Homoleptic Nickel Research Articles

Homoleptic nickel(II)-dithiocarbamates as potent homogeneous electrocatalysts for hydrogen evolution reaction: Effect of positional isomeric –OH group on electrocatalytic properties

Three positional isomeric homoleptic Ni(II) dithiocarbamate complexes having general formula [Ni(L)2] (L=N-benzyl-1-(2-hydroxyphenyl) dithiocarbamate (Ni-1); N-benzyl-1-(3-hydroxyphenyl) dithiocarbamate (Ni-2) and N-benzyl-1-(4-hydroxyphenyl) dithiocarbamate (Ni-3)) have been synthesized and characterized by elemental analysis, FT-IR, UV–Vis., multinuclear NMR spectroscopy and single crystal X-ray diffraction. The single crystal X-ray analysis for Ni-2 reveals distorted square planar geometry around Ni(II), that is satisfied by four sulfur centers of two N-benzyl-1-(3-hydroxyphenyl) dithiocarbamate ligands. The nature of weak interactions in Ni-2 have been explored using Hirshfeld surface analysis, which suggest that the percentage contribution of O···H interactions is more than S···H interactions. These complexes have been employed as homogeneous catalysts for electrochemical hydrogen evolution reaction suggesting turnover frequency (TOF) of 566.2, 457.2 and 867.9 s−1 for Ni-1, Ni-2 and Ni-3, respectively on adding 30 mM trifluoroacetic acid (TFA). Also, the overpotential (η) values for Ni-1, Ni-2 and Ni-3 are 0.862, 0.872 and 0.723 V, respectively. The variation in the electrocatalytic properties was explained on the basis of theoretical calculations which suggested that the para-OH isomer complex possess relatively larger HOMO-LUMO energy gap, compared to ortho-OH and meta-OH isomeric complexes and indicated the relative less stable nature of para-OH isomer complex and its better susceptibility towards electrons at a lower negative potential.

Isolation and Characterization of the Homoleptic Nickel(I) and Nickel(II) Bis-benzene Sandwich Cations.

A stable salt of the metalloradical [Ni(C6 H6 )2 ]+ hitherto unknown in the condensed phase was synthesized from [Ni(CO)4 ]+ [WCA]- and benzene ([WCA]- =[F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ). Single crystal XRD reveals a remarkable asymmetrically η3 ,η6 -slipped sandwich structure. The magnetic properties of the [Ni(C6 H6 )2 ]+ cation were determined in solution and in the gas phase. Oxidation with the synergistic Ag+ /0.5 l2 system led to the salt [Ni(C6 H6 )2 ]2+ ([WCA]- )2 . All products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.

Transformation of brucine into trifluoromethyl neobrucine using the homoleptic nickel catalyst [Ni(CF3)4]2−

The homoleptic trifluoromethyl nickel complex [Ni(CF3)4]2− catalyzes a stereoselective trifluoromethylation of brucine with Umemoto II reagent. The trifluoromethylation process proceeds with concomitant isomerization of its alkenyl double bond leading to a trifluoromethylated neobrucine-like derivative. A minor difunctionalization product was also detected from the reaction mixture, consistent with a radical addition process that is occurring in parallel. Stoichiometric reactions between the nickel(II) catalyst precursor and brucine led to no reaction. However, a stochiometric reaction with a high-valent nickel(IV) complex formed trifluoromethylated neobrucine, implicating its intermediacy.

Frontispiece: Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl‐Nitrosyl Analogue

Coordination Complexes In their Communication on page 14800, Ingo Krossing et al. report the synthesis of the first homoleptic nickel carbonyl cation [Ni(CO)4]·+ and the nickel tricarbonyl-nitrosyl cation [Ni(CO)3(NO)]+ in the condensed phase.

Frontispiz: Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl‐Nitrosyl Analogue

Koordinationsverbindungen In ihrer Zuschrift auf S. 14926 berichten Ingo Krossing et al. über die Synthese des ersten homoleptischen Nickelcarbonyl-Kations [Ni(CO)4]·+ und des Nickel-Tricarbonyl-Nitrosyl-Kations [Ni(CO)3(NO)]+ in der kondensierten Phase.

Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl-Nitrosyl Analogue.

130 years after Mond discovered the first homoleptic carbonyl complex Ni(CO)4, we report on a [Ni(CO)4].+ salt as the first synthesis of any homoleptic nickel carbonyl cation in the condensed phase. It was prepared by oxidation of nickel metal with the synergistic oxidant Ag[F{Al(ORF)3}2]/0.5 I2 (RF=C(CF3)3) in CO atmosphere. This D2d‐symmetric metalloradical represents the last missing entry among the structurally characterized homoleptic carbonyl cations of Groups 6 to 11. Additionally, the nickel tricarbonyl‐nitrosyl cation [Ni(CO)3(NO)]+ was obtained by usage of NO[F{Al(ORF)3}2] and all products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.

Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl‐Nitrosyl Analogue

Abstract130 years after Mond discovered the first homoleptic carbonyl complex Ni(CO)4, we report on a [Ni(CO)4].+ salt as the first synthesis of any homoleptic nickel carbonyl cation in the condensed phase. It was prepared by oxidation of nickel metal with the synergistic oxidant Ag[F{Al(ORF)3}2]/0.5 I2 (RF=C(CF3)3) in CO atmosphere. This D2d‐symmetric metalloradical represents the last missing entry among the structurally characterized homoleptic carbonyl cations of Groups 6 to 11. Additionally, the nickel tricarbonyl‐nitrosyl cation [Ni(CO)3(NO)]+ was obtained by usage of NO[F{Al(ORF)3}2] and all products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.

Unsaturated binuclear homoleptic nickel carbonyl anions Ni2(CO)n- (n = 4-6) featuring double three-center two-electron Ni-C-Ni bonds.

The homoleptic homodinuclear nickel carbonyl anions Ni2(CO)n- (n = 4-6) are mass-selected in the gas phase and examined with anion photoelectron velocity-map imaging spectroscopy combined with density functional calculations. The doubly carbonyl-bridged structures are found to be favorable for Ni2(CO)n- (n = 4-6). The nature of Ni-Ni bonding in these complexes is analysed with the aid of a range of state-of-the-art quantum chemistry methods. Despite the absence of direct multiple Ni-Ni bonds, the two nickel atoms in Ni2(CO)n- (n = 4-6) complexes are joined by two bridging carbonyl ligands via the sharing three-center two-electron Ni-C-Ni bond in turn to achieve the (16,16), (16,18), and eventually the favored (18,18) configurations.

Theoretical, antimicrobial, antioxidant, in vitro cytotoxicity, and cyclin-dependent kinase 2 inhibitor studies of metal(II) complexes with bis(imidazol-1-yl)methane-based heteroscorpionate ligands

A series of C-centered heteroscorpionate-based homoleptic manganese(II), nickel(II), and copper(II) complexes of type [M(L1–3)2] (1–9) have been synthesized by using the ligands (2-hydroxyphenyl)bis(imidazol-1-yl)methane (HL1), (4-diethylamino-2-hydroxyphenyl)bis(imidazol-1-yl)methane (HL2) and (5-bromo-2-hydroxyphenyl)bis(imidazol-1-yl)methane (HL3). The geometric parameters of the complexes were determined using UV-vis and theoretical studies suggesting distorted octahedral geometry around metal(II) ion. Frontier molecular orbital analysis supports bioefficacy of the complexes. Antimicrobial activity of the metal(II) complexes were determined against two Gram(–ve) (Escherichia coli and Klebsiella pneumoniae) and two Gram(+ve) (Bacillus cereus and Staphylococcus aureus) bacteria, and three fungal (Candida albicans, Candida glabrata, and Candida krusei) strains. Antioxidant activity of nickel(II) and copper(II) complexes were evaluated against ABTS, DPPH, and H2O2 free radicals. In vitro cytotoxicity activity of nickel(II) and copper(II) complexes against human breast adenocarcinoma (MCF-7), cervical (HeLa), and lung (A549) cancer cell lines along with one normal human dermal fibroblasts (NHDF) cell line were carried out by MTT assay, which shows the potent activity of copper(II) complex 8 with respect to the standard drug cisplatin. Molecular docking studies evidence the interaction of complexes with cyclin-dependent kinase 2 receptor (CDK2).

Highly active homoleptic nickel(II) bis-N-heterocyclic carbene catalyst for Suzuki–Miyaura and Heck cross-coupling reactions

New homoleptic nickel(II) biscarbene complex was synthesized and structurally characterized. The complex depicted the excellent catalytic activities with only 3 mol% catalyst loading along with wide substrate scope for the Suzuki–Miyaura cross-coupling reactions (twenty six examples) and Heck coupling reactions (eighteen examples).

