Nickel Chemistry Research Articles

Boosting N-Heterocyclic Carbene Radical Organocatalysis with Nickel Chemistry: A Rational Mechanistic Study-Based Approach

Boosting <i>N</i>-Heterocyclic Carbene Radical Organocatalysis with Nickel Chemistry: A Rational Mechanistic Study-Based Approach

Nickel Metallaphotoredox Buchwald–Hartwig Amination Reactions: A Perspective on Irradiation Light Wavelength

AbstractThe construction of C−N bonds is considered one of the most useful reactions in synthetic chemistry due to their widespread presence in pharmaceuticals, natural products, etc. Pd‐catalyzed Buchwald–Hartwig amination (BHA) has provided the most efficient method to form (hetero)aryl amines but it required strong base and sophisticated ligands. In comparison, the combination of photocatalysis and nickel chemistry has revolutionized catalytic strategies and is emerging as a quintessence to realize BHA, termed as Ni‐metallaphotoredox BHA. To pursue a universal protocol, diverse photocatalysts were designed and employed in Ni‐metallaphotoredox BHA, and smoothly promoted C−N bond formations under irradiation of light from ultraviolet to red light, respectively. Note that the matching of photocatalyst and light was critical for success. Therefore, this review mainly focuses on the discussion of Ni‐metallaphotoredox BHA according to the irradiation light's wavelength, covering ultraviolet, purple, blue, red, and white light as well as solar light. We try to find a clue in the relationship of structure‐photophysical behaviors of photocatalysts under the same or different irradiation light. At last, current limitations and potential trends for advancing Ni‐metallaphotoredox BHA are highlighted. We deem that it could encourage chemists to continue designing suitable photocatalyst for C−N bond formations under sunlight mimicking plants’ photosynthesis.

Unravelling the Role of the Pentafluoroorthotellurate Group as a Ligand in Nickel Chemistry.

The pentafluoroorthotellurate group (teflate, OTeF5 ) is able to form species, for which only the fluoride analogues are known. Despite nickel fluorides being widely investigated, nickel teflates have remained elusive for decades. By reaction of [NiCl4 ]2- and neat ClOTeF5 , we have synthesized the homoleptic [Ni(OTeF5 )4 ]2- anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF4 ]2- . This high-spin complex has allowed the study of the electronic properties of the teflate group, which can be classified as a weak/medium-field ligand, and therefore behaves as the fluoride analogue also in ligand-field terms. The teflate ligands in [NEt4 ]2 [Ni(OTeF5 )4 ] are easily substituted, as shown by the formation of [Ni(NCMe)6 ][OTeF5 ]2 by dissolving it in acetonitrile. Nevertheless, careful reactions with other conventional ligands have enabled the crystallization of nickel teflate complexes with different coordination geometries, i.e. [NEt4 ]2 [trans-Ni(OEt2 )2 (OTeF5 )4 ] or [NEt4 ][Ni(bpyMe2 )(OTeF5 )3 ].

(Digital Presentation) Time-Resolved Operando XAS of FexNi100-XOy Electrocatalysts for the Oxygen Evolution Reaction Reveals Temporal Shift in Ni K-Edge during Ni2+/3+ Redox Reaction

