[Ni(terpy)(H2O)]‐trans‐[Ni‐(μ‐CN)2‐(CN)2]n,a one‐dimensional linear tetra­cyano­nickelate chain

The one‐dimensional chain catena‐poly­[[aqua(2,2′:6′,2′′‐terpyridyl‐κ³N)­nickel(II)]‐μ‐cyano‐κ²N:C‐[bis­(cyano‐κC)nickelate(II)]‐μ‐cyano‐κ²C:N], [Ni(terpy)(H₂O)]‐trans‐[Ni‐μ‐(CN)₂‐(CN)₂]_n or [Ni₂­(CN)₄­(C₁₅H₁₁N₃)(H₂O)], consists of infinite linear chains along the crystallographic [10] direction. The chains are composed of two distinct types of nickel ions, paramagnetic octahedral [Ni(terpy)(H₂O)]²⁺ cations (with twofold crystallographic symmetry) and diamagnetic planar [Ni(CN)₄]^2? anions (with the Ni atom on an inversion center). The [Ni(CN)₄]^2? units act as bidentate ligands bridging through two trans cyano groups thus giving rise to a new example of a trans–trans chain among planar tetra­cyano­nickelate complexes. The coordination geometry of the planar nickel unit is typical of slightly distorted octahedral nickel(II) complexes, but for the [Ni(CN)₄]^2? units, the geometry deviates from a planar configuration due to steric interactions with the ter­pyridine ligands.     

A new one‐dimensional nickel metal–organic framework: catena‐poly[[[diaquabis(4‐{[(1‐phenyl‐1H‐tetrazol‐5‐yl)sulfanyl]methyl}benzoato‐κO)nickel(II)]‐μ‐4,4′‐bipyridine‐κ2N:N′] monohydrate]

The title complex, {[Ni(C₁₅H₁₁N₄O₂S)₂(C₁₀H₈N₂)(H₂O)₂]·H₂O}_n, was synthesized by the reaction of nickel chloride, 4‐{[(1‐phenyl‐1H‐tetrazol‐5‐yl)sulfanyl]methyl}benzoic acid (HL) and 4,4′‐bipyridine (bpy) under hydrothermal conditions. The asymmetric unit contains two half Ni^II ions, each located on an inversion centre, two L⁻ ligands, one bpy ligand, two coordinated water molecules and one unligated water molecule. Each Ni^II centre is six‐coordinated by two monodentate carboxylate O atoms from two different L⁻ ligands, two pyridine N atoms from two different bpy ligands and two terminal water molecules, displaying a nearly ideal octahedral geometry. The Ni^II ions are bridged by 4,4′‐bipyridine ligands to afford a linear array, with an Ni...Ni separation of 11.361 (1) Å, which is further decorated by two monodentate L⁻ ligands trans to each other, resulting in a one‐dimensional fishbone‐like chain structure. These one‐dimensional fishbone‐like chains are further linked by O—H...O, O—H...N and C—H...O hydrogen bonds and π–π stacking interactions to form a three‐dimensional supramolecular architecture. The thermal stability of the title complex was investigated via thermogravimetric analysis.     

Magnetic Exchange Interactions in Dinuclear Copper(II) and Nickel(II) Complexes with μ‐Oxalato Bridges. The Structure of μ‐Oxalato(O,O′, O″, O‴)‐bis{[1, 8‐di(2‐pyridyl)‐3, 6‐dithiaoctane‐N,N′, S,S′]nickel(II)} Dinitrate Dihydrate

A copper(II) and two nickel(II) dinuclear oxalato‐bridged compounds of formulae [{Cu(bpdto)}₂(μ‐ox)](ClO₄)₂ ( 1 ), [{Ni(bpdto)]₂(μ‐ox)](ClO₄)₂( 2 ), and [{Ni(bpdto)}₂(μ‐ox)](NO₃)₂·2H₂O ( 3 ), where bpdto = 1, 8‐bis(2‐pyridyl)‐3, 6‐dithiaoctane and ox = oxalate = C₂O₄^2— anion, have been synthesized and characterized. The crystal structure of 3 was determined by single‐crystal X‐ray analysis. It is a dinuclear complex with i symmetry in which the oxalate ligand is coordinated in bis(didentate) fashion to the inversion centre‐related nickel atoms. The distorted octahedral environment of each nickel atom is completed by two sulphur atoms in the equatorial plane and by two pyridyl nitrogen atoms in axial positions. Magnetic susceptibility measurements over the range 5 — 299K, show antiferromagnetic interactions that are weak in 1 (J = —12.8 cm^—1) and strong in 2 and 3 (J = —37.8 and —40.9 cm^—1, respectively), which in the case of 3 is in keeping with the observed structural parameters.     

