Nickel Phosphine Complexes Research Articles

Comparative Analysis of Nickel-Phosphine Complexes with Cumulated Double Bond Ligands: Structural Insights and Electronic Interactions via ETS-NOCV and QTAIM Approaches.

This study presents a comprehensive analysis of nickel-phosphine complexes, specifically Ni(PH3)2(OCCH2), Ni(PH3)2(H2CCO), Ni(PH3)2(H2CCCH2), Ni(PH3)2(NNCH2), and Ni(PH3)2(η1-H2CNN). Utilizing ETS-NOCV analysis, we explored orbital energy decomposition and the Hirshfeld charges of the ligands, providing insights into the electronic structures and donor-acceptor interactions within these complexes. The interactions in the ketene and allene complexes exhibit similar deformation densities and NOCV orbital shapes to those calculated for Ni(PH3)2(NNCH2), indicating consistent interaction characteristics across these complexes. The total interaction energy for all η2 complexes is observed to be over 60 kcal/mol, slightly exceeding that of the analogous carbon dioxide complex reported earlier. Furthermore, the study highlights the stronger back-donation as compared to donor interactions across all η2 complexes. This is further corroborated by Hirshfeld analysis, revealing the charge distribution dynamics within the ligand fragments. The research offers new perspectives on the electron distribution and interaction energies in nickel-phosphine complexes, contributing to a deeper understanding of their catalytic and reactive behaviors.

Pure phase Ni12P5 anchored on N, P-codoped carbon nanosheet: A stable and highly efficient catalyst to reduce toxic organic compounds for continuous-flow application

The removal of toxic organic compounds from aqueous media through reduction reactions using nonnoble catalysts has attracted much attention in recent years. In this study, a simple method for the synthesis of pure-phase Ni12P5 nanoparticles supported on N, P-codoped carbon (NPC) sheets was developed, in which a nickel phosphine complex was selected as the precursor due to its high Ni/P ratio, air stability and easy preparation. By controlling the pyrolysis temperature, NixPy@NPC700 with a high dispersity and exposed active sites can be obtained, which was characterized by XRD, HRTEM, EDS, XPS, Raman and NH3-TPD. The catalytic performance of the composite in the reaction of 4-nitrophenol (4-NP) was assessed under mild conditions, exhibiting excellent catalytic activity with a low apparent activation energy Ea (29.87 KJ·mol−1). In addition, the catalyst can be recycled without obvious loss of activity for up to ten successive cycles. The outstanding hydrogenation activity is ascribed to the exposed Ni12P5(312) crystal plane of NixPy@NPC700, which is attributed to the lower energy barrier required to form a hydrogen splitting state according to DFT calculations. Moreover, NixPy@NPC700 was creatively coated in a Teflon tube with Nafion as the adhesive and constructed as a fixed-bed device. The continuous-flow catalytic reaction shows that the catalyst can maintain a satisfactory efficiency for approximately 6 h in the reduction of 4-NP and methyl orange (MO). These findings suggest that NixPy@NPC700 is an ideal catalyst for industrial applications for the chemical reduction of toxic compounds from wastewater.

Half-Sandwich Nickelacarboranes Derived from [7-(MeO(CH2)2S)-7,8-C2B9H11

New carboranyl thioethers 1-MeO(CH2)nS-1,2-C2B10H11 (n = 2, 3) were prepared by the alkylation of the trimethylammonium salt of 1-mercapto-ortho-carborane with 1-bromo- 2-methoxyethane and 1-bromo-3-methoxypropane, respectively. Their deboronation with cesium fluoride in ethanol gave the corresponding nido-carboranes Cs[7-MeO(CH2)nS-7,8-C2B9H11] (n = 2, 3). The reactions of Cs[7-MeO(CH2)2S-7,8-C2B9H11] with various nickel(II) phosphine complexes [(dppe)NiCl2] and [(R’R2P)2NiCl2] (R = R’ = Ph, Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) were studied and a series of nickelacarboranes 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 and 3,3- (R’R2P)2-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 (R = R’ = Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) was prepared. The molecular crystal structure of 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 was determined by single-crystal X-ray diffraction.

