor complexes in the crystalline state indicate that the complexes undergo order-disorder transitions, the disorder being caused by molecular motion. Thermodynamic data on the phase transitions along with the spectral data suggest that the high-temperature crystalline forms of the complexes are likely to be pseudoplastic.

Structure and properties of two component hydrogels comprising lithocholic acid and organic amines

We demonstrate the aptitude of supramolecular hydrogel formation using simple bile acid such as lithocholic acid in aqueous solution in the presence of various dimeric or oligomeric amines. By variation of the choice of the amines in such mixtures the gelation properties could be modulated. However, the replacement of lithocholic acid (LCA) by cholic acid or deoxycholic acid resulted in no hydrogel formation. FT-IR studies confirm that the carboxylate and ammonium residues of the two components are involved in the salt (ion-pair) formation. This promotes further assembly of the components reinforced by a continuous hydrogen bonded network leading to gelation. Electron microscopy shows the morphology of the internal organization of gels of two component systems which also depends significantly on the amine part. Variation of the amine component from the simple 1,2-ethanediamine (EDA) to oligomeric amines in such gels of lithocholic acid changes the morphology of the assembly from long one-dimensional nanotubes to three-dimensional complex structures. Single crystal X-ray diffraction analysis with one of the amine-LCA complexes suggested the motif of fiber formation where the amines interact with the carboxylate and hydroxyl moieties through electrostatic forces and hydrogen bonding. From small angle neutron scattering study, it becomes clear that the weak gel from LCA-EDA shows scattering oscillation due to the presence of non-interacting nanotubules while for gels of LCA with oligomeric amines the individual fibers come together to form complex three-dimensional organizations of higher length scale. The rheological properties of this class of two component system provide clear evidence that the flow behavior can be modulated varying the acid-amine ratio.

Photo-induced double-strand DNA and site-specific protein cleavage activity of L-histidine (mu-oxo)diiron(III) complexes of heterocyclic bases

Three oxo-bridged diiron(III) complexes of L-histidine and heterocyclic bases [Fe-2(mu-O)(L-his)(2)(B)(2)](ClO4)(2) (1-3), where B is 2,2'-bipyridine (bpy),1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), were prepared and characterized. The bpy complex 1 was structurally characterized by X-ray crystallography. The molecular structure showed a {Fe-2(mu-O)} core in which iron(III) in a FeN4O2 coordination is bound to tridentate monoanionic L-histidine and bidentate bpy ligands. The Fe center dot center dot center dot Fe distance is similar to 3.5 angstrom. The Fe-O-Fe unit is essentially linear, giving a bond angle of similar to 172 degrees. The complexes showed irreversible cyclic voltammetric cathodic response near -0.1 V vs. SCE in H2O-0.1 M KCl. The binuclear units displayed antiferromagnetic interaction between two high-spin (S = 5/2) iron(III) centers giving a -J value of -110 cm(-1). The complexes showed good DNA binding propensity giving a binding constant value of similar to 10(5) M-1. Isothermal titration calorimetric data indicated single binding mode to the DNA. The binding was found to be driven by negative free energy change and enthalpy. The dpq complex 3 showed oxidative double-strand DNA cleavage on exposure to UV-A and visible light. The phen complex 2 displayed single-strand photocleavage of DNA. The DNA double-strand breaks were rationalized from theoretical molecular docking calculations. Mechanistic investigations showed formation of hydroxyl radicals as the reactive species through photodecarboxylation of the L-histidine ligand. The complexes exhibited good binding propensity to bovine serum albumin (BSA) protein in Tris-HCl/NaCl buffer medium. The dpq complex 3 showed UV-A light-induced site-specific oxidative BSA cleavage forming fragments of similar to 45 kDa and similar to 20 kDa molecular weights via SOH pathway.