Molecular Nonlinear Optical Properties of Acceptors Substituted 2,2′‐Bipyridine and 1,10‐Phenathroline Complexes of Nickel Dithiolate

Linear and nonlinear optical properties of two new nickel(diimine)(dithiolate) complexes, nickel(4,4′‐dinitro2,2′‐bipyridyl)(tfd), Ni(NO₂bipy)(tfd) , (tfd = 1,2‐trifluoromethylethene‐1,2‐dithiolate) and nickel(4,7‐diphenyl‐1,10‐phenathroline)(tfd), Ni(dpphen)(tfd) are reported. Ni(NO₂bipy)(tfd) has a potent electronic acceptor substituted on the diimine ligand and exhibits an enhanced molecular first hyperpolarizability (β₀ = ?31 × 10^?30 esu), which is more than three times greater than that (β₀ = ?10 × 10^?30 esu) of Ni(dpphen)(tfd). Ni(NO₂bipy)(tfd) also possesses the longest absorption wavelength, the largest solvatochromic shift, and one of the largest dipole moment changes (‐16 debye from ground to excited state) among nickel(diimine)(dithiolate) complexes. Crystal X‐ray structure of Ni(NO₂bipy)(tfd) is used to compared the π‐bonding structure of central (N=C‐C=N)Ni(S‐C=C‐S) unit with that of previously known nickel(4,4′‐bis(butyloxycarbonyl)‐2,2′‐bipyridyl)(tfd), Ni(CO₂Bubipy)(tfd).     

A 3D Nickel(II) Coordination Polymer with cds Nets Constructed from 3‐Pyridin‐4‐yl‐benzoic Acid

A new coordination polymer, [Ni(3,4‐pybz)₂(H₂O)]_n ( 1 ), was hydrothermally synthesized from Ni(NO₃)₂ · 6H₂O and an unsymmetrical 3‐pyridin‐4‐yl‐benzoic acid (3,4‐Hpybz). It was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and single‐crystal X‐ray diffraction. In complex 1 , the 3,4‐pybz ligands act as linear linkers to join 4‐connected nickel(II) ion nodes, to build a 3D 4‐connected twofold interpenetrated 6⁵8‐cds coordination framework. In addition, the magnetic and thermal properties of complex 1 were also investigated.     

Structural Insights into the Coordination and Extraction Mechanism of Nickel(II) with Dinonylnaphthalene Sulfonic Acid and n‐Hexyl 3‐Pyridinecarboxylate Ester as Extractants

In this work, a nickel(II) synergist complex with methyl isonicotinate (B^I, a short chain analog of n‐hexyl 3‐pyridinecarboxylate ester) and naphthalene‐2‐sulfonic acid (HNS, a short chain analog of dinonylnaphthalene sulfonic acid) was synthesized and studied by single‐crystal X‐ray diffraction. The nickel(II) complex crystallizes in the monoclinic P 2₁/n space group with the composition [Ni(H₂O)₄(B^I)₂](NS)₂·2H₂O. The Ni(II) ions of these crystallographically independent molecules lie on an inversion center, forming a trans‐form distorted octahedral coordination structure. The nickel(II) ions can coordinate with four water molecules and two B^I ligands, resulting in a mono‐metallic structure [Ni(H₂O)₄(B^I)₂]²⁺. There is no direct interaction between nickel(II) and sulfonic oxygen atoms of the sulfonate anions, but hydrogen bonds form between sulfonic oxygen atoms and water molecules in the synergist complex. In order to further elucidate the solution structure of the nickel(II) complexes with the actual synergistic mixture containing n‐hexyl 3‐pyridinecarboxylate ester and dinonylnaphthalene sulfonic acid in the nonpolar organic phase, the nickel(II) complexes were studied by electrospray ionization mass spectrometry. The results indicated that the extracted nickel(II) complexes in the nonpolar solvent have a similar coordination structure as that of the crystalline nickel(II) synergist complex.     

