N-(5,6,7-trihydroquinolin-8-ylidene)-2-benzhydrylbenzenaminonickel halide complexes: synthesis, characterization and catalytic behavior towards ethylene polymerization

A series of N-(5,6,7-trihydroquinolinylidene)-2-benzhydrylbenzenamine ligands was synthesized and characterized by (1)H/(13)C NMR and IR spectroscopy, and by elemental analysis. These ligands reacted with NiCl(2) or NiBr(2)(DME) to form the title halide complexes, which were also characterized by IR spectroscopy and elemental analysis. Single crystal X-ray diffraction revealed that the representative nickel complexes crystallized as centro-symmetric dimers with chloro-bridges linking distorted octahedral nickel centers. On activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et(2)AlCl), all nickel pre-catalysts showed high activities for ethylene polymerization, producing polyethylene with narrow molecular weight distribution, consistent with single-site catalysis. The nature of the ligands and reaction parameters were investigated and discussed in terms of their influence on the catalytic behavior of these nickel pre-catalysts.     

The synthesis, coordination chemistry and ethylene polymerisation activity of ferrocenediyl nitrogen-substituted ligands and their metal complexes

Treatment of aminoferrocene with substituted 2-hydroxybenzaldehydes yields the air- and moisture-stable ligands 1–4, which were then reacted to form the chromium dichloride complexes 5–7 and the nickel bis-chelate species 8 and 9. The metal compounds are very air-sensitive but the chromium compounds act as pre-catalysts for the polymerisation of ethylene. Reaction of 1,1′-bis(amino)ferrocene with similarly substituted 2-hydroxybenzaldehyes or simple benzaldehyde gives the ligands 10–12 and 17, respectively. The X-ray crystal structure of 11 shows the molecule to have non-crystallographic C₂ symmetry and to be linked by C–Hπ interactions between the anthracene rings. Titanium-containing complexes 13–16 can be formed utilising ligands 10–12 and there is a change in geometry within the complexes dependent on the adjacent co-ligands, whilst ligand 17 can be reacted with PdClMe(COD) to form the chelate complex 18. Cyclic voltammetric studies have been carried out on 18 and its oxidised analogue 19, but both complexes are inactive towards ethylene polymerisation.     

Synthetic and Structural Studies of N-Heterocyclic Carbene Complexes of Nickel

Transition metal complexes of stable N-heterocyclic carbenes have recently gained increasing attention as pre-catalysts for a number of important reactions primarily based on the analogy between N-heterocyclic carbenes and strong ó-donating tertiary phosphines,[1] Although a large number of transition-metal carbene complexes have been reported, very few incorporate chelating carbenes were reported.[2,3] Therefore, we have set out to prepare and study transition-metal compounds with chelating di-N-heterocyclic carbenes, and we now report new dicationic tetra(carbine)nickel(Ⅱ) complexes in this class (Scheme 1). Their structures have been determined by single-crystal X-ray diffraction studies (Figure 1).     

2-Benzoimidazol-8-alkylquinolinylnickel(II) complexes as efficient catalysts for ethylene oligomerization and vinyl polymerization of norbornene

A series of nickel complexes LNiCl₂ (C1–C16), where L represents 2-benzoimidazol-8-alkylquinoline and its derivatives, were prepared as potential catalysts for the oligomerization of ethylene. The molecular structure of a representative complex C2·CH₃CH₂OH was determined by single-crystal X-ray diffraction. Upon treatment with diethylaluminium chloride (Et₂AlCl), all nickel complex pre-catalysts exhibited good activities in the oligomerization of ethylene. Furthermore, in the presence of methylaluminoxane (MAO), the nickel pre-catalysts were suitable for vinyl polymerization of norbornene.     

