Binuclear Nickel Complexes Research Articles

Novel highly active binuclear neutral nickel and palladium complexes as precatalysts for norbornene polymerization

A series of binuclear neutral nickel and palladium complexes [(XC 6H 2CH NC 6H 3- iPr 2)MRL] 2 4b– f (X = NO 2, M = Ni, R = Ph, L = PPh 3, 4b; X = H, M = Pd, R = Me, L = PPh 3, 4c; X = H, M = Pd, R = Me, L = Py, 4d; X = NO 2, M = Pd, R = Me, L = PPh 3, 4e; X = NO 2, M = Pd, R = Me, L = Py, 4f) and [(C 10H 7CH NC 6H 3- iPr 2)MRL] 2 8a– c (M = Ni, R = Ph, L = PPh 3, 8a; M = Pd, R = Me, L = PPh 3, 8b; M = Pd, R = Me, L = Py, 8c) have been synthesized and characterized. The structures of complexes 4e and 8b have also been confirmed by X-ray crystallographic analysis. With modified methylaluminoxane (MMAO) as cocatalysts, these complexes and complex [(C 6H 3CH NC 6H 3- iPr 2)NiPh(PPh 3)] 2 4a are capable of catalyzing the addition polymerization of norbornene (NBE) with the high activity up to 2.3 × 10 8 g PNBE/(mol M h). The structure of complexes affects considerably catalytic activity towards norbornene polymerization. The polymers obtained with nickel complexes are soluble, while those obtained with palladium complexes are insoluble. Palladium complexes 4c, 4e and 8b bearing PPh 3 ligands exhibit much higher activities than the corresponding complexes 4d, 4f and 8c bearing pyridine ligands under the same conditions.

Binuclear neutral nickel complexes bearing bis(bidentate) salicylaldiminato ligands: Synthesis, structure and ethylene polymerization behavior

Reaction of sodium salts of the bridging [O,N,N,O]-type bisalylaldimine ligands [O,N,N,O = [3-phenyl-2-OH-(CH N)] 2-L (L = CH 2CH 2CH 2 3a, 1,4-C 6H 4 3b)] with trans-bis(triphenylphosphane)phenylnickel (II) chloride result in neutral bis(bidentate) binuclear nickel (II) complexes 4a and 4b. The structure of 4b has been confirmed by X-ray crystallography. 4a shows moderate activity for polymerization of ethylene in the presence of methylaluminoxane (MAO). Catalytic activities, molecular weights and molecular weight distribution of polyethylene have been investigated under the various reaction conditions.

Binuclear Copper(II), Nickel(II) and Cobalt(II) Complexes with N2O2 Chromophores of Glycylglycine Schiff-Bases of Acetylacetone, Benzoylacetone and Thenoyltrifluoroacetone

Binuclear copper, nickel and cobalt complexes of the Schiff-bases obtained by condensation of glycylglycine with acetylacetone, benzoylacetone, dibenzoylmethane and thenoyltrifluoroacetone were prepared by template synthesis. The complexes were characterized by elemental analysis, conductivity measurements, magnetic moments, i.r., u.v.–vis. spectra, e.s.r., X-ray diffraction, t.g.a., d.t.a. and d.s.c. thermal analysis. All the complexes are non-electrolytes with low magnetic moments that indicate spin–spin or antiferromagnetic exchange interactions. Spectral properties support square planar and square pyramidal or trigonal bipyramidal structure provided by the N2O2 chromophores. E.s.r. spectra of the copper complex confirm the binuclear structure and the presence of magnetic interaction. Thermal studies supported the chemical formulation of these complexes and showed that they decompose in three to four steps depending on the type of ligand. Activation energies Ea and enthalpies ΔH, associated with the thermal decomposition of the complexes were calculated and correlated with the type of complexed metal. A mechanism for thermal decomposition is proposed for the complexes.

Synthesis and characterization of 4-(alkylaminoisonitrosoacetyl)biphenyls and their complexes

Three new substituted 4-(alkylaminoisonitrosoacetyl)biphenyls (ligands) derived from 4-biphenylhydroxymoyl chloride and corresponding amines were synthesized. The following aromatic and aliphatic amines were used for ligands: ethanolamine, 2-amino-4-methylphenol, and 2-(aminomethyl)pyridine. Mononuclear or binuclear cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and lead(II) complexes with these ligands were synthesized. These compounds were characterized by elemental analyses, AAS, infrared spectra, and magnetic susceptibility measurements. The ligands were additionally characterized by 1H NMR. The results suggest that the ligands act as tridentate ligands.

