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.     

Ethylene Oligomerization Catalyzed by Nickel(II) Diimine Complexes

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Ethylene Oligomerization Catalyzed by Nickel（Ⅱ） Diimine Complexes

Ethylene oligomerization has been investigated by using catalyst systems composed of nickel(II) diimine complexes (diimine = N, N′‐o‐phenylene bis (salicylideneaminato), N, N′‐o‐phenylenebisbenzal, N, N′‐ethylenebisbenzal) and ethylaluminoxane (EAO). The main products in toluene and at 110–200 °C were olefins with low carbon numbers (C₄—C₁₀). Effects of reaction temperature, Al/Ni molar ratio and reaction period on both the catalytic activity and product distribution were explored. The activity of 1.84 × 10⁵ g of oligomer/(mol_NI · h), with 87.4% of selectivity to C₄—C₁₀ olefins, was attained at 200 °C in the reaction when a catalyst composed of NiCl₂ (PhCH = o‐NC₆H₄N = CHPh) and EAO was used.     

Alcoholate Complexes of Nickel(II) Chloride

Alcoholate complexes of nickel chloride with the general formula, NiCL₂ · ROH (R = CH₃, C₂H₅, i-C₃H₇, n-C₄H₉, t-C₄H₉, t-C₅H₁₁, n-C₆H₁₃ and n-C₈H₁₇), synthesized either by the reaction of anhydrous nickel chloride with alcohols or by the replacement of methanol from NiCL₂ · MeOH with higher alcohols, depict interesting differences when R is a secondary or tertiary alkyl group instead of a primary group. A study of the magnetic susceptibility, thermogravimetric measurement, electron spin resonance and electronic reflectance spectra has been carried out to throw light on the structure of these derivatives.     

Nickel Tetracarbonyl as Starting Material for the Synthesis of NHC-stabilized Nickel(II) Allyl Complexes

A novel, useful in situ synthesis for NHC nickel allyl halide complexes [Ni(NHC)(η³-allyl)(X)] starting from [Ni(CO)₄], NHC and allyl halides is presented. The reaction of [Ni(CO)₄] with (i) one equivalent of the corresponding NHC and (ii) with an excess of the corresponding allyl chloride at room temperature leads with elimination of carbon monoxide to complexes of the type [Ni(NHC)(η³-allyl)(X)]. This approach was used to synthesize the complexes [Ni(tBu₂Im)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 2 ), [Ni(iPr₂Im^Me)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 3 ), [Ni(iPr₂Im)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 4 ), [Ni(iPr₂Im)(η³-H₂C -C (H)-C (Me)₂)(Br)] ( 5 ), [Ni(Me₂Im^Me)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 6 ), and [Ni(EtiPrIm^Me)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 7 ). The complexes 1 to 7 were characterized using NMR and IR spectroscopy and elemental analysis, and the molecular structures are provided for 2 and 7 . The allyl nickel complexes 1 – 7 are stereochemically non-rigid in solution due to (i) NHC rotation about the nickel-carbon bond, (ii) allyl rotation about the Ni–η³-allyl axis and (iii) π–σ–π allyl isomerization processes. The allyl halide complexes can be methylated as was demonstrated by the methylation of a number of the complexes [Ni(NHC)(η³-allyl)(X)] with methylmagnesium chloride or methyllithium, which led to isolation of the complexes [Ni(Me₂Im)(η³-H₂C -C (Me)-C H₂)(Me)] ( 8 ), [Ni(tBu₂Im)(η³-H₂C -C (Me)-C H₂)(Me)] ( 9 ), [Ni(iPr₂Im^Me)(η³-H₂C -C (Me)-C H₂)(Me)] ( 10 ), [Ni(iPr₂Im)(η³-H₂C -C (Me)-C H₂)(Me)] ( 11 ), [Ni(iPr₂Im)(η³-H₂C -C (H)-C (Me)₂)(Me)] ( 12 ), and [Ni(EtiPrIm^Me)(η³-H₂C -C (Me)-C H₂)(Me)] ( 13 ). These complexes were fully characterized including X-ray molecular structures for 10 and 11 .     

Complexes of Nickel(II) Thiocyanate with Anilines

Complexes of the type NiL₂(SCN)₂ (L = aniline, o-, m-, p-toluidine, o-, m-, p-anisidine and p-phenetidine) have been prepared and characterised by room temperature magnetic moments and infra-red spectral data (down to 250 cm^?1) in the solid state. The thiocyanate is present as a bridging group and the metal atom is shown to be in a six-coordinate environment having an octahedral stereochemistry.     

