Synthesis, characterization and catalytic oxidation of cyclohexene with molecular oxygen with host (nanopores of zeolite-Y)/guest (Ni(II) complexes of 14- and 16-membered tetraaza dioxo diphenyl macrocyclic ligands) nanocomposite materials

Ni(II) complexes of [14]aneN₄: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane; [16]aneN₄: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane; Bzo₂[14]aneN₄: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and Bzo₂[16]aneN₄: dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane have been encapsulated in the nanopores of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)nickel(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Ni(N–N)₂]²⁺–NaY; in the nanopores of the zeolite-Y, and (ii) in situ condensation of the nickel(II) precursor complex with ethylcinnamate. The new host–guest nanocomposite materials (HGNM) were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/Vis, XRD and DRS) and the BET technique. These complexes were used for oxidation of cyclohexene with molecular oxygen.     

Host (nanopores of zeolite-Y)/guest (Ni(II)-tetraoxo dithia tetraaza macrocyclic complexes) nanocomposite materials: template synthesis and characterization

Nickel(II) complexes with six co-ordinate tetraoxo dithia tetraaza macrocyclic ligands derived from diamine and which provide a N₄S₂ co-ordination sphere, [18]aneN₄S₂: 1,4,10,13-tetraaza-5,9,14,18-tetraoxo-7,16-dithia-cyclooctadecane, [20]aneN₄S₂: 1,5,11,15-tetraaza-6,10,16,20-tetraoxo-8,18-dithia-cyclocosane, Bzo₂[18]aneN₄S₂: dibenzo-1,4,10,13-tetraaza-5,9,14,18-tetraoxo-7,16-dithia-cyclooctadecane, Bzo₂[20]aneN₄S₂: dibenzo-1,5,11,15-tetraaza-6,10,16,20-tetraoxo-8,18-dithia-cyclocosane, were entrapped in the nanopores of zeolite NaY by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)nickel(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Ni(N–N)₂]²⁺-NaY; in the nanopores of the zeolite, and (ii) in situ template condensation of the nickel(II) precursor complex with thiodiglycolic acid. The mode of bonding and overall geometry of the complexes and new host/guest nanocomposite materials ([Ni([18]aneN₄S₂)]²⁺-NaY, [Ni([20]aneN₄S₂)]²⁺-NaY, [Ni(Bzo₂[18]aneN₄S₂)]²⁺-NaY, [Ni(Bzo₂[20]aneN₄S₂)²⁺-NaY) has been inferred through FT-IR, DRS and UV–vis spectroscopic techniques, molar conductance and magnetic moment data, XRD and elemental analysis, as well as nitrogen adsorption. An octahedral geometry around the nickel(II) ion is suggested for the complexes and new host/guest nanocomposite materials.     

The preparation of a series of 12-, 13- and 14-membered tetra-imine macrocycles and characterization of their copper(II) complexes

Summary The 12-, 13- and 14-membered tetraphenyl substituted macrocycles Ph₄[12]TIM (2,3,8,9-tetraphenyl-1,4,7,10-tetra-azacyclododeca-1,3,7,9-tetraene), Ph₄[13]TIM (2,3,8,9-tetraphenyl-1,4,7,10-tetra-azacyclotrideca-1,3,7,9-tetraene) and Ph₄[14]TIM (2,3,9,10-tetraphenyl-1,4,8,11-tetradeca-1,3,8,10-tetraene) were prepared and their copper(II) complexes characterised. Magnetic and spectroscopic measurements (i.r. and u.v.-vis.) are discussed. A variety of macrocyclic precursers (KIM = 1,2,8,9-tetraphenyl-3, 7-diaza-2,7-dione) and KIM-dioxime were also prepared and characterised.     