Highly branched and high‐molecular‐weight polyethylenes produced by 1‐[2,6‐bis(bis(4‐fluorophenyl)methyl)‐4‐MeOC6H2N]‐2‐aryliminoacenaphthylnickel(II) halides

A series of unsymmetrical 1‐[2,6‐bis(bis(4‐fluorophenyl)methyl)‐4‐MeOC₆H₂N]‐2‐aryliminoacenaphthene‐nickel(II) halides has been synthesized and fully characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (¹H NMR), ¹³C NMR, and ¹⁹F NMR spectroscopy as well as elemental analysis. The structures of Ni1 and Ni6 have been confirmed by the single‐crystal X‐ray diffraction. On activation with cocatalysts either ethylaluminum sesquichloride or methylaluminoxane, all the title nickel complexes display high activities toward ethylene polymerization up to 16.14 × 10⁶ g polyethylene (PE) mol^?1(Ni) h^?1 at 30 °C, affording PEs with both high branches (up to 103 branches/1000 carbons) and molecular weight (1.12 × 10⁶ g mol^?1) as well as narrow molecular weight distribution. High branching content of PE can be confirmed by high temperature ¹³C NMR spectroscopy and differential scanning calorimetry. In addition, the PE exhibited remarkable property of thermoplastic elastomers (TPEs) with high tensile strength (σ_b = 21.7 MPa) and elongation at break (ε_b = 937%) as well as elastic recovery (up to 85%), indicating a better alternative to commercial TPEs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 130–145     

Nickel(I)‐Komplexe mit 1,1′‐Bis(phosphino)ferrocenen als Liganden

Nickel(I) Complexes with 1,1′‐Bis(phosphino)ferrocenes as Ligands The thermically stable monomeric Nickel(I) complexes [(d^tbpf)Ni(acac)] ( 1 ) and [(dⁱppf)NiCl] ( 2 ) were synthesized and characterized by elemental analyses, EPR spectroscopy, and by X‐ray crystal structure analyses of single crystals (d^tbpf: 1,1′‐bis(di‐tertbutylphosphino)ferrocene; dⁱppf: 1,1′‐bis(diisopropylphosphino)ferrocene). 1 is formed by reduction of Ni(acac)₂ with triethylaluminium in the presence of d^tbpf, together with the nickel(0) complex [(d^tbpf)Ni(C₂H₄)]. 1 contains a Ni^I atom surrounded of two O‐ and two P donor atoms in a distorted tetrahedral coordination. 2 was obtained by reduction of [(dⁱppf)NiCl₂] with NaBH₄. In 2 the nickel(I) atom adopts trigonal planar coordination.     

Two 2,5‐bis(2‐pyridinyl)‐1,3,4‐oxa­diazo­le–metal complexes (M = Cu and Ni)

The reaction of the diazine ligand 3,5‐bis(2‐pyridinyl)‐1,3,4‐oxa­diazole (pod, C₁₂H₈N₄O), with Cu(CF₃SO₃)₂ or Ni(ClO₄)₂ afforded the title complexes di­aqua­bis­[3,5‐bis(2‐pyridinyl)‐1,3,4‐oxa­diazole‐N²,N³]copper(II) bis­(tri­fluoro­methane­sul­fon­ate), [Cu(pod)₂(H₂O)₂](CF₃SO₃)₂, and di­aqua­bis­[3,5‐bis(2‐pyridinyl)‐1,3,4‐oxa­diazo­le‐N²,N³]­nickel(II) diperchlorate, [Ni(pod)₂(H₂O)₂](ClO₄)₂. Both complexes present a crystallographically centrosymmetric mononuclear cation structure which consists of a six‐coordinated Cu^II or Ni^II ion with two pod mol­ecules acting as bidentate ligands and two axially coordinated water mol­ecules.     