Nickel(II) and Zinc(II) Complexes with Benzoylacetaldehyde Derivatives

Russian Journal of Coordination Chemistry - Ni(II) and Zn(II) complexes, [M(Ln)A] (n = 1–3, A = NH3, Py), were prepared from the products of condensation of benzoylacetaldehyde with aromatic...     

水杨醛亚胺镍配合物催化的乙烯水相聚合

在含表面活性剂的水相体系中, 用一系列水杨醛亚胺镍配合物催化乙烯聚合, 得到了高分子量低支化度聚乙烯. 研究表明水杨醛亚胺镍配合物中苯环上取代基的电子效应和空间位阻对乙烯聚合活性和聚合物的分子量有所影响. 提高配合物酚氧环上取代基的吸电子性, 聚合活性相应增加, 但聚乙烯的分子量降低; 而增加苯胺环上取代基的空间位阻, 聚合活性和聚乙烯的分子量均增加. 粘度法测得由水相聚合得到的聚乙烯的分子量在10⁴～10⁵范围内. DSC测得该聚乙烯的结晶度在50%～70%之间, 熔点在115～137 ℃范围内. GPC分析表明用环辛二烯合镍[Ni(COD)₂]助催化乙烯, 聚乙烯的分子量分布随酚氧环上取代基电负性增加而从双峰到单峰变化, 动态流变学研究进一步说明了聚乙烯分子量及其分布的变化.     

Copper(II) and Nickel(II) Complexes of `trans'-Difunctionalized Tetraaza Macrocycles

Reductive cleavage of the bis-aminal 1 of 1,4,8,11-tetraazacyclotetradecane allows a new synthesis of 1,8-dimethyl-1,4,8,11-tetraazacyclotetradecane ( 3 ), which is an ideal starting compound for preparing `trans'-difunctionalized derivatives. Thus, 3 was reacted to give the macrocyclic diacetonitrile 5 and dipropanenitrile 9 . These were reduced with Raney-Ni and H₂ to the corresponding diamines 6 and 10 , respectively. In addition, 5 was selectively hydrolysed to the diacetamide 7 and fully hydrolysed to the diacetic acid 8 . The Cu²⁺ and Ni²⁺ complexes of these new ligands were prepared and their spectral and structural properties studied. Whereas 3 yielded square planar species, the functionalized derivatives gave penta- or hexacoordinate complexes. The ligands with amino groups in their side chains ( 6 and 10 ) formed square planar species at acidic pH (amino groups protonated), but pentacoordinate geometries resulted at alkaline pH, where one amino group underwent coordination. In contrast, the diacetic acid 8 gave distorted octahedral Cu²⁺ and Ni²⁺ complexes.     

Dinuclear Nickel(II) Complexes as Models for the Active Site of Urease

Dinuclear nickel(II) complexes of the ligands 2,6-bis[bis((2-benzimidazolylmethyl)amino)methyl]-p-cresol (bbapOH), N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane (tbpOH), N-methyl-N,N',N'-tris(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane (m-tbpOH) and 1-[N,N-bis(2-benzimidazolylmethyl)amino]-3-[2-(3,5-dimethyl-1H-pyrazol-1-yl)ethoxy]-2-hydroxypropane (bpepOH) were prepared in order to model the active site of urease. The novel asymmetric structures of the dinuclear complexes were characterized by X-ray structure analysis. The complex [Ni(2)(bbapO)(ClO(4))(H(2)O)(MeOH)](ClO(4))(2).Et(2)O, 1, crystallizes in the monoclinic space group P2(1)/c, with a = 10.258(2) ?, b = 19.876(3) ?, c = 25.592(4) ?, and beta = 97.12(2) degrees. The nickel ions in 1 are bridged by the phenoxy donor of the ligand and a perchlorate anion. The complexes [Ni(2)(tbpO)(MeCOO)(H(2)O)](ClO(4))(2).H(2)O.Et(2)O, 2, [Ni(2)(m-tbpO)(PhCOO)(EtOH)(2)](ClO(4))(2).EtOH, 3, and [Ni(2)(bpepO)(MeCOO)(H(2)O)(2)](ClO(4))(2).H(2)O.Et(2)O.2EtOH, 4, also crystallize in the monoclinic crystal system with the following unit cell parameters: 2, C2/c, a = 35.360(13) ?, b = 10.958(3) ?, c = 24.821(10) ?, beta = 103.55(3) degrees; 3, Cc, a = 14.663(5) ?, b = 32.630(13) ?, c = 9.839(3) ?, beta = 92.49(2) degrees; 4, C2/c, a = 27.689(13) ?, b = 12.187(5) ?, c = 31.513(14) ?, beta = 115.01(3) degrees. The dinuclear centers of all these complexes are bridged by the alkoxy donor of the ligand and a carboxylate function. Compounds 2 and 3 have one of the nickel ions in a five-coordinated, trigonal bipyramidal coordination environment and thus show a high structural similarity to the dinuclear active site of urease from Klebsiella aerogenes. Furthermore, their magnetic and spectroscopic properties were determined and related to those of the urease enzymes. Activity toward hydrolysis of test substrates (4-nitrophenyl)urea, 4-nitroacetanilide, 4-nitrophenyl phosphate or bis(4-nitrophenyl) phosphate by the dinuclear complexes were examined by UV spectroscopic measurements.     