Interligand Interactions in Half-Sandwich Nickelacarboranes with Phosphine Ligands: Away from Skeletal Rearrangements

Reactions of nickel(II) phosphine complexes [(dppe)NiCl2], [(MePh2P)2NiCl2] and [(Ph3P)2NiCl2] with C-substituted nido-carboranes [7-R-nido-7,8-C2B9H11]− (R = Me, Ph, C(NHCy)2+) were studied. The reactions with [(dppe)NiCl2] lead to the corresponding nickelacarboranes 3,3-(dppe)-1-R-closo-3,1,2-NiC2B9H10 with absent or negligible steric interactions between the ligands. The reactions of [(MePh2P)2NiCl2] with [7-R-nido-7,8-C2B9H11]− (R = H, Me, Ph) result in nickelacarboranes 3,3-(MePh2P)2-1-R-closo-3,1,2-NiC2B9H10 with noticeable steric loading, while the reaction with [7-(CyNH)2C-nido-7,8-C2B9H11] proceeds with the displacement of one phosphine ligand with the formation of a mixed-ligand phosphine-chloride half-sandwich complex 3-MePh2P-3-Cl-1-(CyNH)2C-closo-3,1,2-NiC2B9H10.

Proton‐Promoted Nickel‐Catalyzed Asymmetric Hydrogenation of Aliphatic Ketoacids

AbstractA robust and highly active homogeneous chiral nickel–phosphine complex for the asymmetric hydrogenation of aliphatic γ‐ and δ‐ketoacids has been discovered. The hydrogenation could proceed smoothly in the presence of 0.0133 mol% catalyst loading (S/C=7500). The coordination chemistry and catalytic behavior of Ni(OTf)2with (S,S)‐Ph‐BPE were explored by1H NMR and HRMS. The mechanistic studies revealed that a proton promoted the activation of the substrate C=O bond and controlled the stereoselectivity through hydrogen bonds. A series of chiral γ‐ and δ‐alkyl substituted lactones were obtained in high yields with excellent enantioselectivities (up to 98 % yield and 99 % ee). In addition, this catalytic system also demonstrated that levulinic acid produced from a biomass feedstock was converted into chiral γ‐valerolactone without loss of ee value.

Proton-Promoted Nickel-Catalyzed Asymmetric Hydrogenation of Aliphatic Ketoacids.

A robust and highly active homogeneous chiral nickel-phosphine complex for the asymmetric hydrogenation of aliphatic γ- and δ-ketoacids has been discovered. The hydrogenation could proceed smoothly in the presence of 0.0133 mol% catalyst loading (S/C=7500). The coordination chemistry and catalytic behavior of Ni(OTf)2 with (S,S)-Ph-BPE were explored by 1 H NMR and HRMS. The mechanistic studies revealed that a proton promoted the activation of the substrate C=O bond and controlled the stereoselectivity through hydrogen bonds. A series of chiral γ- and δ-alkyl substituted lactones were obtained in high yields with excellent enantioselectivities (up to 98 % yield and 99 % ee). In addition, this catalytic system also demonstrated that levulinic acid produced from a biomass feedstock was converted into chiral γ-valerolactone without loss of ee value.

Role of High-Spin Species and Pendant Amines in Electrocatalytic Alcohol Oxidation by a Nickel Phosphine Complex

The development of active and efficient electrocatalysts for oxidation of alcohols using earth-abundant metals will aid progress toward a renewable energy economy. Here, we present a detailed mechanistic study of electrocatalytic benzyl alcohol oxidation by a molecular nickel complex containing pendant amines using a combination of kinetic studies, nuclear magnetic resonance spectroscopy, and density functional theory. The catalyst preferentially binds alcohol in a high-spin octahedral geometry, but this complex is not readily deprotonated by an exogenous base and inhibits catalysis. Dissociation of one or more solvent ligands returns the complex to a low-spin state that can be deprotonated. Kinetic modeling indicates that the off-cycle high-spin intermediate lowers the catalytic turnover frequency by a factor of 8, suggesting that substantial gains in activity can be attained by improvements to the catalyst coordination geometry. In a second finding, we demonstrate that the pendant amine of the catalyst only functions as a proton relay for the potential-determining step, oxidation of a nickel hydride intermediate, but does not have a substantial impact on the overall rate for oxidation of benzyl alcohol to benzaldehyde. This result contradicts the common expectation for pendant amines to participate in rate-limiting proton transfer reactions.

Solvent-free transformation of levulinic acid into valeric acid and its esters using the nickel phosphine complex and metal triflate co-catalytic system

Neat levulinic acid is directly converted to valeric acid under mild conditions. Inexpensive and environmentally friendly non-noble metal catalysts are used.