FexNi100-xOy electrocatalysts have become a focus for alkaline water electrolysis and the oxidative half reaction of oxygen evolution. Under alkaline conditions, the oxygen evolution reaction (OER) can be promoted by non-precious metal oxide and hydroxide electrocatalysts. In particular, electrocatalyst compositions from first row late transition metals such as iron, nickel, manganese, and cobalt have emerged as some of the most active catalysts for the OER, and the role of iron has been identified as key within multi-metallic compositions. In our research, we have focused specifically on the iron-nickel bimetallic composition and have developed synthesis methods to be able to control the bimetallic composition, surface chemistry, and three-dimensional morphology of a suite of FexNi100-xOy nanoparticle electrocatalysts. With this subset of highly-active FexNi100-xOy nanoparticle electrocatalysts, we have recently been focused on operando x-ray absorption spectroscopy (XAS) studies to understand how the chemistry of the iron and nickel species within these nanocatalysts changes as a result of exposure to the electrochemical environment. This talk will focus on a set of operando data obtained with a quick scan detector at beamline 9-3 at SSRL, where we were able to capture temporal, dynamic changes to the nickel chemistry as a function of applied voltage in the Faradaic region of the OER. Specifically, we have captured the change in the Ni K-edge that occurs as a result of the voltage stepping through the Ni redox reaction, where the Ni species in our electrocatalyst oxidizes from a 2+ to a 3+/4+ oxidation state. This redox reaction is associated with a phase transition from Ni(OH)2 to NiOOH. Our measurements were able to obtain 90 s scans during a 15 min time period of measurement, where we find that the Ni redox reaction and phase transition occurs during the first 10 minutes of measurement. Modeling of the extended x-ray absorption fine structure (EXAFS) region suggests that both Ni – O and Ni – M (M = metal) scattering path atomic pairs undergo a compression in distance. Further, the time scale of the phase transition suggests that the Ni redox reaction is mass transport limited. In this talk, I will discuss these results and present our analysis of the time-resolved x-ray absorption spectroscopy data.

Case Study of N-i Pr versus N-Mes Substituted NHC Ligands in Nickel Chemistry: The Coordination and Cyclotrimerization of Alkynes at [Ni(NHC)2

A case study on the effect of the employment of two different NHC ligands in complexes [Ni(NHC)2] (NHC= i Pr2ImMe 1Me , Mes2Im 2) and their behavior towards alkynes is reported. The reaction of a mixture of [Ni2( i Pr2ImMe)4(μ‐(η 2 : η2)‐COD)] B/ [Ni( i Pr2ImMe)2(η4‐COD)] B’ or [Ni(Mes2Im)2] 2, respectively, with alkynes afforded complexes [Ni(NHC)2(η2‐alkyne)] (NHC= i Pr2ImMe: alkyne=MeC≡CMe 3, H7C3C≡CC3H7 4, PhC≡CPh 5, MeOOCC≡CCOOMe 6, Me3SiC≡CSiMe3 7, PhC≡CMe 8, HC≡CC3H7 9, HC≡CPh 10, HC≡C(p‐Tol) 11, HC≡C(4‐ t Bu‐C6H4) 12, HC≡CCOOMe 13; NHC=Mes2Im: alkyne=MeC≡CMe 14, MeOOCC≡CCOOMe 15, PhC≡CMe 16, HC≡C(4‐ t Bu‐C6H4) 17, HC≡CCOOMe 18). Unusual rearrangement products 11 a and 12 a were identified for the complexes of the terminal alkynes HC≡C(p‐Tol) and HC≡C(4‐ t Bu‐C6H4), 11 and 12, which were formed by addition of a C−H bond of one of the NHC N‐ i Pr methyl groups to the C≡C triple bond of the coordinated alkyne. Complex 2 catalyzes the cyclotrimerization of 2‐butyne, 4‐octyne, diphenylacetylene, dimethyl acetylendicarboxylate, 1‐pentyne, phenylacetylene and methyl propiolate at ambient conditions, whereas 1Me is not a good catalyst. The reaction of 2 with 2‐butyne was monitored in some detail, which led to a mechanistic proposal for the cyclotrimerization at [Ni(NHC)2]. DFT calculations reveal that the differences between 1M e and 2 for alkyne cyclotrimerization lie in the energy profile of the initiation steps, which is very shallow for 2, and each step is associated with only a moderate energy change. The higher stability of 3 compared to 14 is attributed to a better electron transfer from the NHC to the metal to the alkyne ligand for the N‐alkyl substituted NHC, to enhanced Ni‐alkyne backbonding due to a smaller CNHC−Ni−CNHC bite angle, and to less steric repulsion of the smaller NHC i Pr2ImMe.