EPR study of (η5-cyclopentadienyl)nickel(I) complexes with P-and N-Donor ligands and 1,5-cyclooctadiene

Mononuclear (η⁵-cyclopentadienyl)nickel(I) complexes with triphenylphosphine, triethylphosphite, 2,2’-bipyridyl, and 1,5-cyclooctadiene formed in the course of reduction of nickelocene were studied by EPR method. Monocyclopentadienyl Ni(I) complexes of the composition CpNiL₂ were shown to form during nickelocene reduction irrespective of the method applied (the use of organometallic compound, alkali metal, thermal conditions) in the presence of stabilizing ligands L (L = PPh₃, P(OEt)₃, Bipy/2, COD/2) and in the course of contradisproportionation reaction between nickelocene and the corresponding NiL₄ complex. It was found that in the structure of these CpNiL₂ complexes (L = PPh₃, P(OEt)₃, Bipy/2), the main molecular axis is perpendicular to the L-Ni-L plane and these complexes should be considered as derivatives of trigonal structures of D _3h symmetry distorted by Cp ligand. In CpNi(COD) complex, the main axis passes through the Cpring center and this complex should be treated as a derivative of pentagonal structure of C _5v symmetry distorted by COD ligand. Nonequivalence of ³¹P nuclei results from vibronic interaction effect in tricoordinate structures in pseudodegenerate electron state (Jahn-Teller effect).     

Wechselwirkungen zwischen Hetero-π-Systemen und Zentralmetallen niedriger Oxydationsstufen: Stöchiometrische Verknüpfungsreaktionen von Azomethinen und 1,3-Dienen am Nickel(0)

Interactions between Hetero-π-Systems and Central Metals in Low Oxidation States: Stoichiometric Reactions of Azomethines and 1,3-Dienes with Nickel(0) Azomethines and 1,3-Dienes react with Ni(COD)₂ under oxydative coupling to form different types of organo nickel(II) compounds. The route of this reactions depends on the nature of the azomethines and dienes and can be controlled by kinetic and thermodynamic parameters. The new complexes are investigated by IR, MS, and H-NMR measurements. The reaction of cinnamaldehydanil and dienes with Ni(COD)₂ gives a binuclear complex. X-ray analysis shows that 2 C₇N-chains are bonded to 2 Nickel(II) central atoms.     

Influence of a diimine ligand and an activator on the processes taking place in Brookhart-type nickel catalytic systems

Research on Chemical Intermediates - Brookhart-type catalytic systems based on zero-valent nickel complexes Ni(COD)2 and Ni(COD)L [where COD is cyclooctadiene and L is...     

Ligand-redox assisted nickel catalysis toward stereoselective synthesis of (n+1)-membered cycloalkanes from 1,n-diols with methyl ketones

A well-defined, bench-stable nickel catalyst is presented here, that can facilitate double alkylation of a methyl ketone to realize a wide variety of cycloalkanes. The performance of the catalyst depends on the ligand redox process comprising an azo-hydrazo couple. The source of the bis electrophile in this double alkylation is a 1,n-diol, so that (n+1)-membered cycloalkanes can be furnished in a stereoselective manner. The reaction follows a cascade of dehydrogenation/hydrogenation reactions and adopts a borrowing hydrogen (BH) method. A thorough mechanistic analysis including the interception of key radical intermediates and DFT calculations supports the ligand radical-mediated dehydrogenation and hydrogenation reactions, which is quite rare in BH chemistry. In particular, this radical-promoted hydrogenation is distinctly different from conventional hydrogenations involving a metal hydride and complementary to the ubiquitous two-electron driven dehydrogenation/hydrogenation reactions.

A homogeneous nickel catalyst is described that forms (n+1)-membered cycloalkane rings from ketones and 1,n-diols following a radical-promoted pathway.     

Copper(II), nickel(II) and cobalt(II) complexes of oxaldihydrazide and succindihydrazide Schiff bases with salicylaldehyde ando-hydroxyacetophenone

Summary Polymeric copper(II), nickel(II) and cobalt(II) complexes of the type M₂L where M = Cu^II, Ni^II or Co^II and H₄L = disalicylaldimine oxamide (H₄A), di(o-hydroxyacetophenoneimine)oxamide (H₄B), disalicylaldimine succinamide (H₄C) or di(o-hydroxyacetophenoneimine)succinamide (H₄D), have been synthesized and characterized by analysis, i.r. and electronic spectra and magnetic moment data. Copper(II) complexes and some of the nickel(II) and cobalt(II) complexes are planar while other nickel(II) complexes are distorted octahedral and other cobalt(H) complexes are square pyramidal. Anomalously low magnetic moments of some complexes have been related to M-M interactionsvia oxo-bridge structures.     