Binuclear transition-metal trimethylacetato complexes containing coordinated 3,5-dimethylpyrazole as structural analogues of the active site of natural metalloenzymes

Synthetic approaches are discussed to prepare binuclear trimethylacetato complexes of zinc, copper, cobalt, and nickel containing an M2(μ-OOCR)2L4 binuclear fragment, which is found in the active site of natural metalloenzymes.

Structural and Spectroscopic Features of Mono- and Binuclear Nickel(II) Complexes with Tetradentate N(amine)2S(thiolate)2 Ligation

Three complexes containing Ni(II)N(amine)2S(thiolate)2 units have been prepared and characterized. Both (R,R)-N,N'-bis(1-carboxy-2-mercaptoethyl)-1,2-diaminoethane [(R,R)-1] and N,N'-bis(2-methyl-2-mercaptoprop-1-yl)-1,3-diamino-2,2-dimethylpropane (4) act as tetradentate S-N-N-S ligands to form complexes Ni((R,R)-1) and Ni4 with nearly planar cis-NiN2S2 units. The N-Ni-N and S-Ni-S angles differ significantly in the two complexes yet are very nearly supplementary. The 1,3-disubstituted cyclohexane species rac-N,N'-bis(2-mercapto-2-methylprop-1-yl)-1,3-cyclohexanediamine (6) behaves as a bis(bidentate-N,S) ligand to form an unexpectedly intense-blue dinickel complex (1S,3R,1'S,3'R)-7, which contains two trans-NiN2S2 units bridged by 1,3-disubstituted cyclohexane groups. The coordination geometry in (1S,3R,1'S,3'R)-7 is distorted 15 degrees toward tetrahedral, most likely as a result of steric crowding, suggested by several short contacts between the NiS2 units and both the cyclohexyl and gem-dimethyl groups of the N,S-chelate rings. The complexes exhibit rich UV-vis spectra, whose deconvoluted bands are now fully assigned, from low to high energy, as ligand field (LF), pi(S) --> Ni(II) ligand-to-metal charge transfer (LMCT), sigma(S) --> Ni(II) LMCT, sigma(N) --> Ni(II) LMCT, localized S, and S,N Rydberg transitions. The unusually intense LF absorptions shown by (1S,3R,1'S,3'R)-7 are thought to result from relaxation of the Laporte restriction arising from the 15 degrees tetrahedral twist.

Lateral macrobicyclic compartmental mono and binuclear nickel(II) complexes derived from phenolate ligands: Synthesis, spectral, electrochemical and kinetic studies

A novel macrobicyclic ditopic ligand derived from the precursor compound 3,4:10,11-dibenzo-1,13[ N, N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,9-dioxocycloheptadecane has been synthesized in the presence of metal ion via template method. Various mono and binuclear nickel(II) complexes of type [NiL](ClO 4) and [Ni 2L](ClO 4) 2 have been synthesized in order to examine electrochemical and kinetic studies on the basis of macrocyclic ring size. Cyclic voltammetry and controlled electrolysis studies indicate that the nickel(II) complexes undergo quasireversible one electron reduction and oxidation. All the nickel(II) complexes have square planar geometry and EPR silent. The examination of kinetics of the hydrolysis of 4-nitrophenyl phosphate vindicates that the catalytic activities of the complexes are found to increase with macrocyclic ring size of the complexes. As, the macrocyclic ring size of the complexes increases, the spectral, electrochemical and catalytic studies of the complexes show remarkable variation due to distortion in the geometry around nickel(II) centre.

Mesogenic Properties of Binucleating Schiff-Base Ligands with Long Side Chains and Their Binuclear Cu(II) and Ni(II) Complexes

ABSTRACT Liquid-crystalline binucleating ligands, 1,4-[bis(2-hydroxy-4-(n-alkoxy)benzaldimino]benzene, and their binuclear nickel and copper complexes have been synthesized, with the aim to study the effect of the long alkoxy chain substituents on the mesogenic properties of the ligand and on the extent of electronic interaction between the two paramagnetic metal centers for binuclear Cu(II) complexes. The ligand and the complexes have been characterized by elemental analyses, IR, 1H NMR, and FAB mass and electronic spectral studies. Magnetic moment studies of the Cu (II) complexes show that there is antiferromagnetic spin-exchange interaction between the two Cu (II) centers through the phenyl bridge. The variable temperature magnetic studies show that the extent of spin-exchange interaction decreases with the increase in the length of the alkoxy side chain. The ligands 1,4-bis-(2-hydroxy-4-(n-alkoxy)benzaldimino)benzene exhibit liquid-crystalline properties with the smectic C phase. The mesogenic property of the ligand disappears on complex formation.