Neutral Nickel(II) and Copper(II) Tetraazamacrocyclic Complexes as Molecular Rods Attached to Gold Electrodes

New dithiolated derivatives of neutral Cu^II and Ni^II tetraazamacrocyclic complexes have been synthesized and characterized by spectroscopic and diffractional methods. These rod‐shaped molecules were assembled in monocomponent and mixed monolayers on gold electrodes. In the mixed monolayers, the active molecules were embedded in a hexanethiol matrix. The dithiolated complexes are oriented perpendicularly to the electrode, and reveal faster kinetics of electron transfer than those assembled in a single‐component monolayer. They appear as protrusions, which are easily addressed by using the STM method. In the presence of a suitable electron acceptor in the solution, the donor properties of the anchored Cu complex were weakened, which revealed donor–acceptor interactions with the monolayer. The peak position in the voltammogram indicates a stronger interaction of the solution‐based acceptor with the reduced Cu^II form than with the Cu^III complex. This suggests the possibility of switching the association on or off by applying an appropriate potential.     

Nickel(II) and Palladium(II) Bis(polychelate) Complexes as Promising Compounds for Piezoelectric Moisture Detectors

The interaction of binuclear nickel and palladium complexes with water vapor was studied by the piezoquartz microbalance technique. These compounds may be used as active coatings of threshold devices generating an analytical signal at low relative humidities.     

N-Formamid osalicylaldimine andN-Acetamidosalicylaldimine Complexes of Copper(II), Nickel(II) and Cobalt(II)

Summary N-formamidosalicylaldimine (H₂SF) andN-acetamidosalicylaldimine (H₂SA) complexes of Cu^II, Ni^II and Co^II have been synthesized and characterized by analytical, spectroscopic and magnetic data. The ligands coordinate to the metalvia the hydroxyl, carbonyl and imino groups to yield normal paramagnetic and insoluble complexes which decompose above 250°.     

Nickel(II) Complexes as Electron Transfer Mediators in the Electrochemical Activation of Freons

Feasibility was demonstrated for the electrochemical activation of freons CF₂ClCFCl₂ (CFC113), CF₃Br (FC13B1), and CF₂Cl₂ (CFC12) as well as CF₃I using nickel complexes with azamacrocyclic and bipyridyl ligands as electron transfer mediators, permitting the reduction of freons under mild conditions at relatively low potentials. The catalytic efficiency of these complexes was determined for freon CFC113.     

Silver(II) Complexes of Tetraazamacrocycles: Studies on e.p.r. and Electron Transfer Kinetics with Thiosulfate Ion

The e.p.r. studies of Ag^II complexes of three tetraazamacrocycles, 1,4,8,11-tetraazacyclo-tetradecane (cyclam)(I), 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-teradecane-4,11-diene (Me₆CD)(II) and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-teradecane (Me₆Cy)(III) and the electron transfer between [Ag^II(cyclam)]²⁺ and thiosulfate ion are described. The e.p.r. studies reveal that the spectra are almost the same as those reported earlier, particularly, for polycrystalline material and are typical of a d ⁹ planar Ag^II complexes. Previous e.p.r. studies on these square planar polycrystalline complexes showed no ligand hyperfine splitting. Reinvestigation of the e.p.r. spectra of these complexes in both the solid state and in solution at room (T 297 K) and at low (T= 120 K) temperature reveals resolved hyperfine structures in solution for [Ag(Me₆CD)]²⁺ and [Ag(Me₆Cy)]²⁺ complexes. Surprisingly, such a structure was not observed in solutions of [Ag(cyclam)]²⁺. Computer simulations of the hyperfine structure observed in solutions are in good agreement with structural formulae proposed. The oxidation of thiosulfate ion by [Ag(cyclam)]²⁺ follows the rate law:–d/dt[Ag^II(cyclam)²⁺]=(k ₁ Q ₁[H+]+k ₂ Q ₂ K _a2)/([H+]+K _a2)[Ag^II(cyclam)²⁺][S₂O₃ ^2–] and an inner-sphere mechanism is proposed, based on the spectral and kinetic evidence.     