Synthesis and characterization of homoleptic group 10 dithiocarbamate complexes and heteroleptic Ni(II) complexes, and the use of the homoleptic Ni(II) for the preparation of nickel sulphide nanoparticles

A series of new dithiocarbamate complexes of Ni(II), Pd(II) and Pt(II) of the form [NiL2], [PdL2] and [PtL2] (where L = N-ethyl-N-ethanoldithiocarbamate) have been synthesized and characterized by elemental analysis, FTIR, and 1H and 13C NMR spectroscopy. The nickel complex was utilized to prepare heteroleptic complexes bearing triphenylphosphino (PPh3) and isothiocyanate (NCS) or isocyanide (NC) molecules. Furthermore, the structures of the palladium complex and the heteroleptic nickel with PPh3 and NC molecules have been confirmed by X-ray diffraction. The Pd(II) complex indicated a trans arrangement with a distorted square planar geometry around the Pd atom, while the Ni(II) complex revealed a highly distorted geometry with another molecule of triphenylphosphine moiety, held by hydrogen bonding, within the crystal structure. The thermal stability studies of all the complexes conducted by using thermogravimetric analyser (TGA) showed they all have good stability above 200 °C. The nanoparticles synthesized using the homoleptic nickel complex yielded platelets of pure Heazlewoodite phase of Ni3S2 with average size of 7.60 nm. The optical properties of the nanoparticles studied by using UV–vis spectroscopy showed band gap energy of 4.0 eV (355 nm), which was a blue shift of 1.90 eV compared to the bulk and a consequence of quantum confinement effect.

In situ oxidation triggered heteroleptically deprotonated cobalt(III) and homoleptic nickel(II) complexes of diacetyl monoxime derived tri-nitrogen chelators; Synthesis, molecular structures and biological assay

Two tri-nitrogen chelating unsymmetrical Schiff base ligands, 3-(hydroxyimino)-2-butanone-2-(1H-benzothiazol-2-yl)hydrazone and 3-(hydroxyimino)-2-butanone-2-(1H-benzimidazol-2-yl)hydrazone are synthesized by the condensation reaction of diacetyl monoxime with 2-hydrazino-benzothiazole/benzimidazole. Ligands have shown ML2 type octahedral coordination towards Ni(II) and in situ generated Co(III) ions. Ligands and complexes are characterized by various spectro-analytical techniques. Both the ligands have shown a similar mode of ligation, but a different mode of deprotonation towards the cobalt and nickel ions. Ligands are left neutral in the case of nickel complexes while anionic in the case of cobalt complexes. Further, in situ oxidation of Co(II) to Co(III) has triggered a different mode of deprotonation between the two ligands of the same cobalt complex. Out of the four complexes synthesized, three complexes are characterized by single crystal X-ray diffraction technique, to evidence the structural facts. A comparative account of bond lengths of two complexes of the benzothiazole based ligand is presented. Structures of all the four complexes have been checked preliminarily for their NCI-60 Human Cancer Cell Line anticancer screening. Further, one among the four, the nickel complex of benzothiazole core is used for one dose growth inhibition screening against 60 different human cancer cell lines. The tested complex has shown highest growth inhibition over a Non-Small Cell Lung Cancer cell line EKVX. In addition, compounds are screened for their antibacterial and antifungal potencies against few microorganisms. The complexes have shown promising antimicrobial potencies.

Proton reduction reaction catalyzed by homoleptic nickel bis-1,2-dithiolate complexes: Experimental and theoretical mechanistic investigations.

A series of homoleptic monoanionic nickel dithiolene complexes [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4) containing the ligands benzene-1,2-dithiolate (bdt2-), toluene-3,4-dithiolate (tdt2-) and maleonitriledithiolate (mnt2-), respectively, have been employed as electrocatalysts in the hydrogen evolution reaction with trifluoroacetic acid as proton source in acetonitrile. All complexes were active catalysts with TONs reaching 113, 158 and 6 for [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4), respectively. Faradaic yield for hydrogen evolution reaction reaches 88 % for 2- , which also displays the minimal overpotential requirement value (467 mV) within the series. Two pathways for H2 evolution can be hypothesized that differ on on the sequence of protonation and reduction steps. DFT calculations are in agreement with experimental data and indicate that protonation at sulfur follows reduction to the dianion. Hydrogen evolves from the direduced-diprotonated form via a highly distorted nickel hydride intermediate. The effects of acid strength and concentration in the hydrogen-evolving mechanism are also discussed.

Cyclization of thiocarbonyl groups in binuclear homoleptic nickel thiocarbonyls to give ligands derived from sulfur analogues of croconic and rhodizonic acids.