Synthesis and Ethylene Polymerization Activity of a Novel, Highly Active Single-Component Binuclear Neutral Nickel(II) Catalyst

The novel binuclear neutral nickel(II) complex [((2,6-iPr2C6H3)NCH)C6H3ONi(PPh3)Ph]2 (5), based on the 3,3‘-bisalicylaldimine ligand, has been synthesized in high yield, and its structure has been confirmed by X-ray crystallography, elemental analysis, and 1H NMR and 13C NMR spectra. Used in the polymerization of ethylene as an active single-component catalyst, the complex exhibited a high catalytic activity of up to 4.55 × 105 g of PE/((mol of Ni) h), and polyethylenes with a weight-average molecular weight (Mw) of up to 487.7 kg/mol and relatively broad molecular weight distribution (Mw/Mn = 2.8−3.8) were produced.

Macrocyclic binuclear copper(II) and nickel(II) complexes: the key role of central ions in hydrogen peroxide electrocatalysis

The electrochemistry of the macrocyclic dicopper(II) and dinickel(II) complexes [M 2 L]Cl 2 , where L is the [2+2] condensation product of 1,3-diaminopropane and 2,6-diformyl-4- tert -butylphenol, is reported in relation to hydrogen peroxide electrocatalysis on mercury. The opposite effects observed with [Cu 2 L]Cl 2 (inhibition) and [Ni 2 L]Cl 2 (enhancement) are explained by different reduction mechanisms.

New Tetraaza Macrobicyclic Ditopic Receptors for Metal Ions: Synthesis, Redox Response and Kinetics of Phosphate Hydrolysis of Unsymmetrical Macrobicyclic Mono- and Binuclear Nickel(II) Complexes

A new series of macrobicyclic ditopic receptors is derived from the precursor compound 3,4:10,11-dibenzo-1,13[N,N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}di-aza]-5,9-dioxocyclohexadecane. Using this precursor, mono- and binuclear nickel(II) complexes of type [NiL](ClO4) and [Ni2L](ClO4)2 have been synthesized to undertake electrochemical and catalytic studies on the basis of macrocyclic ring size. The receptor is a tricompartmental macrocycle consisting of ether oxygen, tertiary nitrogen and imine nitrogen atoms. The redox studies of these systems show that the nickel(II) complexes undergo quasi-reversible one-electron reduction and oxidation. All the nickel(II) complexes have square planar geometry and are EPR silent. Examination of the kinetics of the hydrolysis of 4-nitrophenyl phosphate shows that the catalytic activities of the complexes increase with the macrocyclic ring size of the complexes. As the macrocyclic ring size of the complexes increases, the spectral, electrochemical and catalytic studies of the complexes show considerable variation due to distortion in the geometry around the nickel(II) centre.

Synthesis and EPR Spectral Studies of Mono- and Binuclear Cobalt(II) and Nickel(II) Complexes with New 20‐Membered Dithiatetraazamacrocyclic [N4S2] Ligand

A new ligand, 6,10,16,20‐tetraketo‐8,18‐dithia‐1,5,11,15‐tetraazacycloeicosane [N4S2] (L), and its complexes with cobalt(II) and nickel(II), have been synthesized and characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, EPR and electronic spectral studies. The complexes were found to have the general composition [ML]X2 and [M2LX2]X2 for mono and binuclear complexes (M = Co, Ni; X = Cl, NO3, and SCN; and L = macrocyclic ligand). The mononuclear complexes of Co(II) and Ni(II) were found to have six‐coordinated octahedral geometry. However, the binuclear complexes of Co(II) and Ni(II) are square‐planar.

