Metal Complexes of Macrocyclic Schiff-Base Ligand: Preparation, Characterisation, and Biological Activity

A new macrocyclic multidentate Schiff-base ligand Na4L consisting of two submacrocyclic units (10,21-bis-iminomethyl-3,6,14,17-tricyclo[17.3.1.18,12]tetracosa-1(23),2,6,8,10,12(24),13,17,19,21,-decaene-23,24-disodium) and its tetranuclear metal complexes with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) are reported. Na4L was prepared via a template approach, which is based on the condensation reaction of sodium 2,4,6-triformyl phenolate with ethylenediamine in mole ratios of 2 : 3. The tetranuclear macrocyclic-based complexes were prepared from the reaction of the corresponding metal chloride with the ligand. The mode of bonding and overall geometry of the compounds were determined through physicochemical and spectroscopic methods. These studies revealed tetrahedral geometries about Mn, Co, and Zn atoms. However, square planar geometries have been suggested for NiII and CuII complexes. Biological activity of the ligand and its metal complexes against Gram positive bacterial strain Staphylococcus aureus and Gram negative bacteria Escherichia coli revealed that the metal complexes become more potentially resistive to the microbial activities as compared to the free ligand. However, these metal complexes do not exhibit any effects on the activity of Pseudomonas aeruginosa bacteria. There is therefore no inhibition zone

"Macrocycles, macrobicycles: a study"

A template directed [2+2] Schiff base condensation of 2,6-diformyl pyridine and 1,3 diaminopropane afforded the 20 membered Ns macrocycle "VT". The X- ray structure of the barium templated VT has been determined <M. G.B. Drew, at the University of Reading). Complexes of first transition series ions, obtained by transmetallation, have been characterized using electronic, infrared and esr spectroscopy. Results indicate that VT provides a cavity suitable for single atom bridged binuclear assemblies. The Schiff-base strategy was further used to yield macrobicyclic cyclophanes from the [2+3] condensation of tris(amino ethyl) amine ie tren, with a series of aromatic dicarbonyls. X-ray structures and 'Hnmr. studies show that these macrobicycles have very different conformations in their complexed and uncomplexed forms

Carbon dioxide cleavage by a Ni_2 complex supported by a binucleating bis(N-heterocyclic carbene) framework

A binucleating bis(N-heterocyclic carbene) ligand was designed as a means to coordinate and proximally constrain two transition metal centers. Using an imidazopyridine-based NHC afforded a framework structurally related to previously reported para-terphenyl diphosphines. Bimetallic copper, cobalt, and nickel complexes supported by this framework were synthesized and structurally characterized. Strong interactions between the metal centers and the central arene were observed in all nickel complexes. Dinickel(0) complexes of this ligand framework were found to react with CO_2 to form a dicarbonyl-bridged dinickel(0) product, demonstrating facile CO_2 reduction

Design and Synthesis of Solid State Materials Constructed from Transition Metals and Diphosphonate or Organoarsonate Ligands

This work encompasses detailed investigations of the synthesis and structures of transition metal complexes which contain xylyldiphosphonate or organoarsonate ligands. The xylyldiphosphonate families of materials which were examined were the metal(II) series of Cu, Ni, Co, Mn, Cd and Zn, with an addition of an organo-nitrogen chelate. With success in these families of materials, a secondary metal of vanadium or molybdenum was added to these metal(II) systems to increase the complexity of the structure produced. For the organoarsonate series of compounds, the chemistry of the Mo/metal(II)/organoarsonate/organo-nitrogen chelate family of materials was expanded upon and preliminary studies were conducted into the V/metal(II)/organoarsonate/organo-nitrogen chelate group of materials. The analysis of a number of structural determinants in the xylyldiphosphonate family of compounds aims to expand upon the current knowledge of metal-diphosphonate chemistry. We have focused on variables such as the xylyldiphosphonate ligand used- whether 1,4-, 1,3- or 1,2-xylyldiphosphonate. Furthermore, we have varied the denticity and size of the organo-nitrogen co-ligand. We have also investigated the incorporation of fluoride into the vanadium and molybdenum series of compounds. Through our examination of these systems we have discovered that all possible dimensionalities are represented in the xylyldiphosphonate series of compounds; we postulate that the unique flexibility of the xylyldiphosphonate ligands allows a number of unique structures to be produced. In expanding upon the organoarsonate family of materials we have discovered the preferences for molecular structures in the Mo/metal(II)/organoarsonate/organo-nitrogen chelate family of materials. In our preliminary studies of the vanadium group of materials, a one-dimensional chain was produced and with a minor change in reaction conditions we saw a drastic structural change which yielded a mixed-dimensional structure consisting of clusters and chains. We conclude that minor changes in reaction conditions can lead to large structural changes with the use of hydrothermal synthesis