Synthetic Applications of Nickel-Catalyzed Cross-Coupling and Cyclisation Reactions.

Since the first studies about fifty years ago, the direct formation of C-C bonds, catalyzed by nickel complexes, has appeared as an important research topic, and has re-emerged recently as a renewal of nickel chemistry. This account provides a summary of the use of nickel complexes in catalysis, and highlights the evolution of our own research.

Synthetic investigations of low-coordinate (N-phosphino-amidinate) nickel chemistry: agostic alkyl complexes and benzene insertion into Ni-H.

Treatment of (PN)NiX (X = NHdipp or OtBu; PN = N-phosphinoamidinate ligand) with Me2PhSiH in benzene solvent afforded the crystallographically characterized, antifacial-coordinated, dinuclear species 1, the formation of which corresponds to the hitherto unknown net Ni-H addition of two equivalents of the putative (PN)NiH intermediate across C[double bond, length as m-dash]C units within a single benzene molecule. Computational analysis supports the view of 1 as being comprised of two cationic (PN)NiII fragments ligated by a substituted butadiene dianion μ2-η3:η3-C6H82- bridging group. Also described is the formation and characterization of three-coordinate (PN)Ni(alkyl) complexes stabilized by β-agostic (alkyl = Et, 2; n-Bu, 3; n-hexyl, 4) or γ-agostic (alkyl = neopentyl, 5) interactions, and our efforts to employ 2 and 3 as synthons for the generation of (PN)NiHvia β-hydride elimination. Notably, compound 5 represents both the first crystallographically characterized three-coordinate Ni-alkyl complex featuring a heterobidentate ligation, and the first neutral γ-agostic NiII-alkyl complex.

Template effect using aroylhydrazone ligand: Synthesis, crystal structure and magnetic properties of a novel ferromagnetically coupled heptanuclear nickel(II) cluster with a vertex-shared dicubane structure

The reaction of aroylhydrazone ligand H2L with Ni(II) metal ions afforded, upon crystallization under aerobic conditions, a novel heptanuclear Ni(II) cluster without this ligand (template effect of aroylhydrazone ligand). The heptanuclear [NiII7] compound 1 displays a metallic core which can be presented as a vertex-shared dicubane structure. Noteworthy, (i) this ligand is used for the first time in coordination chemistry, and (ii) this cluster does represent the first example in Nickel chemistry that possesses this topology with a structure not supported by any organic bridging ligand.

A Ni11 Coordination Cluster from the Use of the Di-2-Pyridyl Ketone/Acetate Ligand Combination: Synthetic, Structural and Magnetic Studies

The combined use of di-2-pyridyl ketone, (py)2CO, and acetates (MeCO2−) in nickel(II) chemistry in H2O-MeCN under basic conditions (Et3N) afforded the coordination cluster [Ni11(OH)6(O2CMe)12{(py)2C(OH)(O)}4(H2O)2] (1) in 80% yield, where (py)2C(OH)(O)− is the monoanion of the gem-diol form of (py)2CO. The complex contains a novel core topology. The core of 1 comprises a central non-linear {Ni3(μ2-OH)4}2+ subunit which is connected to two cubane {Ni4(OH)(μ3-OR)2(μ3-OR′)}4+ subunits [RO− = (py)2C(OH)(O)− and R′O− = MeCO2−] via the OH− groups of the former which become μ3. The linkage of the Ni3 subunit to each Ni4 subunit is completed by two η1:η1:μ2 and one η1:η3:μ4 MeCO2− groups. Peripheral ligation is provided by two terminal monodentate MeCO2− and two terminal aqua ligands. The (py)2C(OH)(O)− ligands adopt the η1:η1:η3:μ3 coordination mode. From the twelve MeCO2− ligands, two are η1, two η1:η3:μ4 and eight adopt the syn, syn η1:η1:μ2 coordination mode; four of the latter bridge NiII centers at opposite faces of the cubane subunits. Complex 1 is the largest nickel(II)/(py)2CO-based ligand coordination cluster discovered to date and has an extremely rare nuclearity (Ni11) in the cluster chemistry of nickel(II). Variable-temperature, solid state dc susceptibility, and variable-field magnetization studies at low temperatures were carried out on complex 1. The study of the data reveals an S = 3 ground state, which has been well rationalized in terms of known magnetostructural correlations and the structural features of 1. An attempt has also been made to interpret the magnetic properties of the undecanuclear cluster in a quantitative manner using four exchange interaction parameters and the obtained J values are discussed. The role of H2O in the solvent medium that led to 1, and the high nickel(II) and acetate to di-2-pyridyl ketone reaction ratio employed for its preparation, on the nuclearity and identity of the cluster are critically analyzed.