Synthesis, crystal structures and magnetic studies of terephthalato-bridged binuclear nickel(II) complexes

Two binuclear compounds [Ni 2(pmdtn) 2(tp)(H 2O) 2](ClO 4) 2(H 2O) 4 ( 1) and [Ni 2(pmdtn) 2(tp)(N 3) 2](H 2O) 4 ( 2) have been prepared by using the multibinding terephthalate (=tp) dianion and the tridentate capping ligand N, N, N ′, N ′, N″-pentamethyldiethyltriamine (=pmdtn) and have been characterized by X-ray crystallography and magnetic measurements. The crystal structures of both complexes show distorted octahedral geometries around the Ni(II) centers linked by the tp bridges in a bisbidentate fashion. The dihedral angles between the benzene rings and carboxylate groups correspond to 14.2° for 1 and 21.5° for 2. The intradimer distance of Ni⋯Ni through the tp ligand for 1 and 2 are 10.731 and 10.800 Å, respectively. The magnetic data reveal weak antiferromagnetic interactions transmitted by the tp bridge with J=−0.18 cm −1 ( 1) and −0.02 cm −1 ( 2), which is explained by the structural parameters.

Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

A series of N-(2-pyridyl)benzamides ( 1)–( 11) and their nickel complexes, [ N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide ( 12)–( 16) and (aryl)[ N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) ( 17)–( 24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12– 16/MAO systems is up to 3.3 × 10 4 g mol −1 h −1 whereas for 17– 24/MAO systems it is up to 4.94 × 10 5 g mol −1 atm −1 h −1. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh 3/Ni molar ratio on catalytic activity was investigated.

Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 4. New polydentate azomethine ligands based on 2,5-diformylpyrrole and 2,6-diformylpyridine

The reactions of 2,5-diformylpyrrole (1) and 2,6-diformylpyridine (2) with propane-1,3-diamine afforded new macrocyclic Schiff"s bases 5 and 6, respectively. Their structures were established by NMR spectroscopy and mass spectrometry. Binuclear copper(ii) and nickel(ii) complexes with ligand 5 were synthesized. Pentadentate Schiff"s base, viz., 2,6-bis[(2-aminophenylimino)methyl]pyridine, was prepared by demetallation of its complex with Cd(ClO4)2 using Na2S. In solutions, the latter Schiff"s base is quantitatively transformed into 2,6-bis(benzoimidazolyl)pyridine under the action of atmospheric oxygen or other mild oxidizing agents.

Synthesis, characterization and electrochemical behavior of mononuclear, binuclear nickel(II) and heterobinuclear zinc(II)nickel(II) complexes derived from novel macrobicyclic tricompartmental ligands: kinetics of the catalytic hydrolysis of 4-nitrophenyl phosphate by the complexes

Mononuclear, binuclear NiII and heterobinuclear ZnIINiII complexes have been derived from lateral macrobicyclic tricompartmental ligands embracing three different donor sets: (i) O2N2-donor set, derived from ether oxygens and tertiary amine nitrogens; (ii) N2O2-donor set, derived from tertiary amine nitrogens and phenolic oxygens; (iii) O2N2-donor set, derived from phenolic oxygens and azomethine nitrogens. Cyclic voltammograms of the mononuclear NiII complexes showed irreversible one-electron reduction processes in the −1.2 to −1.3 V region and an irreversible oxidation process in the range +0.8 V potential region. The binuclear complexes showed quasireversible two-step single electron reduction processes around the −1.3 and −1.7 V potential regions. The anodic potential region showed an irreversible oxidation process at +1.0 V. The heterobinuclear ZnIINiII complex showed an irreversible reduction of the NiII species at −1.55 V. The catalytic hydrolysis towards 4-nitrophenyl phosphate by the mononuclear, binuclear NiII complexes and the heterobinuclear complex were found to be appreciable. The pseudo-first order rate constant for the catalytic hydrolysis catalyzed by the binuclear and heterobinuclear complexes were found to be higher (9.8 × 10−4 s−1) than that of the corresponding mononuclear complexes (1.3 × 10−5 s−1), which ascertain the requirement of two metal ions in close proximity for the binding of the nucleophilic OH and the phosphate group.