An economical synthesis of dibenzocyclamnickel(II) and a metal-free macrocycle with tetramethyl substituents

The cationic dibenzocyclamnickel(II) complex, [Ni(Me₄Bzo₂[14]aneN₄)]²⁺, was obtained in good yield by Fe/HCl reduction of the corresponding tetraazaannulene complex [Ni(Me₄taa)], (1) {Me₄Bzo₂[14]aneN₄ = 5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazacyclotetradecane; Me₄taa = 5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazaannulene(2-)}. The orange–red product was isolated as the chloride (2) and perchlorate (3) salts. Analogous reduction with Zn/HCl yielded a diprotonated silky-white product [Ni(Me₄Bzo₂[14]aneN₄-H₂)][ZnCl₄]₂, (4). In the dry state, complex (4) is stable only under an HCl atmosphere and readily dissociates to give a solution of (2) when dissolved in polar solvents. Complexes (2) and (3), upon treatment with an excess of aqueous NaCN, undergo facile demetallation yielding the metal free macrocycle Me₄Bzo₂[14]aneN₄, (5). These compounds were characterized using a combination of i.r., u.v.–vis., ¹H-n.m.r., mass spectroscopy and voltammetry techniques. Unlike the parent tetraazaannulene complex (1), the reduced macrocycle complex, [Ni(Me₄Bzo₂[14]aneN₄)]²⁺ exhibits mild catalytic activity towards electro-reduction of CO₂ in MeCN solution.     

Influence of the Coordination of Donor Solvent Molecules to 1,4,7,10-Tetramethyl-1,4,7,10- tetraazacyclododecanenickel(II) and Analogous Nickel(II) Complexes on Their Steric Factors

Coordination equilibrium constants (K _NiS) of some donor solvent molecules to 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecanenickel(II) ([Ni(Me₄[12]aneN₄)]²⁺) were determined in nitrobenzene (a noncoordinating bulk solvent). The first (K _NiS1) and second stepwise coordination equilibrium constants (K _NiS2) for 1,4,7,10-tetraazacyclododecanenickel(II) ([Ni([12]aneN₄)]²⁺), 1,4,8,11-tetraazac yclotetradecane- nickel(II) ([Ni([14] aneN₄)]²⁺), 1,4,8,11-tetrathiacyclotetra-decanenickel(II) ([Ni([14]aneS₄)]²⁺) were also reinvestigated. The K _NiS values for [Ni(Me₄[12]aneN₄)]²⁺ were compared to those of [Ni([12]aneN₄)]²⁺, (1R,4S, 8R,11S)-1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) (R,S,R,S-[Ni(Me₄[14]aneN₄)]²⁺), R,R,S,S-[Ni(Me₄[14]aneN₄)]²⁺, [Ni([14]aneN₄)]²⁺, and [Ni([14]aneS₄)]²⁺. Coordination of pyridine (Py), N,N,N′,N′-tetramethylurea (TMU), and N,N-dimethylacetamide (DMA) to [Ni(Me₄[12]aneN₄)]²⁺ was observed, although these donor solvent molecules did not coordinate to R,S,R,S-[Ni(Me₄[14]aneN₄)]²⁺. The K _NiS values for Py, TMU, and DMA are 7.9, 2.8, and 9.0 dm³⋅mol⁻¹, respectively. Some hydrogen-bonding waters were coordinated to R,S,R,S-[Ni(Me₄[14]aneN₄)]²⁺, but such waters did not coordinate to [Ni(Me₄[12] aneN₄)]²⁺. Also, the K _NiS2 values were larger than the corresponding K _NiS1 values for [Ni([14]aneS₄)]²⁺. Furthermore, the K _NiS1 values for [Ni([12]aneN₄)]²⁺ were the largest among these nickel(II) complex cations. The K _NiS, K _NiS1, and K _NiS2 values are discussed in terms of properties of the donor solvents and steric strains of these nickel(II) complex cations.     

Synthesis, characterization of cobalt(II) complex nanoparticles encapsulated within nanoreactors of zeolite-Y and their catalytic activities

Cobalt(II) complex nanoparticles of [14]aneN₄: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane; [16]aneN₄: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane; Bzo₂[14]aneN₄: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and Bzo₂[16]aneN₄: dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane have been encapsulated in the nanopores of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)cobalt(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Co(N–N)₂]²⁺–NaY; in the nanopores of the zeolite-Y, and (ii) in situ condensation of the cobalt(II) precursor complex with ethylcinnamate. The new complex nanoparticles entrapped in the nanoreactor of zeolite-Y were characterized by several techniques: BET, chemical analysis and spectroscopic methods (FT-IR, UV–vis, XRD, and DRS). These complexes (neat and encapsulated) were used for epoxidation of styrene with O₂ as oxidant in different solvents. Electronic spectra of the reaction mixture indicated that the oxidation proceeds through a free radical mechanism.     