The sulfur analogue of the well-known Ni(CO)4, namely, Ni(CS)4, has been observed spectroscopically in low temperature matrices but is not known as a stable species under ambient conditions. Theoretical studies show that Ni(CS)4 with monomeric CS ligands and tetrahedrally coordinated nickel is disfavored by ∼17 kcal/mol relative to unusual isomeric Ni(C2S2)2 structures. In the latter structures the CS ligands couple pairwise through C-C bond formation to give dimeric S═C═C═S ligands, which bond preferentially to the nickel atom through their C═S bonds rather than their C═C bonds. Coupling of CS ligands in the lowest energy binuclear Ni2(CS)n (n = 7, 6, 5) structures results in cyclization to give remarkable CnSn (n = 5, 6) ligands containing five- and six-membered carbocyclic rings. Such ligands, which are the sulfur analogues of the well-known croconate (n = 5) and rhodizonate (n = 6) oxocarbon ligands, function as bidentate ligands to the central Ni2 unit. Higher energy Ni2(CS)n (n = 7, 6, 5) structures contain dimeric C2S2 ligands, which can bridge the central Ni2 unit. Dimeric C2S2 ligands rather than tetrathiosquare C4S4 ligands are found in the lowest energy Ni2(CS)4 structures.

Synthesis, spectral and antibacterial studies on Ni(II) and Zn(II) complexes involving N-furfuryl-N-isopropyldithiocarbamate (f iprdtc) and Lewis bases: X-ray structure of [Ni(f iprdtc)(NCS)(PPh3)

[Ni(fiprdtc)2] (1), [Ni(fiprdtc)(PPh3)(NCS)] (2), [Ni(fiprdtc)(PPh3)2]ClO4 (3), [Zn(fiprdtc)2] (4), [Zn(fiprdtc)2(1,10-phen)] (5) and [Zn(fiprdtc)2(2,2′-bipy)] (6) (f iprdtc=N-furfuryl-N-isopropyldithio- carbamate, 1,10-phen=1,10-phenanthroline and 2,2′-bipy=2,2′-bipyridine) complexes were prepared and characterized by elemental analysis, electronic, IR and NMR spectra and the structure of 2 was determined by single-crystal X-ray crystallography. UV–Vis spectral data of 1–3 are consistent with the formation of square planar complexes. IR spectra of the complexes show the contribution of the thioureide form to the structure. A single-crystal X-ray structural analysis of 2 proved four-coordinated nickel in a distorted square planar arrangement with a S2PN donor set. Significant asymmetry in Ni–S bond distances was observed in [Ni‒ S1=2.1655(8); Ni‒ S2=2.2120(8) Å]. This observation clearly supports the less effective trans of SCN− over PPh3. The observed shielding in N13CS2 chemical shifts of heteroleptic nickel complexes 2 and 3 when compared with homoleptic nickel complex 1 indicates the effect of PPh3 on the mesomeric drift of electron density toward nickel through the thioureide C‒ N bond. The N13CS2 chemical shift of 5 and 6 are additionally deshielded compared with 4 owing to the increase in coordination number. Complexes were screened for in vitro antibacterial activity and significant activity has been found.

Infrared photodissociation spectra of mass selected homoleptic nickel carbonyl cluster cations in the gas phase

Infrared spectra of mass-selected homoleptic nickel carbonyl cluster cations including dinuclear Ni2(CO)7(+) and Ni2(CO)8(+), trinuclear Ni3(CO)9(+) and tetranuclear Ni4(CO)11(+) are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. The Ni2(CO)7(+) cation is characterized to have an unbridged asymmetric (OC)4Ni-Ni(CO)3(+) structure with a Ni-Ni single bond. The Ni2(CO)8(+) cation has a Ni-Ni half-bonded D3d structure with both nickel centers exhibiting an 18-electron configuration. The trinuclear Ni3(CO)9(+) cluster cation is determined to have an open chain like (OC)4Ni-NiCO-Ni(CO)4 structure. The tetranuclear Ni4(CO)11(+) cluster cation is determined to have a tetrahedral structure with two-center and three-center bridge-bonded carbonyl units. These nickel carbonyl cluster cations all involve trigonal pyramid like Ni(CO)4 building blocks that satisfy the 18-electron configuration of the nickel centers.