Cyclische α,β-ungesättigte Carbonylverbindungen als Liganden in Nickel(0)-Komplexen

Cyclic α, β-Unsaturated Carbonyl Compounds as Ligands in Nickel (0) Complexes . As a result of the reaction of (Cy₃P)₂Ni(C₂H₄) with p-benzoquinone (p-CH) or maleic anhydride (MSA), nickel(II)-complexes of radical anions are formed which are derived from PCy₃ and p-CH or MSA by an equimolecular coupling. With other cyclic α, β-unsaturated carbonyl compounds (L = 1,4-naphthoquinone, substituted α- and γ-pyrones, substituted coumarins) no comparable reactions proceed in the coordination sphere of nickel(0) phosphine complexes. But depending on the phosphine and on the substrate compounds of the types (R₃P)₂NiL or (R₃P)NiL are obtained. Taking the substituted coumarins for an example, it was demonstrated that the latter type is favoured by bulky phosphines (PCy₃) and by coumarins with a high π-acceptor strength. The i.r. spectra of the complexes (R₃P)NiL are in accordance with an η³(C?C,O)-bridging function of α, β-unsaturated carbonyl ligands and therefore with an oligomeric structure. For the complexes (R₃P)₂NiL and (dipy)NiL an η²(C?C) or a pseudo-η³ (C?C,C) coordination of the ligands is discussed. Of special interest are the compounds (Cy₃P)Ni(DMP) and (Cy₃P)Ni(BDH) (DMP = 2, 6-dimethyl-γ-pyrone, BDH = 2-benzylidene-1, 3-dioxo-hydrindene). Possibly the substituted γ-pyrone is an η⁶-ligand in (Cy₃,P)Ni(DMP). (Cy₃,P)Ni(BDH) is considered to be a nickel(II) chelate of a diva-lent anion which is derived from BDH by the uptake of two electrons. In this connection the limits for a classification of the new complexes as nickel(0) or nickel(II) compounds are mentioned. The polarographic half-wave potentials are applied to an estimation of the reactivity of the α, β-unsaturated carbonyl compounds related to nickel(0) complexes.     

Adducts of nickel(II) acetylacetonate chelating with heterocyclic bases: 3‐­cyanopyridine and 4‐cyanopyridine

In both title compounds, (acetyl­acetonato‐O,O′)­bis(3‐cyano­pyridine‐N)­nickel(II), (I), and (acetyl­acetonato‐O,O′)­bis(4‐cyanopyridine‐N)­nickel(II), (II), both [Ni(C₅­H₇O₂)₂(C₆H₄N₂)₂], the Ni^II atom, which is situated on a centre of symmetry, is octahedrally coordinated. Distances and angles for (I) and (II), respectively, are: Ni—O 2.009 (2)/2.016 (2) and 2.0110 (16)/2.0238 (18) Å, Ni—N 2.116 (3) and 2.179 (2) Å, O—Ni—O 91.86 (10) and 90.19 (7)°, and O—Ni—N 91.27 (11)/90.19 (11) and 89.65 (8)/90.79 (7)°.     

Conformational Effects of [Ni2(μ‐ArS)2] Cores on Their Electrocatalytic Activity

Two nickel complexes supported by tridentate NS₂ ligands, [Ni₂(κ‐N,S,S,S′‐N^Ph{CH₂(MeC₆H₂R′)S}₂)₂] ( 1 ; R′=3,5‐(CF₃)₂C₆H₃) and [Ni₂(κ‐N,S,S,S′‐N^iBu{CH₂C₆H₄S}₂)₂] ( 2 ), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid‐state structure of 1 reveals that the [Ni₂(μ‐ArS)₂] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF₃COOH at ?1.93 (overpotential of 1.04 V, with i_cat/i_p≈21.8) and ?1.47 V (overpotential of 580 mV, with i_cat/i_p≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni₂(μ‐ArS)₂] core, which allows proximity of the two Ni???Ni centers at 2.730(8) Å; thus possibly favoring H⁺ reduction. In contrast, the planar [Ni₂(μ‐ArS)₂] core of 2 results in a Ni???Ni distance of 3.364(4) Å and is unstable in the presence of acid.     