Template synthesis and characterization of host (nanopores of zeolite Y)/guest (Co(II)-tetraoxodithiatetraaza macrocyclic complexes) nanocomposite materials

A series of Co(II) tetraoxodithiatetraaza macrocyclic complexes ([18]aneN₄S₂, [20]aneN₄S₂, Bzo₂[18]aneN₄S₂ and Bzo₂[20]aneN₄S₂) have been encapsulated in the nanopores of zeolite Y by template condensation reaction. Co(II) complexes with tetraoxodithiatetraaza macrocyclic ligand were entrapped in the nanopores of zeolite Y by a two-steps process in the liquid phase: (i) ion-exchange of [bis(diamine)cobalt(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Co(N–N)₂]²⁺–NaY; in the nano-cavity of the zeolite, and (ii) in situ template condensation of the cobalt(II) precursor complex with thiodiglycolic acid. The mode of bonding and overall geometry of the complexes and new host/guest nanocomposite materials ([Co([18]aneN₄S₂)]²⁺–NaY, [Co([20]aneN₄S₂)]²⁺–NaY, [Co(Bzo₂[18]aneN₄S₂)]²⁺–NaY, [Co(Bzo₂[20]aneN₄S₂)²⁺–NaY) has been inferred through FT-IR, DRS and UV–Vis spectroscopic techniques, BET technique, molar conductance and magnetic moment data, XRD and elemental analysis, as well as nitrogen adsorption. The average number of encapsulated Co complexes per nano-cavity was determined to be 0.33 for the Co complexes–NaY. An octahedral geometry around the cobalt(II) ion is suggested for the complexes and new host/guest nanocomposite materials.     

Benzoylation of macrocyclic jäger type Ni(II) complexes and an efficient demetalation of γ,γ′-dibenzoylated products

The reaction of [Bzo₂Me₄[14]hexaenato(2?)N₄]Ni(II) and [Bzo₂Me₂Ph₂[14]hexaenato(2?)N₄]Ni(II) with benzoyl chloride leading to mono- and disubstituted derivatives is reported. The condition of the reliable demetalation of γ,γ′-dibenzoylated complexes by means of gaseous HCl are described. The Cu(II) complexes are synthesized from free ligands. All new compounds are characterized by elemental analysis, IR, ¹H NMR and MS data.     

SYNTHESIS AND COMPLEX FORMATION OF NOVEL 12-MEMBERED MACROCYCLIC (E,E)-DIOXIMES

Abstract

Dibenzo[e,k]-2,3-bis(hydroxyimino) 1.4.7.10-tetrathia-2,3,8,9-tetrahydrocyclododecine (S₄H₂) and dibenzo-[e,k]-2,3-bis(hydroxyimino)-1,4-dithia-7,10-dioxa-2,3,8,9- tetrahydrocyclododecine (O₂S₂H₂) have been prepared from (E,E)-dichloroglyoxime, 2,3,8,9-dibenzo-1,4,7,10-tetrathiadecane (DTT) and 2,3,8,9-Dibenzo-4,7-dioxa-1,10-dithiadecane (DDD) which was synthesized by treating 1,2-bis(o-aminophenoxy)ethane with HNO₂ and potassium ethylxsanthate. The structures of these vic-dioximes have been determined as the (E,E)-forms according to ¹H-NMR and IR data. Only mononuclear complexes with a metal-ligand ratio of 1:2 have been isolated with Co(II), such as [(S₄H)₂Co(III)L′Cl] and [(O₂S₂H)₂Co(III)L′Cl]; Cu(II) forms only trinuclear complexes. Reaction of the mononuclear complexes with Pd(II) gives heterotrinuclear complexes.     

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.     

Kinetic studies of the interaction between organotin(IV)chlorides and tetraaza Schiff bases: Synthesis and characterization of some novel tin(IV) Schiff base complexes