Coordination Ability of 10-EtC(NHPr)=HN-7,8-C2B9H11 in the Reactions with Nickel(II) Phosphine Complexes

The complexation reactions of nido-carboranyl amidine 10-PrNHC(Et)=HN-7,8-C2B9H11 with different nickel(II) phosphine complexes such as [(PR2R’)2NiCl2] (R = R’ = Ph, Bu; R = Me, R’ = Ph) were investigated. As a result, a series of novel half-sandwich nickel(II) π,σ-complexes [3-R’R2P-3-(8-PrN=C(Et)NH)-closo-3,1,2-NiC2B9H10] with the coordination of the carborane and amidine components was prepared. The acidification of obtained complexes with HCl led to the breaking of the Ni-N bond with formation of nickel(II) π-complexes [3-Cl-3-R’R2P-8-PrNH=C(Et)NH-closo-3,1,2-NiC2B9H10]. The crystal molecular structure of [3-Ph3P-3-(8-PrN=C(Et)NH)-closo-3,1,2-NiC2B9H10] was determined by single crystal X-ray diffraction.

Preparation and stereochemistry of nickel phosphine complexes

The Nickel (II) ion forms many stable complexes as predicted by the Irving Williams series. This experiment is about preparation and stereochemistry of nickel phosphine complexes. The nickel phosphine complexes, which were prepared are NiBr2(PPh3)2 and NiBr2(PCy3)2. The first part of the experiment is to prepare the nickel complexes. After preparing nickel phosphine complexes NiBr2 (PPh3)2 and NiBr2 (PCy3)2, the complexes have been analyzed for structural determination. The complexes were analyzed by the Magnetic Moments of solids-The Johnson Matthey Balance, UV-visible (electronic spectra), Infrared spectra (normal range) and Far-infrared spectra (which were supplied in the practical booklet).

Analysis of the structural determination nickel complexes

The sets of bands in the IR and UV – spectra are the same specific a characteristic of a substance, like a person’s fingerprint. According to these spectra, the substance it can be identified if its vibrational spectrum is already known. In addition, by IR and UV –spectra determine the symmetry and structure of unexplored molecules. Frequencies the main vibrations found from the spectra are necessary for calculating thermodynamic properties of substances. Measuring the intensity of bands in the spectra allows you to quantitative analysis, study chemical equilibria and kinetics of chemical reactions, monitor the progress of technological processes. Nickel (II) ion forms many stable complexes. This work is devoted to the preparation and study of the stereochemistry of nickelphosphine complexes. We obtained nickelphosphine complexes NiBr2(PPh3)2; NiBr2(PCy3)2, and analysed to determine the structure. We studied the magnetic moments of solids from the following spectra in UV-visible (electronic spectra), infrared spectrum (normal range) and far infrared spectrum.

Facile synthesis of a nickel(0) phosphine complex at ambient temperature.

The reaction of the bis(methoxy)-2-pyridyl-phosphine (MeO)2P(2-py) (1) with [Ni(MeCN)6](BF4)2 leads to the unexpected single-step reduction of NiII and the formation of a tetrahedral nickel(0) complex [{(MeO)2P(2-py-H)}2{(MeO)2P(2-py)}2Ni](BF4)2 (2). The redox activity is probably induced by the decomposition of the tetrafluoroborate anion; NMR spectroscopic studies point towards a fluoride-assisted oxidation of the 2-pyridyl-phosphine ligand, with associated reduction of the metal.

A transparent electrode with water-oxidizing activity

Hydrogen production by water splitting is a promising method to store energy. Water-oxidation reaction is a bottleneck in water-splitting systems. Herein, a mononuclear nickel(II) phosphine complex with 1,2-bis(dicyclohexylphosphino)ethane ligand, was synthesized and characterized by X-ray crystallography method. The water-oxidizing catalyst under the electrochemical condition was studied. The role of Ni compound for the water-oxidation reaction on the surface of fluorine-doped tin oxide as one of the true catalysts was investigated by the electrochemical methods and Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) Spectroscopy. The big ligand around the Ni ion causes a very small size of Ni-based particles on the surface of the electrode, which are the active catalysts for the water-oxidation reaction. Such small nanosized Ni-based compounds are transparent and have no effect on the transparency of the obtained fluorine-doped tin oxide. Thus, it is a promising method to synthesize a transparent fluorine-doped tin oxide with water-oxidizing activity.

A nickel phosphine complex as a fast and efficient hydrogen production catalyst.