Light unlocks a new pathway for nickel chemistry

Light unlocks a new pathway for nickel chemistry

Organonickel(IV) chemistry: a new catalyst?

With scorpionate ligands finding their way into organonickel chemistry, the state of the art of present-day nickel(IV) chemistry is highlighted. Will rapid CX coupling reactions emerge as a domain of higher-oxidation-state nickel chemistry?

A new PC(sp(3))P ligand and its coordination chemistry with low-valent iron, cobalt and nickel complexes.

A new PC(sp(3))P ligand N,N'-bis(diphenylphosphino)dipyrromethane [PCH2P] (1) was prepared and its iron, cobalt and nickel chemistry was explored. Two pincer-type complexes [PCHP]Fe(H)(PMe3)2 (2) and [PCHP]Co(PMe3)2 (4) were synthesized in the reaction of with Fe(PMe3)4 and Co(Me)(PMe3)4. 1 reacted with Co(PMe3)4 and Ni(PMe3)4 to afford Co(0) and Ni(0) complexes [PCH2P]Co(PMe3)2 (3) and [PCH2P]Ni(PMe3)2 (5). The structures of complexes 2-5 were determined by X-ray diffraction.

Use of 6-methylpyridine-2-carbaldehydeoxime in nickel(ii) carboxylate chemistry: synthetic, structural and magnetic properties of penta and hexanuclear complexes

The use of 6-methylpyridine-2-carbaldehydeoxime ligand (6-mepaoH), in nickel(II) chemistry has been investigated and three new clusters isolated in mild conditions. Depending on the nature of the metal starting salts and the reaction conditions, the Ni(II)/6-mepaoH system has provided access to the complexes [Ni(6)(O(2)CPh)(6)(6-mepao)(6)] (1), [Ni(6)(O(2)CMe)(6)(6-mepao)(6)] (2) and [Ni(5)(3-Cl-BzO)(4)(6-mepao)(4)(6-mepaoH)(2)(N(3))(2)] (3), where 3-Cl-BzO(-) is the 3-chlorobenzoate anion. Compounds 1 and 2 are two new members of the [Ni(6)(O(2)C-R)(oximato)(6)] family of hexanuclear complexes whereas 3 exhibits an unusual irregular bowtie topology including end-on azido bridges. The structures of the three compounds have been determined by single-crystal X-ray crystallography. Variable-temperature dc magnetic susceptibility studies were carried out for 1-3. The data indicate antiferromagnetic exchange for complexes 1 and 2 and ferrimagnetic interaction for complex 3.

A structure and reactivity analysis of monomeric Ni(II)-hydroxo complexes prepared from water.

The nickel(ii) chemistry with the tridentate ligands bis[(N'-R-ureido)-N-ethyl]-N-methylamine (H(4)(R), R = isopropyl, tert-butyl) is described. The Ni(ii)-OH complexes, [Ni(II)H(2)(R)(OH)](-) were generated using water as the source of the hydroxo ligand. These complexes are pseudo-square planar, in which the primary coordination sphere contains three nitrogen donors from [H(2)(R)](2-) and the oxygen atom from the hydroxide (Ni-O(H), 1.857(1) A). The Ni(ii)-OH unit also is involved in two intramolecular hydrogen bonds between the urea groups of the [H(2)(R)](2-) and the hydroxo oxygen atom. Attempts to deprotonate the Ni(ii)-OH unit to produce Ni(ii)-oxo complexes were unsuccessful. A variety of bases with pK(a) of less than 15 (in DMSO) were unable to deprotonate the hydroxo ligand. Treating the Ni(ii)-OH complexes with KOBu(t) (pK(a) approximately 29) afforded the ligand substitution product, [Ni(II)H(2)(R)(OBu(t))](-). Ni(ii)-siloxide complexes were isolated when the [Ni(II)H(2)(R)(OH)](-) complexes were allowed to react with K[N(TMS)(2)].