In this article the kinetics of the interaction between the teteraaza Schiff bases as donor with organotin(IV)chlorides as acceptor was studied in acetonitrile. Teteraaza Schiff bases are (Me₄‐Bzo₂[14]tetraeneN₄) (tmtaa), (Me₄‐4‐CH₃Bzo₂[14]tetraeneN₄) (Metmtaa), (Me₄‐4‐ClBzo₂[14]tetraeneN₄) (Cltmtaa), i.e., [(Me₄‐Bzo₂[14]tetraeneN₄)] means that (5,7,12,14‐tetramethyldibenzo[b,i][1,4,8,11] tetraazacyclotetradecine) (tmtaa) and organotin(IV)chlorides are methyltin(IV) trichloride, phenyltin(IV)trichloride, dimethyltin (IV)dichloride, diphenyltin(IV) dichloride, and dibutyltin(IV)dichloride. The kinetic parameters and the second‐order k₂ rate constants show the donor properties of tetraaza Schiff bases as Me₄‐4‐CH₃Bzo₂[14]tetraeneN₄ > Me₄‐Bzo₂[14]tetraeneN₄ > Me₄‐4‐ClBzo₂[14]tetraeneN₄ and also the acceptor properties of organotin(IV)chlorides as PhSnCl₃ > MeSnCl₃ > Ph₂SnCl₂ > Me₂SnCl₂ > Bu₂SnCl₂. An excellent linearity of k_obs vs. the molar concentration of the acceptor, the high span of k₂ values, the large negative values of ΔS^≠, and the low ΔH^≠ values suggest an associative (A) mechanism for the acceptor–donor interaction. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 247–254, 2011     

Complexes of 1-thia-4,7,10-triazacyclododecane ([12]aneN3S): Synthesis,structure and stability constants

The 12-membered macrocyclic ligand 1-thia-4,7,10-triazacyclododecane ([12]aneN₃S) has been synthesised, although upon crystallization from acetonitrile a product in which carbon dioxide had added to one secondary amine in the macrocyclic ring (H[12]aneN₃S–CO₂·H₂O) was isolated and subsequently characterised by X-ray crystallography. The protonation constants for [12]aneN₃S and stability constants with Zn(II), Pb(II), Cd(II) and Cu(II) have been determined either potentiometrically or spectrophotometrically in aqueous solution, and compared with those measured or reported for the ligands 1-oxa-4,7,10-triazacyclododecane ([12]aneN₃O) and 1,4,7,10-tetraazacyclododecane ([12]aneN₄). The magnitudes of the stability constants are consistent with trends observed previously for macrocyclic ligands as secondary amine donors are replaced with oxygen and thioether donors although the stability constant for the [Hg([12]aneN₄)]²⁺ complex has been estimated from an NMR experiment to be at least three orders of magnitude larger than reported previously. Zinc(II), mercury(II), lead(II), copper(II) and nickel(II) complexes of [12]aneN₃S have been isolated and characterised by X-ray crystallography. In the case of copper(II), two complexes [Cu([12]aneN₃S)(H₂O)](ClO₄)₂ and [Cu₂([12]aneN₃S)₂(OH)₂](ClO₄)₂ were isolated, depending on the conditions employed. Molecular mechanics calculations have been employed to investigate the relative metal ion size preferences of the [3333], asym-[2424] and sym-[2424] conformation isomers. The calculations predict that the asym-[2424] conformer is most stable for M–N bond lengths in the range 2.00–2.25 Å whilst for the larger metal ions the [3333] conformer is dominant. The disorder seen in the structure of the [Zn([12]aneN₃S)(NO₃)]⁺ complex is also explained by the calculations.     

Copper(II) complexes with 18-membered decaaza macrocycles: synthesis,characterization and catalytic activity

New square-planar copper(II) complexes of 18-membered decaaza macrocyclic ligands: 5,6,14,15-tetramethyl-1,3,4,7,8,10,12,13,16,17-decaazacyclooctadecane (Me₄[18]aneN₁₀); 1,10-dimethyl-(Me₂Me₄[18]aneN₁₀); 1,10-diethyl-(Et₂Me₄[18]aneN₁₀); 1,10-dipropyl-(Pr₂Me₄[18]aneN₁₀); 1,10-dibutyliso-(Bu₂Me₄[18]aneN₁₀) and 1,10-dibenzyl-5,6,14,15-tetramethyl-1,3,4,7,8,10,12,13,16,17-decaazacylooctadecane [(Benzyl)₂Me₄[18]aneN₁₀)] have been prepared by a one-pot template condensation of formaldehyde and 2,3-butanedihydrazone with alkyl and benzylamine in the presence of copper(II) ion. The complexes of the decaaza macrocycle have been characterized by elemental analyses, i.r., u.v.–vis., conductometric and magnetic measurements. The spectra of [Cu(R₂Me₄[18]ane N₁₀)](ClO₄)₂shows that the four nitrogen (α-diimine) atoms are coordinated to the copper(II) ion. These complexes are found to be effective catalysts for the selective oxidation of tetrahydrofuran to yield the corresponding tetrahydrofuran-2-one and a small amount of tetrahydrofuran-2-ol and 4-hydroxybutyraldehyde, using diluted H₂O₂ as the oxidant.     