X-ray studies on crystalline complexes involving amino acids and peptides. Part XIV: Closed conformation and head-to-tail arrangement in a new crystal form of L-histidine L-aspartate monohydrate

A new form of L-histidine L-aspartate monohydrate crystallizes in space group P22 witha = 5.131(1),b = 6.881(1),c= 18.277(2) Å,β= 97.26(1)° and Z = 2. The structure has been solved by the direct methods and refined to anR value of 0.044 for 1377 observed reflections. Both the amino acid molecules in the complex assume the energetically least favourable allowed conformation with the side chains staggered between the α-amino and α-scarboxylate groups. This results in characteristic distortions in some bond angles. The unlike molecules aggregate into alternating double layers with water molecules sandwiched between the two layers in the aspartate double layer. The molecules in each layer are arranged in a head-to-tail fashion. The aggregation pattern in the complex is fundamentally similar to that in other binary complexes involving commonly occurring L amino acids, although the molecules aggregate into single layers in them. The distribution of crystallographic (and local) symmetry elements in the old form of the complex is very different from that in the new form. So is the conformation of half the histidine molecules. Yet, the basic features of molecular aggregation, particularly the nature and the orientation of head-to-tail sequences, remain the same in both the forms. This supports the thesis that the characteristic aggregation patterns observed in crystal structures represent an intrinsic property of amino acid aggregation.

An ultraviolet photoelectron spectroscopic study of the electron states of iodine complexes with electron donors

HeI photoelectron spectra of the vapour phase complexes of diethylether and diethylsulphide with iodine have been investigated for the first time. The iodine orbital ionization energy decreases on complexation while the donor lone-pair orbital ionization energy increases markedly; the shifts are considerably larger in the sulphide complex as expected on the basis of enthalpy considerations.

Interaction of manganese(II) with valinomycin: Observation of mixed complexes

The interaction of antibiotic valinomycin with manganese (II) has been studied using circular dichroism, electron spin resonance and infrared techniques. Results show that Mn(II) forms complexes with valinomycin in both 2:1 (valinomycin-ion-valinomycin sandwich) and 1:1 (equimolar) stoichiometries. The 1:1 type observed here is very different from the well known K+-valinomycin bracelet conformation.

Complexes of lanthanide perchlorates with two new O,N,O ligands derived from antipyraldehyde and acetic and benzoic acid hydrazides

Antipyrine is a well known ligand for lanthanides (I). A forage through the organic literature of pyrazolones reveals that the 4-position of antipyrine is amenable to a wide variety of organic reactions. It should thus be possible to introduce suitable functional groups at this position and design new multidentate ligands for metal ions. It is also found that the coordination chemistry of lanthanides is much less well developed and far fewer ligands have been used for complexation with lanthanide ions compared to that of the d-transition metal ions. Keeping these points in view we have reported earlier, complexes of lanthanides with a bidentate ligand N,N-diethyl-antipyrine-4-carboxamide (2). In this communication we report the synthesis of two new ligands from Schiff base condensation of antipyraldehyde and the hydrazides of acetic and benzoic acids and the complexes formed by these hydrazones with lanthanide perchlorates.

Synthesis and Characterisation of Metal Hydrazine Nitrate, Azide and Perchlorate Complexes

Metal hydrazine nitrate complexes of the type M(N2H4)Nn (NO3)2 where M = Mg, n = 2; M = Mn, Fe, Co, Ni, Zn and Cd and n = 3; metal dihydrazine azide complexes of the type M(N2H4)2 (N3)2 where M = Mg, Co, Ni and Zn; and Mg(N2H4)2 (C1O4)2 have been prepared by dissolving the respective metal powders in the solution of corresponding ammonium salts (NO3, N3 and C1O4) in hydrazine hydrate. These hydrazine complexes were also prepared by the conventional method involving the addition of alcoholic hydrazine hydrate to the aqueous solution of metal salts. The hydrazine complexes have been characterised by chemical analysis, infrared spectra and differential thermal analysis (DTA). Impact sensitivities of hydrazine complexes were determined by the drop weight method. The reactivity of these hydrazine complexes does not change with the method of preparation.