Studies on Nickel(II) Complexes with Amide‐Based Ligands: Syntheses, Structures, Electrochemistry and Oxidation Chemistry

AbstractThe present work discusses the nickel chemistry in a set of amide‐based open‐chain ligands with subtle differences in the backbone or terminal amine substituents. The ligands coordinate to the Ni2+ ion through the Namide and Namine atoms maintaining a square‐planar geometry. Absorption spectra and NMR studies reveal that the solid‐state square‐planar geometry is retained in solution. The electrochemical results suggest that the NiIII/NiII redox couple primarily depends on the N4 donors, which is composed of two Namide and twoNamine atoms and not on the peripheral substituents. All four ligands with variable backbone and substituents are equally competent in stabilizing the NiIII state. On the basis of electrochemical findings, chemical oxidations were carried out, and they reveal generation of the NiIII state in two cases, whereas decomposition was observed in others. Preliminary alkene epoxidation reactions suggest that the present nickel complexes transiently stabilize the higher oxidation state of the nickel ion that possibly participates in the oxidation of the substrates.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Use of the Sulfato Ligand in 3d‐Metal Cluster Chemistry: A Family of Hexanuclear Nickel(II) Complexes with 2‐Pyridyl‐Substituted Oxime Ligands

AbstractThe initial use of 2‐pyridyl‐substituted oximes [(py)C(R)NOH; R = Me, Ph]/sulfate blend in nickel(II) chemistry has yielded a family of hexanuclear clusters. The syntheses, structures and magnetic properties are reported of [Ni6(SO4)4(OH){(py)C(Me)NO}3{(py)C(Me)NOH}3(MeOH)2(H2O)] (1),[Ni6(SO4)4(OH){(py)C(ph)NO}3{(py)C(ph)NOH}3(MeOH)3] (2)and [Ni6(SO4)4(OH){(py)C(ph)NO}3{(py)C(ph)NOH}3(H2O)3] (3), where (py)C(Me)NOH is methyl 2‐pyridyl ketone oxime and (py)C(ph)NOH is phenyl 2‐pyridyl ketone oxime. The hexanuclear molecules present in the three complexes have similar structures which contain the [Ni6(μ3‐OH)(μ3‐SO4)3(μ3‐ONR)3]2+ core. The core consists of six NiII ions arranged as two parallel equilateral triangular subunits, one small (Ni···Ni ca. 3.3 Å) and the other larger (Ni···Ni ca. 6.0 Å). Characteristic IR bands are discussed in terms of the known structures of 1–3. The magnetic properties of 1 and 2 have been studied by variable‐temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions. A simple 2‐J model was found to be adequate to describe the similar thermal variation of the molar magnetic susceptibilities of 1 and 2.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

2-Pyridyloximate clusters of cobalt and nickel

The use of 2-pyridyloximate(-1) ligands, (py)C(R)NO − [R = H, Ph, 2-pyridyl (py)] in cobalt and nickel(II) chemistry has been investigated and led to four families of clusters. A representative member of each family, namely [ Co II Co 2 III { ( py ) C ( ph ) NO } 6 ] ( PF 6 ) 2 ( 1), [ Co 2 II Co 2 III ( OH ) 2 ( O 2 CMe ) 2 { ( py ) 2 CNO } 4 ( MeOH ) 2 ] ( ClO 4 ) 2 ( 2), [Ni 9(OH) 4{(py)CHNO} 10(H 2O) 8]{N(CN) 2} 3(ClO 4) [ 3{N(CN) 2} 3(ClO 4)] and [Ni 4(O 2CMe) 4{(py)C(ph)NO} 4(MeOH) 2] ( 4) is briefly structurally and magnetically described.