Nickel(II) compounds of a tri-amine mono-imine macrocycle: Preparations and structures of (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II) compounds

Reduction of one imine function of (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)nickel(II) with 1 molar proportion of NaBH₄ produces as the major product the tri-amine-mono-imine macrocyclic cation (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradec-4-ene)nickel(II), Ni(tm)]²⁺. Pairs of isomeric singlet ground state perchlorate and tetrachlorozincate salts of [Ni(tm)]²⁺ were prepared and the structures determined for the 1RS,8SR,11SR,12RS (labeled as β) and 1RS,8RS,11RS,12SR (labeled as α) tetrachlorozincate salts. Triplet ground state trans-β-[Ni(tm)(NCS)₂] and catena-trans-{β-Ni(tm)-NC-Ni(CN)₂-CN-}_n·2nH₂O have the macrocycle in planar coordination and α-[{Ni(tm)}₂(C₂O₄)](ClO₄)₂ has the macrocycle folded. With pentane-2,4-dione the compounds [β-Ni(tm)]·[α-Ni(tm)(acac)](ClO₄)₃ and [Ni(teta)]·[α-Ni(tm)(acac)](ClO₄)₃ (teta = C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) with both square-planar and octahedral Ni(II) cations were prepared and the latter was structurally characterized. Isomerisation in solution of metastable α-[Ni(tm)]²⁺ to stable β-[Ni(tm)]²⁺ is extremely slow, even in base.     

Template synthesis and characterization of cobalt(II) complex nanoparticles entrapped in the zeolite-Y

Zeolite encapsulated complex nanoparticles “[Co([18]py₂N₄)]²⁺, [Co([20]py₂N₄)]²⁺, [Co(Bzo₂[18]py₂N₄)]²⁺ or [Co(Bzo₂[20]py₂N₄)]²⁺” were successfully prepared by the template synthesis of 2,6-diacetylpyridine with [Co(N–N)₂]²⁺ (N–N = 1,2-diaminoethane, 1,3-diaminepropane, 1,2-diaminobenzene, 1,3-diaminobenzene) within the zeolite-Y. These complex nanparticles were entrapped in the Y-zeolite by a two-step process in the liquid phase: (i) inclusion of a Co(II) precursor complex, [Co(N–N)₂]²⁺@NaY, and (ii) template synthesis of the cobalt(II) precursor complex with the 2,6-diacetylpyridine. The new complex nanoparticles entrapped in the zeolite Y “[Co([18]py₂N₄)]²⁺@NaY, [Co([20]py₂N₄)]²⁺@NaY, [Co(Bzo₂[18]py₂N₄)]²⁺@NaY, [Co(Bzo₂[20]py₂N₄)]²⁺@NaY” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XPS, XRD, BET, DRS). Analysis of the data indicates that the cobalt(II) complex nanoparticles are encapsulated in the zeolite-Y and exhibit different property from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix.     

Structure and Kinetics of Oxidation of Amphiphilic Nickel(II) Pentaazamacrocycles by Peroxodisulfate and by a Nickel(III) Pendant-Arm Macrocycle

Three nickel(II) pentaazamacrocycles bearing pendant alkyl tails have been synthesized,and the crystal structure of one (bearing an octyl tail) is reported. The redox potentials of the complexes, for oxidation of the nickel(II) centre, is 0.72 V (versus S.H.E.) in all cases, indicating that the pendant alkyl tails have no effect on the redox site. The kinetics of oxidation of the complexes by peroxodisulfate, S₂O₈ ^2- and by aqua(5, 5, 7,12, 12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato)nickel(III),[Ni(hmca)(OH₂)]²⁺ have been studied. Oxidation by S₂O₈ ^2- occursby ion-pairing of the reactants, followed by electron transfer with concomitant peroxo bond fissure. Oxidation by [Ni(hmca)(OH₂)]²⁺ occurs by an outer sphere electron transfer process. Redox kinetics at the nickel centre provides a probe for supramolecular interactions at the pendant tails in such complexes.     