Which Stereoinductor Is Better for Asymmetric Functionalization of α-Amino Acids in a Nickel(II) Coordination Environment? Experimental and DFT Considerations

The results of extended comparative investigation of nickel(II) Schiff base complexes (containing various auxiliary chiral moieties) commonly used as a methodological platform for the asymmetric synthesis of tailor-made α-amino acids are provided. The following issues are addressed: 1) redox activity (determining the possibility for electrochemically induced reactions); 2) quantitative estimation of the reactivity of deprotonated complexes towards electrophiles; and 3) quantum-chemical estimation of noncovalent interactions in the metal coordination environment (which shed light on the origin of the stereochemical outcome observed for different stereoinductors). Possible mechanisms that determine the relationship between the stereochemical configuration of a molecule and its electronic structure are discussed. The DFT-calculated HOMO–LUMO energies and localization, as well as relative energies for the (S)- and (R)-alanine derivatives, that determine the stereoinduction efficiency in thermodynamically controlled reactions in nickel(II) coordination are provided. The computational data are supported by experimental results on the monobenzylation of glycine derivatives.     

Synthesis,characterization and ethylene polymerization of 1-(2,6-dimethyl-4-fluorenylphenylimino)-2-aryliminoacenaphthylnickel bromides

A series of 1-(2,6-dimethyl-4-fluorenylphenylimino)-2-aryliminoacenaphthylene compounds (aryl = 2,6-di(Me)Ph (L1), 2,6-di(Et)Ph (L2), 2,6-di(i-Pr)Ph (L3), 2,4,6-tri(Me)Ph (L4), 2,6-di(Et)-4-MePh (L5)) was prepared and used to form their corresponding dibromonickel complexes (D1–D5). Both L1–L5 and D1–D5 were fully characterized by FT-IR and elemental analysis as well as NMR measurements in the case of ligands L1–L5. The molecular structure of the representative complex D5 was confirmed by single crystal X-ray diffraction revealing a distorted trigonal bipyramidal geometry around the nickel center. On activation with either ethylaluminium sesquichloride (Et₃Al₂Cl₃, EASC) or methylaluminoxane (MAO), all nickel complexes exhibited high activities up to 9.82 × 10⁶ g of PE (mol of Ni)⁻¹ h⁻¹ for ethylene polymerization. In comparison with the polyethylenes obtained with related Ni pre-catalysts, the polyethylenes obtained in this work possessed relatively higher molecular weights and lower levels of branching, highlighting the significant influence of the remote fluorenyl substituent.     

Crystal Structure and Magnetic Properties of Copper(II) and Nickel(II) Binuclear Complexes with Bisacylhydrazones Based on 2,6‐Diformyl‐4‐methylphenol

The series of binuclear Cu(II) and Ni(II) complexes with an asymmetrical exchange fragment based on 2,6‐diformyl‐4‐methylphenol bishydrazone has been synthesized for the first time. The compositions and structures of both ligands and its complexes have been established with the data of IR, ¹H NMR, and extended X‐ray absorption fine structure (EXAFS) spectroscopical studies as well as magnetic measurements. The structure of [Ni₂L₃(μ‐Pz)] · 2CH₃OH (L = triply deprotonated form of bishydrazone, Pz = pyrazol) was confirmed by X‐ray crystallographic analysis. In this complex, the coordination environment of two nickel ions is quite different, one nickel atom is square‐planar and the other is distorted octahedral coordinated. The values of exchange parameter calculated in terms of HDVV theory have been compared with the features of an asymmetrical exchange fragment's electronic and geometrical structure.     