Iron(II) and Nickel(II) Complexes of N‐Alkylimidazoles and 1‐Methyl‐1H‐1, 2, 4‐Triazole: X‐ray Studies, Magnetic Characterization, and DFT Calculations

AbstractUsing the ligands N‐methylimidazole (MeIm), N‐ethylimidazole (EtIm), N‐propylimidazole (PrIm), and 1‐methyl‐1H‐1, 2, 4‐triazole (MeTz) three series with a total of 13 iron(II) complexes were isolated. The series comprise of the following complexes: (a) [Fe(MeIm)6](ClO4)2 (1), [Fe(EtIm)6](ClO4)2 (2), [Fe(PrIm)6](ClO4)2(3), [Fe(MeTz)6](ClO4)2 (4), [Fe(MeIm)6](MeSO3)2 (5), [Fe(EtIm)6](MeSO3)2 (6), and [Fe(MeTz)6](BF4)2 (10); (b) [Fe(MeIm)4(MeSO3)2](7), [Fe(EtIm)4(MeSO3)2] (8), and [Fe(PrIm)4(MeSO3)2] (9); (c) [Fe(MeIm)4(NCS)2] (15), [Fe(EtIm)4(NCS)2] (16), and [Fe(MeTz)4(NCS)2] (17). Single crystal X‐ray diffraction studies were performed on 7–10 and 15–17. Temperature dependent magnetic susceptibility measurements were performed on selective examples of all series, and confirmed them to be in the HS state over the range 6–300 K. DFT calculations were performed at BP86/def‐SV(P) and TPSSh/def2‐TZVPP level on all [FeL6]2+ complex cations and the neutral complexes 7–9 and 15–17. Additionally the four homoleptic nickel(II) complexes [NiL6](ClO4)2 (11: L = MeIm; 12: L = EtIm; 13: L = PrIm; 14: L = MeTz) were synthesized and compounds 11–13 structurally characterized. UV/Vis/NIR spectroscopic measurements were carried out on all homoleptic iron(II) and nickel(II) complexes. The 10Dq values were determined to be in the range of 11547–11574 and 10471–10834 cm–1 for the iron(II) and nickel(II) complexes, respectively.

A novel α-Po interpenetrating network with pseudo-double-wall pcu lattices based on the homoleptic nickel(II) node

Abstract A novel coordination polymer, {[Ni( bib ) 3 ](ClO 4 ) 2 } ∞ ( 1 ), was synthesized by the reaction of Ni(ClO 4 ) 2 ·6H 2 O with a linear rigid ligand 1,4-bis(imidazol-1-yl)benzene ( bib ). In this complex, the homoleptic octahedral nickel(II) node is connected by the rod-like spacer bib into an α-Po framework with larger pcu lattices, which are seemingly surrounded by double walls. The void space provided by the square-shaped channel is filled with another equivalent framework, i.e. complex 1 representing a unique interpenetrating α-Po topology network. Furthermore, magnetic study shows that there exists very weak antiferromagnetic exchange coupling in the complex.

Electrodeposition as a superior route to a thin film molecular semiconductor

Electrooxidation to form neutral films of a homoleptic nickel dithiolene [Ni(b-3ted)2] (1) from an air-stable TBA salt is described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene; TBA = tetrabutylammonium]. Films grown by potentiostatic electrodeposition directly onto interdigitated electrode arrays show improved conductivity compared to those formed by solution methods. The grown films are free from residual electrolyte doping, and this technique is shown to yield robust films of reproducible electronic performance. The conductivity of films formed by electrodeposition show gate dependence when grown directly onto field effect transistor substrates. Thin-film X-ray diffraction confirms the electrodeposited films to be of the same polymorph as films and single crystals formed by solution methods. Scanning electron microscopy shows the electrodeposited films to have larger, more connected polycrystalline regions, as well as improved contact with the electrodes.

Transmetalation of a Primary Amino-Functionalized N-Heterocyclic Carbene Ligand from an Axially Chiral Square-Planar Nickel(II) Complex to a Ruthenium(II) Precatalyst for the Transfer Hydrogenation of Ketones

The first homoleptic nickel(II) complex with primary amino-functionalized N-heterocyclic carbene (C−NH2) ligands ([Ni(m-CH2NH2)2](PF6)2, 2) was prepared under mild conditions by the reduction of a nitrile-functionalized imidazolium salt. This axially chiral, square-planar nickel(II) complex was characterized by NMR spectroscopy and an X-ray diffraction study. Enantiopure Δ-TRISPHAT was used as an NMR chiral shift reagent to observe the diastereotopic ion pairs by 1H NMR in acetonitrile-d3. A novel transmetalation reaction moved the primary amino-functionalized N-heterocyclic carbene ligand from the nickel(II) complex 2 to the [Ru(p-cymene)Cl]2 dimer, yielding the complex [Ru(p-cymene)(m-CH2NH2)Cl]PF6, (3), the first ruthenium(II) complex with such a chelating C−NH2 ligand. Complex 3 is a precatalyst for the transfer hydrogenation of acetophenone to 1-phenylethanol in basic 2-propanol at 75 °C with a turnover frequency of up to 880 h−1 and conversion of 96%.