Host (nanocavity of zeolite Y)/guest (Co(II), Ni(II) and Cu(II) complexes of unsaturated 16-membered octaaza; 3,4,11,12-tetramethyl-1,2,5,6,9,10,13,14-octaazacyclohexadecane; Me4[16]aneN8 nanocomposite materials (HGNM): template synthesis, characterization and catalytic oxidation of benzyl alcohol

Nanocavity zeolite-Y (host) encapsulated Co(II), Ni(II) and Cu(II) complexes of unsaturated 16-membered octaaza; 3,4,11,12-tetramethyl-1,2,5,6,9,10,13,14-octaazacyclohexadecane ‘Me₄[16]aneN₈’; macrocycle (guest) were synthesized and characterized by chemical analyses, s.e.m., x.r.d., u.v.–vis., d.r.s., surface area, pore volume, conductometric, magnetic measurements and i.r. spectroscopy with a view to confirming the encapsulation of complexes and to arrive at the composition, structure and geometry of encapsulated complexes. The characterization data show the absence of extraneous complexes, retention of zeolite crystaline structure and encapsulation in the nanocavities. Host–Guest Nanocomposite Materials (HGNM) ‘[M(Me₄[16]aneN₈)]²⁺-NaY’ are catalytically very efficient as compared to other neat complexes for the partial oxidation of benzyl alcohol which is stable and becomes recycled without much deterioration.     

Synthesis of poly(4-vinylpyridine) and block copoly (4-vinylpyridine-b-styrene) by atom transfer radical polymerization using 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazamacrocyclotetradecane as ligand

Poly(4-vinylpyridine) (P4VP) and block copolymer, poly(4-vinylpyridine-b-styrene) (P4VP-b-PSt) were prepared by atom transfer radical polymerization (ATRP) using 1-phenylethyl chloride as initiator, CuCl and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazamacrocyclotetradecane (Me₆[14]aneN₄) as catalyst and ligand. The polymerization of 4VP was carried out in 2-propanol at 40 °C. GPC and NMR studies show that the plot of ln([4VP]₀/[4VP]) against the reaction time is linear, and the molecular weight of the resulting P4VP increased linearly with the conversion. Within 3 h, the conversion can reach almost 90%. P4VP-b-PSt amphiphilic block copolymer with low polydispersity index (M_w/M_n ≈ 1.2) is also obtained by ATRP of St in DMF at 110 °C using P4VP-Cl as macroinitiator, CuCl/ Me₆[14]aneN₄ as catalyst.     

Synthesis,Crystal Structure and Magnetic Properties of an Oxalato-Bridged Dinickel(II) Complex Containing A MacrocyClic Ligand

A new binuclear nickel(II) complex [Ni(µ-C₂O₄)(rac-cth)₂](ClO₄)₂[rac-cth = rac -5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane] has been prepared and its structure determined. It consists of centrosymmetric [Ni( µ -C₂O₄)(rac-cth)₂]²⁺ cations separated by perchlorate anions, with a centre of symmetry lying in the middle of the C-C bond of the bis-bidentate oxalate bridge. The tetraazamacrocycle adopts a folded conformation around the nickel atom, which is six coordinated in a distorted octahedral arrangement. Variable temperature magnetic susceptibility measurements (4-300 K) suggest a moderate intramolecular antiferromagnetic interaction between the metal ions ( J = -34.0 cm^-1, g = 2.07)     

Formation and isomerisation of theO-sulphito complex of 1,4,7,10,13-penta-azacyclohexadecanecobalt(III)

Summary Dissolved SO₂ reacts rapidly with [Co([16]aneN₅)OH]²⁺ to give [Co([16]aneN₅OSO₂]⁺([16]aneN₅=1,4,7,10, 13-penta-azacyclohexadecane), which on immediate acidification loses SO₂ to give [Co([16]aneN₅)OH₂]³⁺. The O-bonded sulphito complex (_max 526 nm) undergoes a slow linkage isomerisation to give the S-bonded species [Co([16]aneN₅)SO₃]⁺ (_max 466 nm), rather than an internal redox reaction. The S-bonded complex has been isolated and characterised as the perchlorate salt [Co([16]aneN₅) (SO₃H)](ClO₄)₂.