Poly[[di‐μ2‐aqua‐di‐μ5‐croconato(2–)‐nickel(II)dipotassium(I)] tetra­hydrate]

In the title compound, {[K₂Ni(C₅O₅)₂(H₂O)₂]·4H₂O}_n, the Ni atom lies on an inversion centre. Two inversion‐related croconate [4,5‐dihydroxy‐4‐cyclo­pentene‐1,2,3‐trionate(2−)] ligands and an Ni^II ion form a near‐planar symmetrical [Ni(C₅O₅)₂]²⁻ moiety. The near‐square coordination centre of the moiety is then extended to an octa­hedral core by vertically bonding two water mol­ecules in the [Ni(C₅O₅)₂(H₂O)₂]²⁻ coordination anion. The crystal structure is characterized by a three‐dimensional network, involving strong K⋯O⋯K binding, K⋯O—Ni binding and hydrogen bonding.     

Four NiII complexes with the new cyclam–methylimidazole ligand 1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane

Although it has not proved possible to crystallize the newly prepared cyclam–methylimidazole ligand 1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane (L^Im1), the trans and cis isomers of an Ni^II complex, namely trans‐aqua{1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}nickel(II) bis(perchlorate) monohydrate, [Ni(C₁₅H₃₀N₆)(H₂O)](ClO₄)₂·H₂O, (1), and cis‐aqua{1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}nickel(II) bis(perchlorate), [Ni(C₁₅H₃₀N₆)(H₂O)](ClO₄)₂, (2), have been prepared and structurally characterized. At different stages of the crystallization and thermal treatment from which (1) and (2) were obtained, a further two compounds were isolated in crystalline form and their structures also analysed, namely trans‐{1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}(perchlorato)nickel(II) perchlorate, [Ni(ClO₄)(C₁₅H₃₀N₆)]ClO₄, (3), and cis‐{1,8‐bis[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}nickel(II) bis(perchlorate) 0.24‐hydrate, [Ni(C₂₀H₃₆N₆)](ClO₄)₂·0.24H₂O, (4); the 1,8‐bis[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane ligand is a minor side product, probably formed in trace amounts in the synthesis of L^Im1. The configurations of the cyclam macrocycles in the complexes have been analysed and the structures are compared with analogues from the literature.     

Bis­[1‐(p‐chloro­phenyl)‐5‐iso­propyl­biguanide‐κ2N2,N4]­nickel(II) dichloride di­methyl­form­amide solvate

The asymmetric unit of the title compound, [Ni(C₁₁H₁₆ClN₅)₂]Cl₂·C₃H₇NO, contains one monomeric nickel(II) com­plex cation, two Cl⁻ anions and one di­methyl­form­amide sol­vent mol­ecule. The Ni atom is coordinated to each of two 1‐­(p‐chloro­phenyl)‐5‐iso­propyl­biguanide (proguanil) ligands via two N atoms. The complex exhibits a square‐planar coordination, with the Ni atom lying 0.021 (2) Å out of the basal plane. The crystal packing is characterized by several hydrogen bonds.     

Poly­[[μ2‐aqua‐bis­[(1,10‐phenanthro­line)nickel(II)]]‐di‐μ2,μ4‐5‐nitro‐1,3‐benzene­di­carboxyl­ato]

The reaction of Ni(CH₃COO)₂·4H₂O, 5‐nitro‐1,3‐benzene­di­carboxylic acid (H₂nmbdc), 1,10‐phenanthroline and water under hydro­thermal conditions yields the first reported two‐dimensional nickel coordination polymer with water‐ and carboxyl­ate‐bridged dimeric units, viz. [Ni₂(C₈H₃NO₆)₂(C₁₂H₈N₂)₂(H₂O)]_n. The coordination polyhedron of the Ni^II ion in the title structure is an octahedron defined by an N₂O₄ donor set. The water mol­ecule is positioned on a mirror plane and the 5‐nitro‐1,3‐benzene­di­carboxylate group is located on a twofold axis. Two types of nmbdc²⁻ coordination mode are observed: one is a bis‐monodentate mode, μ₂‐nmbdc²⁻, and the other is a bis‐bridging mode, μ₄‐nmbdc²⁻. The dimeric unit in the title compound is similar to the structural moiety in urease. In the two‐dimensional framework in the title compound, strong stacking interactions between benzene rings (μ₂‐nmbdc²⁻ and μ₄‐nmbdc²⁻) and 1,10‐phenanthroline ligands are observed.     