Synthesis of unsymmetrical ‘end-off’ phenoxo and oximinato di bridged copper(II) and nickel(II) complexes: spectral, electrochemical and magnetic properties

New mononuclear and unsymmetrical binuclear copper(II) and nickel(II) complexes of the general formula [ML 1](ClO 4) · H 2O, [M 2L 1](ClO 4) 2 · 2H 2O, [ML 2](ClO 4) · H 2O and [M 2L 2](ClO 4) 2 · 2H 2O have been prepared by the condensation of 2-formyl-4-methyl-6-[(4-methylpiperazine-1yl)methyl]phenol ( 1) with N-β-aminoethyl isonitrosoethyl methyl ketimine(PCI) or N-β-aminomethylethyl isonitrosoethyl methyl ketimine(PCII) in the presence of M(II) salts (where M=Cu and Ni). The complexes were characterized by elemental and spectral analysis. Cyclic voltammetric studies evidenced one quasireversible reduction wave for all mononuclear complexes in the cathodic region. Two quasireversible one electron reduction waves are obtained for all binuclear complexes in the cathodic region. The binuclear copper(II) complexes illustrate an antiferromagnetic interaction ( μ eff: 1.55–1.58 BM) at 298 K with a broad EPR signal ( g=2.1). Variable temperature magnetic susceptibility study of the binuclear copper(II) complex [Cu 2L 1](ClO 4) 2 · 2H 2O ( 5) shows the observed −2 J value is 283 cm −1. The mononuclear copper(II) complexes have a magnetic moment value close to the spin only value with four hyperfine EPR signals.

Mixed-spin binuclear nickel(II) complexes in unsymmetrical ligand environments and related mononuclear compounds: electronic and molecular structures in solution and in the solid state.

Nickel(II) complexes of three new heterodonor ligands (HL(1), H(2)L(2), and H(3)L(3)) based on 2-aminocyclopent-1-ene-1-dithiocarboxylate have been synthesized, and their crystallographic characterizations are reported. With the pentacoordinating ligands HL(1) and H(3)L(3), the products obtained (1 and 2) are both mononuclear square planar compounds in which one of the pyrazolyl arms of ligand HL(1) and the bridgehead alkoxy oxygen of H(3)L(3) are staying away from coordination in 1 and 2, respectively. The saturated three carbon alkanyl chain in the ligand H(3)L(3) provides enough flexibility to generate tetrahedral distortion (dihedral angle, 22.7 degrees ) in the planarity of 2. Compound 1 displays paramagnetic line-broadening in its (1)H NMR spectrum due to oligomerization in solution. With the unsymmetrical binucleating ligand H(2)L(2), two mixed-spin homodinuclear complexes (3 and 4) have been synthesized using pyrazole and 2-mercaptopyridine as ancillary mu(2)-bridging ligands. Both these complexes have square planar low-spin and spin-triplet nickel(II) centers which display both coordination number and donor set asymmetry in tandem. The compounds have been characterized by (1)H NMR, electronic spectroscopy, and electrochemical studies.

Copper(II) and nickel(II) complexes of 5-methyl-2-hydroxyacetophenone N(4)-substituted thiosemicarbazones

Mononuclear and binuclear copper(II) and nickel(II) complexes with 5-methyl-2-hydroxyacetophenone N(4)-substituted thiosemicarbazones have been prepared and characterized. IR and 1H NMR spectra of the N(4)-substituted thiosemicarbazones and their metal complexes, as well as ESR spectra of the mononuclear copper(II) complexes, have been obtained. The crystal structures of 5-methyl-2-hydroxyacetophenone N(4)-dimethylthiosemicarbazone and a representative binuclear copper(II) complex have been acquired, and their structural features are compared to related thiosemicarbazones and previously reported binuclear copper(II) thiosemicarbazone complexes.

Mononuclear, dinuclear nickel(II) and heterodinuclear Zn(II)Ni(II) complexes as models for the active site of phosphatase

Mononuclear and dinuclear nickel(II) complexes and heterodinuclear Zn(II)Ni(II) complexes of the ligand 3,4:9,10-dibenzo-1,12-[ N, N ′bis{4-methyl-1-oxa)-6, 6 ′-formyl}-2-benzyldiaza]-5,8-dioxacyclotetradecane were prepared. The structure of the complex [NiL 1a] was solved by X-ray crystallography. The electrochemical reduction processes of the mononuclear nickel(II) and the heterobinuclear zinc(II)nickel(II) complexes were irreversible and that the binuclear nickel(II) complexes showed quasireversible reduction processes and irreversible oxidation processes. Kinetics of hydrolysis of 4-nitrophenyl phosphate catalyzed by the complexes showed pseudo first order processes with rate constants in the range 2 × 10 −5 s −1 for the mononuclear nickel(II) complexes and in the range 8 × 10 −4 s −1 for the homo binuclear nickel(II) and heterobinuclear zinc(II)nickel(II) complexes.