Here we report the electrocatalytic reduction of protons to hydrogen by a novel S2P2 coordinated nickel complex, [Ni(bdt)(dppf)] (bdt = 1,2-benzenedithiolate, dppf = 1,1'-bis(diphenylphosphino)ferrocene). The catalysis is fast and efficient with a turnover frequency of 1240 s(-1) and an overpotential of only 265 mV for half activity at low acid concentrations. Furthermore, catalysis is possible using a weak acid, and the complex is stable for at least 4 h in acidic solution. Calculations of the system carried out at the density functional level of theory (DFT) are consistent with a mechanism for catalysis in which both protonations take place at the nickel center.

Tandem hydrogenation and condensation of fluorinated α,β-unsaturated ketones with primary amines, catalyzed by nickel.

A simple homogeneous catalytic system based on nickel phosphine complexes has been developed for the transfer hydrogenation and condensation of α,β-unsaturated ketones to yield saturated ones and saturated imines using primary amines as hydrogen donors. Thus, a wide range of fluorinated 1,5-diaryl-1,4-pentadiene-3-ones were allowed to react with substituted benzylamines in the presence of [(dippe)Ni(μ-H)]2 (dippe = 1,2-bis-(diisopropylphosphino)-ethane) using ethanol as a solvent at 180 °C to give the corresponding saturated carbonyl compounds; here hydrogenation of the C[double bond, length as m-dash]C bond was preferred over the C[double bond, length as m-dash]O bond. Under the same reaction conditions but using an excess of benzylamine, a tandem process is then favoured, starting also with the reduction of the C[double bond, length as m-dash]C bond followed by a nucleophilic addition of the primary amine to yield valuable saturated imines with good to excellent yields (62%-91%).

Nickel phosphine catalysts with pendant amines for electrocatalytic oxidation of alcohols.

Nickel phosphine complexes with pendant amines have been found to be electrocatalysts for the oxidation of primary and secondary alcohols, with turnover frequencies as high as 3.3 s(-1). These complexes are the first electrocatalysts for alcohol oxidation based on non-precious metals, which will be critical for use in fuel cells.

Hydrofluoroarylation of Alkynes with Ni Catalysts. C–H Activation via Ligand-to-Ligand Hydrogen Transfer, an Alternative to Oxidative Addition

The mechanism of the hydrofluoroarylation of alkynes, RC≡CR, by nickel phosphine complexes, described by Nakao et al. (Dalton Trans. 2010, 39, 10483), was studied by density functional theory (DFT) calculations. The oxidative addition of a C–H bond of partially fluorinated benzenes, C6FnH6–n (n = 0–5) to a Ni(0) phosphine complex is reversible, but the oxidative addition of a C–F bond yields a stable product via a high-energy barrier. A pathway via the Ni(II) hydride complex is eliminated on the basis of a calculated H/D kinetic isotope effect (KIE) that does not agree with the measured value. An alternate pathway was determined, using as reactant a Ni(phosphine)(alkyne) complex that is shown to be the major species in the reactive media under the catalytic conditions. This pathway is initiated by arene coordination to the Ni alkyne complex followed by proton transfer from the σ-C–H bond of the coordinated arene to the alkyne as the C–H activation step. Analysis of the charge distribution shows that the a...

Transformation of α-Substituted Propanols into γ-Amino Alcohols through Nickel-Catalyzed Amination on the Terminal γ-Carbon of Propanols

A nickel―phosphine complex was found to be effective as the catalyst for the transformation of alcohols into β-enaminones, which was successively converted into γ-amino alcohols by a conventional reductant. The sequential transformation is equivalent to the carbon―nitrogen bond formation at the γ-position of saturated alcohols.

Nickel-catalyzed allylic substitution of simple alkenes.

This report describes a nickel-catalyzed allylic substitution process of simple alkenes whereby an important structural motif, a 1,4-diene, was prepared. The key to success is the use of an appropriate nickel-phosphine complex and a stoichiometric amount of silyl triflate. Reactions of 1-alkyl-substituted alkenes consistently provided 1,1-disubstituted alkenes with high selectivity. Insight into the reaction mechanism as well as miscellaneous application of the developed catalytic process is also documented.

Synthesis, characterisation and crystal structure of a novel nickel(II) phosphine complex, trans-[Ni2Cl4{cis-(Cy2PCH2)2C6H4}2

The reaction of 1,3-C6H4(CH2PCy2)2 with anhydrous nickel(II) chloride in dry THF produces the non-cyclometallated dinuclear complex trans-[Ni2Cl4{cis-(Cy2PCH2)2C6H4}2]. The compound was characterised by 1H, 31P and 13C NMR spectroscopy and its solid state structure was determined by X-ray diffraction. An improved synthetic procedure of the aromatic pincer ligand 1,3-C6H4(CH2PCy2)2 is reported.