Bis­(di‐μ‐acetato‐aqua{2‐[N‐ethyl‐N‐(2‐hydroxy‐4‐methyl­benzyl)­amino­methyl]‐1‐methyl­benz­imid­az­ole}­nickel)­nickel(II) tetra­hy­drate

The previously unknown title compound, tetra‐μ‐ace­tato‐1:2κ²O;1:2κ²O:O′;­2:3κ²O;­2:3κ²O:O′‐di­aqua‐1κO,3κO‐bis­(μ‐2‐{[N‐ethyl‐N‐(2‐hy­droxy‐5‐methylbenzyl)­am­ino]­methyl}‐1‐methyl‐1H‐benz­imid­az­ole)‐1κ³N³,N,O:2κO;3κ³N³,N,O:2κO‐tri­nickel(II) tetra­hy­drate, [Ni₃(C₁₈H₂₂N₃O)₂(C₂H₃O₂)₄(H₂O)₂]·­4H₂O, (I), is a centrosymmetric linear trinuclear nickel(II) complex, where the Ni atoms are in an octahedral coordination and the ligand heteroatoms act so as to model amino acid residues.     

A Mononuclear η2‐Bonded Phosphaalkyne Nickel(0) Complex

The synthesis and characterization of the new complex [Ni(Im^iPr)₂(η²‐P≡C‐tBu)] ( 1 ) is reported. Compound 1 represents the first structurally characterized example of a mononuclear nickel(0) complex with a side on coordinated phophaalkyne ligand.     

[N,N′‐Bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminato]­nickel(II) and [N,N′‐bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminato]copper(II)

In the title compounds, {2,2′‐[2,2‐di­methyl‐1,3‐propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴N,N′,O,O′}nickel(II), [Ni(C₁₉H₂₀N₂O₂)], and {2,2′‐[2,2‐di­methyl‐1,3‐propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴N,N′,O,O′}copper(II), [Cu(C₁₉H₂₀N₂O₂)], the Ni^II and Cu^II atoms are coordinated by two iminic N and two phenolic O atoms of the N,N′‐bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminate (SALPD^2?, C₁₇H₁₆N₂O₂^2?) ligand. The geometry of the coordination sphere is planar in the case of the Ni^II complex and distorted towards tetrahedral for the Cu^II complex. Both complexes have a cis configuration imposed by the chelate ligand. The dihedral angles between the N/Ni/O and N/Cu/O coordination planes are 17.20 (6) and 35.13 (7)°, respectively.     

Synthesis of 2‐(N‐arylimino)pyrrolide nickel complexes and polymerization of methyl methacrylate

The synthesis, characterization and methyl methacrylate polymerization behaviors of 2‐(N‐arylimino)pyrrolide nickel complexes are described. The nickel complex [NN]₂Ni ( 1 , [NN] = [2‐C(H)NAr‐5‐tBu‐C₄H₂N]^?, Ar = 2,6‐iPr₂C₆H₃) was prepared in good yield by the reaction of [NN]Li with trans‐[Ni(Cl)(Ph)(PPh₃)₂] in THF. Reaction of [NN]Li with NiBr₂(DME) yielded the nickel bromide [NN]Ni(Br)[NNH] ( 2 ). Complexes 1 and 2 were characterized by ¹H NMR and IR spectroscopy and elemental analysis, and by X‐ray single crystal analysis. Both complexes, upon activation with methylaluminoxane, are highly active for the polymerization of methyl methacrylate to give high molecular weight polymethylmethacrylate with narrow molecular distributions. Copyright © 2009 John Wiley & Sons, Ltd.