Three manganese complexes of anionic N4-donor Schiff-base macrocycles: 1 monomeric Mn(II) and Mn(III), and dimeric Mn(IV)

Three manganese macrocyclic complexes of two anionic N4-donor [1+1] Schiff-base macrocycles that differ in ring size (14 vs 16 membered), HLEt and HLPr (obtained from condensation of diphenylamine-2,2’-dicarboxaldehyde and either diethylenetriamine or dipropylenetriamine), are reported. Specifically, a pair of monomeric complexes MnIILEt(NCS)(H2O) and [MnIIILPr(NCS)2]•0.5H2O, plus a dimeric complex [MnIV2LEt2(O)2](ClO4)2•3DMF have been synthesised and characterised. Single crystal structure determinations on [MnIIILPr(NCS)2]•0.5H2O and [MnIV2LEt2(O)2](ClO4)2•3DMF revealed octahedral manganese centres in both cases: N6-coordinated Jahn-Teller distorted Mn(III) in the former and a pair of N4O2-coordinated Mn(IV) in the latter. UV-vis, IR and EPR spectroscopy as well as magnetic measurements are reported. These macrocyclic complexes feature a simple and original design, and could find future uses as models for manganese catalase or as building blocks for the assembly of larger supramolecular architectures

The synthesis of the cyclometallated palladium complexes and their applications in olefin oligomerization and in phenylacetylene oligomerization/polymerization

Magister Scientiae - MScThis thesis reports the synthesis of the imine ligands from Schiff base condensation reaction of aldehyde derivatives and equimolar quantities of aniline derivatives. The imine ligands spectrometry

Encapsulated Metal Ions: Mononuclear and Binuclear Complexes of Schiff-Base Macrocycles and Cryptands