Enneanuclear Ni(II) complexes from the use of the flexible ligand 2-pyridinealdoxime: The nature of the inorganic anion does not affect the chemical and structural identity of the cationic cluster

The use of 2-pyridinealdoximate(−1) [(py)CHNO −] in nickel(II) chemistry has been further investigated. The synthetic investigation has led to two new salts of the very recently reported (in the form of its tetraperchlorate salt, 1) enneanuclear cation [Ni 9(μ 3-OH) 2(μ 2-OH) 2{μ 3-(py)CHNO} 4{μ 2-(py)CHNO} 6(μ 2-OH 2) 2(H 2O) 6] 4+. The two new cationic clusters [Ni 9(OH) 4{(py)CHNO} 10(H 2O) 8](SCN) 2(OH) 2 · 9.91H 2O ( 2 · 9.91H 2O) and [Ni 9(OH) 4{(py)CHNO} 10(H 2O) 8]{N(CN) 2} 3(ClO 4) · 11.11H 2O ( 3 · 11.11H 2O) have been structurally characterized by single-crystal X-ray crystallography at 100 K. The nature of the inorganic anions (Cl −/SCN −, N ( CN) 2 - / ClO 4 - ) present in the reaction mixtures does not affect the chemical and structural identity of the enneanuclear cation. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the complexes. The variable-temperature magnetic susceptibility data of 1, which had also been obtained by our group, were simulated by means of a 3- J model, which is compared with the 2- J model reported for this cluster by Chaudhuri and co-workers [S. Khanra, T. Weyhermüller, E. Rentschler, P. Chaudhuri, Inorg. Chem. 44 (2005) 8176]. The ground-state total spin of the cluster is S T = 1.

Heptanuclearity in nickel(II) chemistry: preparation, characterization, crystal structure and magnetic properties of [Ni 7(OH) 2(acac) 8(btaO) 4(H 2O) 2] (btaO −=the 1-hydroxybenzotriazolate ion)

The use of the substituted benzotriazole ligand btaOH (1-hydroxybenzotriazole) in nickel(II) chemistry has yielded a structurally and magnetically interesting polynuclear complex. The [Ni(acac) 2(H 2O) 2]–btaOH·H 2O (4:1, 3:1, 7:4) reaction system in refluxing MeCN gives light green–blue [Ni 7(OH) 2(acac) 8(btaO) 4(H 2O) 2] ( 4) in good yield (∼75%). The structure of 4·MeCN·0.9H 2O was determined by single-crystal X-ray crystallography. The heptanuclear assembly is held together by two μ 3 hydroxo ligands, two terminal H 2O molecules, four chelating acac − groups, two μ 2 acac − groups, two μ 3 acac − groups, two μ 4 btaO − ligands and two μ 2 btaO − ligands. The Ni(II) atoms have distorted octahedral geometries. The IR and UV–Vis data of 4 are discussed in terms of the nature of bonding and the known structure. Variable-temperature magnetic susceptibility data (3–300 K), fitted with a 3- J model, show ferromagnetic and antiferromagnetic interactions. Magnetization data at 4 K are in line with an S=1 ground state for 4. The versatility of the 1-hydroxybenzotriazolate ligand is also discussed.

The first 3-D ferrimagnetic nickel fumarate with an open framework: [Ni3(OH)2(O2C-C2H2-CO2)(H2O)4].2H2O.

A three-dimensional nickel fumarate has been isolated by hydrothermal reaction and its structure solved from powder X-ray diffraction; its organisation reveals an unusual topology not previously seen in nickel chemistry and provided a scarce ferrimagnetic behaviour below 20 K.