Chiral and Achiral Bis（2-oxazolinylphenolato）nickel（Ⅱ） Complexes-Synthesis, Crystal Structure, and Catalytic Properties

Introduction Oxidation was a very important reaction both in synthetic pathways and in industrial processes. Metal-catalyzed oxidation provided excellent alternatives in synthetic processes. However, molecular oxygen has been applied only in a limited number of metal-catalyzed oxidations, because it was very difficult to activate molecular oxygen and most of transition metal complexes were sensitive to oxygen. It was noted that metal-catalyzed Baeyer-Villiger oxidation was a convenient method…     

Solid-supported cross-coupling catalysts derived from homogeneous nickel and palladium coordination complexes

Solid-supported catalysts derived from homogeneous nickel(II) and palladium(II) non-symmetrical salen-type coordination complexes have been prepared and shown to be effective in the heterogeneous catalysis of carbon-carbon cross-coupling reactions. The nickel catalyst has been used in room-temperature Tamao-Kumada-Corriu reactions and the palladium catalyst in the Heck reaction at elevated temperatures. The complexes were prepared by improved methods and characterised by spectroscopic techniques. Comparisons between the solid-supported catalysts and their homogeneous analogues are reported. The single-crystal structure determination of the nickel and palladium complexes [M(salenac-OH)][M = Ni, Pd; salenac-OH = 9-(2',4'-dihydroxyphenyl)-5,8-diaza-4-methylnona-2,4,8-trienato](2-)] is reported.     

Rhodium and platinum complexes as catalysts for the polymerization of phenylacetylene

In polymerization reactions of phenylacetylene three different types of polyphenylacetylene (PPA) were prepared by using Rh and Pt complexes as catalysts in different reaction conditions. Type I PPA is obtained with [Rh (COD) Chel] PF₆ complexes (COD = cis,cis-cycloocta 1,5-diene; chel = 2,2′-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline) in bulk, benzene methanol, while type II PPA is obtained with the same catalysts in p-dioxane and type III PPA in the presence of [Pt (? C?CPh)₂(PPh₃)₂] in bulk. Type I, II, and III PPA exhibit different IR and ¹H-NMR spectra, which have been compared with literature data. Correlations proposed by different Authors between spectral properties of PPA and chain structures are also discussed.     

Synthesis and electrochemical characterization of complexes of 1,2-bis[2-(pyridylmethylideneamino)phenylthio]ethanes with transition metals (CoII, NiII, CuII)

Transition metal (Ni^II, Co^II, and Cu^II) complexes with 1,2-bis[2-(3-pyridylmethylideneamino)phenylthio]ethane (1) and 1,2-bis[2-(4-pyridylmethylideneamino)phenylthio]ethane (2) were synthesized for the first time by slow diffusion of solutions of compounds 1 or 2 in CH₂Cl₂ into solutions of MX₂ · nH₂O (M = Ni, Co, or Cu; X = Cl or NO₃; n = 2 or 6) in ethanol. The reactions with Co^II and Cu^II chlorides afford complexes of composition M(L)Cl₂ (L = 1 or 2). The reactions of compound 1 with Ni^II salts produce complexes with 1,2-bis(2-aminophenylthio)ethane. The molecular structure of dinitrato[1,2-bis(2-aminophenylthio)ethane]nickel(ii) was confirmed by X-ray diffraction. The ligands and the complexes were investigated by cyclic voltammetry and rotating disk electrode voltammetry. The initial reduction of the complexes proceeds at the metal atom. The oxidation of the chlorine-containing complexes proceeds at the coordinated chloride anion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 350–355, February, 2008.     

8-Oxyquinolate iridium(I) complexes and their oxidative-addition reactions

The novel sixteen-electron complex [Ir(Oq)(COD)] (Oq = 8-oxyquinolate; COD = 1,5-cyclooctadiene) adds monodentate phosphines, phosphites or activated olefins irreversibly to give pentacoordinate iridium(I) complexes of the type [Ir(Oq)(COD)L] (L = PPh₃, P(OPh)₃, maleic anhydride or tetracyano-ethylene). Reaction of [Ir(Oq)(COD)] with some diphosphines leads to substitution products of the general formula [Ir(Oq)(diphos)] (diphos = 1,2-bis(diphenylphosphino)ethane or cis-1,2-bis(diphenylphosphino)ethylene). Carbon monoxide displaces the COD group from the complexes giving either [Ir(Oq)(CO)₂] or [Ir(Oq)(CO)L], and the latter undergo oxidative addition reactions with SnCl₄, Me₃SiCl, Me₃SnCl, MeI, allylbromide, PhCOCl, MeCOCl, Cl₂, Br₂, TlCl₃ and HCl leading to novel iridium(III) complexes.     