Schiff-base condensation of 2,6-dlacetylpyridine with diamines on Pb(II) afforded complexes of binucleating [2+2] macrocyclic ligands P (1) and MC (2). The complexes were isolated as the dilead macrocyclic tetrathiocyanate. Interest derives from the unusual binding mode of thiocyanate as a single atom 'N-only' bridge between the pair of lead ions bound by the macrocycle. An X-ray crystallographic structure determination, carried out by Dr. V .McKee, on the dilead MC complex demonstrates the existence of a single thiocyanate 'N-only' bridge between the lead ions. The N-only bridging mode of thiocyanate is retained in derivatives containing two or three triflate anions. Transmetallation of the P complex, Pb2P(NCS)4 with transition metal triflates gave homobinuclear products with M = Cu(II), Co(II) and heterobinuclear Pb/M products with M = Mn(II), Fe(II), Ni(II), whereas transmetallation of the dilead MC complex afforded homobinuclear Cu(II) and Ni(II) complexes and heteroblnuclear complexes with M = Mn(II) and Fe(II). Infrared spectra suggest that the 'N-only' bridging mode of thiocyanate exists between the metal ions in the heterobinuclear MnPbMC and FePbMC complexes and X-ray structural confirmation has been obtained for the manganese/lead MC complex. There was evidence of the existence of heterobinuclear FeCuP and FeCuMC complexes which were formed by metal exchange of the lead ion, in the respective FePb macrocyclic complex, for Cu(I). The cryptand GT, (3) was farmed by Schiff-base condensation of the tripod amine N(CH2CH2NH2)3 with glyoxal, using group (11) metal ions as template. A wide range of metal ion GT cryptates were obtained by transmetallation, including transition metal ion, lanthanide ion and group(1) metal ion cryptates. An X-ray crystal structure of the cobalt(II) GT cryptate has been obtained. Generally the cryptates are mononuclear with respect to the metal ion, an exception being the binuclear copper (I) cryptate. Transmetallation with copper (ID produces either the mononuclear or the dinuclear cryptate depending on conditions employed. The binuclear copper(II) cryptate has a particularly unusual 7-line esr spectrum which suggests formation of a mixed valence Cu(II)/Cu(I) species. Cyclic voltammetry has shown strong stabilisation of the Cu(I) state, with E½ for the reduction lying in the range found for blue copper proteins. Synthesis of transition metal ion complexes by transmetallation of disilver or dilead 3Bp (4), or metal ion insertion into the 3Bp ligand was investigated. Dicobalt(II) and dicopper (I) cryptates of 3Bp were obtained. The corresponding reduced metal-free cryptand, R3Bp (5), gave an interesting series of binuclear complexes of Ni(II), Cu(I), Cu(II) and Co(II). The dicopper(II) and dicobalt(II) cryptates are of particular interest due to the presence of a hydroxo bridge between the metal ions. Attempted insertion of Mn(II) into R3Bp failed but gave the tetraprotonated R3Bp triflate whose structure was crystallographically determined. Attempts to insert metal ions into cryptand 3Bm (6) failed. However insertion of Ni(II) gave ring opening and a pendant arm macrocyclic complex was obtained. The reduced metal-free ligand, R3Bm (7) produced a wider range of complexes, including the dinickel(II), dicopper(II) and dicobalt(II) cryptates. Transition metal complexes throughout, have been characterised using infrared, electronic, and e.s.r. spectroscopy. Magnetic susceptibility measurements and n.m.r. were employed where appropriate. The work described in Chapters 2, 3, 4 and 5 is preceeded by a review of the relevant literature, in Chapter 1

Polynuclear complexes of macrocyclic and related ligands

A route to sodium salts of tetranuclear Schiff-base macrocyclic ligands (H2Na2L1and H2Na2L2) derived from the condensation of 2,6-diformyl-4-(methyl or tert-butyl) phenol and 1,5-diaminopentan-3-ol has been developed, in order to compare two synthetic pathways namely the template synthesis and the "direct" synthesis of already known tetranuclear macrocyclic complexes. Subsequently, the complexation of H2Na2L1 and H2Na2L2 with nickel(II), copper(II), cobalt(II) and manganese(II) has been performed. The X-ray structures of tetranuclear nickel(II), copper(II) and manganese(II/III) complexes synthesised via the non-template route were determined and discussed. Furthermore, it is shown that the synthesis of tetranuclear complexes of metals inert towards template reactions like palladium is possible by complexing the pre-formed macrocycles H2Na2L1 and H2Na2L2. [Continues.

Synthesis, X-ray crystal structures, electrochemistry and theoretical investigation of a tetradentate nickel and copper Schiff base complexes

International audienceNew tetradentate mononuclear nickel(II) [NiL] and pentadentate binuclear copper(II) [Cu 2 L 2 H 2 O], H 2 O Schiff base complexes have been synthesized. The crystal structures of [NiL] and [Cu 2 L 2 H 2 O], H 2 O have been determined by X-ray diffraction method showing distorted square-planar geometry for [NiL] and distorted tetragonal pyramid geometry for [Cu 2 L 2 H 2 O], H 2 O. In both complexes, the dehydroacetic acid functional group engages in a deprotonated manner and coordination occurs through the nitrogen atoms of the imine function and the phenolic oxygen. Density Functional Theory calculations are carried out for the determination of the optimized structures. The fundamental vibrational wave numbers are calculated and a good agreement between observed and calculated wave numbers is achieved