Cobalt(II), Nickel(II), and Copper(II) Complexes with Diphenylthiocarbazide

New [ML(H₂O)₂] complexes (M = Co²⁺, Ni²⁺, or Cu²⁺; H₂L = diphenylthiocarbazide) were synthesized and studied using IR and diffuse reflection electronic spectroscopy, magnetic chemistry, conductometry, and DTA. The metals were shown to coordinate L^2–through nitrogen and sulfur atoms. The complex [CuL(H₂O)₂] is a dimer.     

Revisiting Alkane Hydroxylation with m-CPBA (m-Chloroperbenzoic Acid) Catalyzed by Nickel(II) Complexes

Mechanistic studies are performed on the alkane hydroxylation with m-CPBA (m-chloroperbenzoic acid) catalyzed by nickel(II) complexes, Ni^II(L). In the oxidation of cycloalkanes, Ni^II(TPA) acts as an efficient catalyst with a high yield and a high alcohol selectivity. In the oxidation of adamantane, the tertiary carbon is predominantly oxidized. The reaction rate shows first-order dependence on [substrate] and [Ni^II(L)] but is independent on [m-CPBA]; v_obs=k₂[substrate][Ni^II(L)]. The reaction exhibited a relatively large kinetic deuterium isotope effect (KIE) of 6.7, demonstrating that the hydrogen atom abstraction is involved in the rate-limiting step of the catalytic cycle. Furthermore, Ni^II(L) supported by related tetradentate ligands exhibit apparently different catalytic activity, suggesting contribution of the Ni^II(L) in the catalytic cycle. Based on the kinetic analysis and the significant effects of O₂ and CCl₄ on the product distribution pattern, possible contributions of (L)Ni^II−O^. and the aroyloxyl radical as the reactive oxidants are discussed.     

Nickel(II) Analogues of Phosphorescent Platinum(II) Complexes with Picosecond Excited-State Decay

Square-planar Ni^II complexes are interesting as cheaper and more sustainable alternatives to Pt^II luminophores widely used in lighting and photocatalysis. We investigated the excited-state behavior of two Ni^II complexes, which are isostructural with two luminescent Pt^II complexes. The initially excited singlet metal-to-ligand charge transfer (¹MLCT) excited states in the Ni^II complexes decay to metal-centered (³MC) excited states within less than 1 picosecond, followed by non-radiative relaxation of the ³MC states to the electronic ground state within 9–21 ps. This contrasts with the population of an emissive triplet ligand-centered (³LC) excited state upon excitation of the Pt^II analogues. Structural distortions of the Ni^II complexes are responsible for this discrepant behavior and lead to dark ³MC states far lower in energy than the luminescent ³LC states of Pt^II compounds. Our findings suggest that if these structural distortions could be restricted by more rigid coordination environments and stronger ligand fields, the excited-state relaxation in four-coordinate Ni^II complexes could be decelerated such that luminescent ³LC or ³MLCT excited states become accessible. These insights are relevant to make Ni^II fit for photophysical and photochemical applications that relied on Pt^II until now.     

Water-Soluble Polymeric Complexes of Cobalt(II) and Nickel(II) with Azolate Anions

N-Unsubstituted azoles (1,2,4-triazole, 3-amino-1,2,4-triazole) and 5-R-tetrazoles (R = H, CH₃, C₂H₅, C₄H₉, CH = CH₂, C₆H₅, p-CH₃C₆H₄, NH₂) form water-soluble polymeric complexes in systems containing certain transition metal salts. The data obtained and the results of MP2/6-31G^{* *} calculations of the electronic structures of 5-R-tetrazolate anions show that the ability of azoles for formation of polymeric complexes with transition metal ions is mostly determined by the acid-base properties of azoles. The geometric structure of a polymeric chain with the Co²⁺ ion having the coordination number 6 and the 5-methyltetrazolate anion being a bridging ligand was examined at the STO-3G level. It was shown that the coordination by the 2- and 3-nitrogen atoms of the tetrazole ring is most favored by energy.