Preparation,characterization and antifungal properties of nickel(II) complexes of tridentate ONS ligands derived from N-methyl-S-methyldithiocarbazate and the X-ray crystal structure of the [Ni(ONMeS)CN]·H2O complex

Nickel(II) complexes of general empirical formula, NiLX·nH₂O (L = deprotonated form of the Schiff base formed by condensation of N-methyl-S-methyldithiocarbazate with 2-hydroxybenzaldehyde or 5-bromo-2-hydroxybenzaldehyde; X = Cl^–, Br^–, NCS^–, AcO^– or CN^–; n = 0, 1) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a square-planar structure for these complexes. The crystal structure of the [Ni(ONMeS)CN]·H₂O complex (ONMeS = anionic form of the 2-hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the Schiff base is coordinated to the nickel(II) ion as a uninegatively charged anion coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth coordination position is occupied by a cayano ligand. The antifungal properties of the Schiff bases and their nickel(II) complexes were studied against three plant pathogenic fungi. The ligands display moderate fungitoxicities against these organisms but their nickel(II) complexes are less active than the free ligands.     

α‐Diamine Nickel Catalysts with Nonplanar Chelate Rings for Ethylene Polymerization

A series of novel α‐diamine nickel complexes, (ArNH‐C(Me)‐(Me)C‐NHAr)NiBr₂, 1 : Ar=2,6‐diisopropylphenyl, 2 : Ar=2,6‐dimethylphenyl, 3 : Ar=phenyl), have been synthesized and characterized. X‐ray crystallographic analysis showed that the coordination geometry of the α‐diamine nickel complexes is markedly different from conventional α‐diimine nickel complexes, and that the chelate ring (N‐C‐C‐N‐Ni) of the α‐diamine nickel complex is significantly distorted. The α‐diamine nickel catalysts also display different steric effects on ethylene polymerization in comparison to the α‐diimine nickel catalyst. Increasing the steric hindrance of the α‐diamine ligand by substitution of the o‐methyl groups with o‐isopropyl groups leads to decreased polymerization activity and molecular weight; however, catalyst thermal stability is significantly enhanced. Living polymerizations of ethylene can be successfully achieved using 1 /Et₂AlCl at 35 °C or 2 /Et₂AlCl at 0 °C. The bulky α‐diamine nickel catalyst 1 with isopropyl substituents can additionally be used to control the branching topology of the obtained polyethylene at the same level of branching density by tuning the reaction temperature and ethylene pressure.     

Cover Picture: Coordination Algorithms Control Molecular Architecture: [CuI4(L2)4]4+ Grid Complex Versus [MII2(L2)2X4]y+ Side‐By‐Side Complexes (M=Mn,Co, Ni,Zn; X=Solvent or Anion) and [FeII(L2)3][Cl3FeIIIOFeIIICl3] (Chem. Eur. J. 16/2003)

The cover picture shows how differing coordination algorithms control the molecular architecture of complexes of the pyridazine‐containing, two‐armed, acyclic Schiff base ligand L2 (left, prepared from one equivalent of 3,6‐diformylpyridazine and two equivalents of d‐anisidine). Two very different complexes of L2 self‐assemble from tetrahedral copper(I ) versus octahedral zinc(II ), nickel(II ), and cobalt(II ) controlled 1 : 1 reactions with L2. In both cases the metal ions are bridged by the pyridazine moieties in L2, but in the case of the tetrahedral copper(II ) the result is a tetrametallic [2×2] grid complex ([Cu^I₄(L2)⁴]⁴⁺: top right), whilst in the case of the octahedral metal(II ) ions dimetallic side‐by‐side complexes, [M^II₂(L2)²(X)₄]^y+ (M = Mn, Co, Ni, Zn; X = solvent or anion), are formed (bottom right). The cover image was kindly generated by M. Crawford (University of Otago) with Strata Studio Pro (Strata). More details are given by S. Brooker and co‐workers on p. 3772 ff.