Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation

This work demonstrates the dominance of a Ni(0/II/III) cycle for Ni-photoredox amide arylation, which contrasts with other Ni-photoredox C-heteroatom couplings that operate via Ni(I/III) self-sustained cycles. The kinetic data gathered when using different Ni precatalysts supports an initial Ni(0)-mediated oxidative addition into the aryl bromide. Using NiCl₂ as the precatalyst resulted in an observable induction period, which was found to arise from a photochemical activation event to generate Ni(0) and to be prolonged by unproductive comproportionation between the Ni(II) precatalyst and the in situ generated Ni(0) active species. Ligand exchange after oxidative addition yields a Ni(II) aryl amido complex, which was identified as the catalyst resting state for the reaction. Stoichiometric experiments showed that oxidation of this Ni(II) aryl amido intermediate was required to yield functionalized amide products. The kinetic data presented supports a rate-limiting photochemically-mediated Ni(II/III) oxidation to enable C−N reductive elimination. An alternative Ni(I/III) self-sustained manifold was discarded based on EPR and kinetic measurements. The mechanistic insights uncovered herein will inform the community on how subtle changes in Ni-photoredox reaction conditions may impact the reaction pathway, and have enabled us to include aryl chlorides as coupling partners and to reduce the Ni loading by 20-fold without any reactivity loss.     

Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes

Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp³)?C and C(sp³)?O bond‐forming reactions at high‐valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral Ni^IV complex ligated by tris(pyrazolyl)borate and a cationic octahedral Ni^III complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp³)?C(sp²) bond‐forming reductive elimination occurs from both centers, but the Ni^III complex reacts up to 300‐fold faster than the Ni^IV, depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO^?), the Ni^IV complex exclusively undergoes C(sp³)?OAc bond formation, while the Ni^III analogue forms the C(sp³)?C(sp²) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M?C(sp³) bonds, and thus their relative reactivity towards outer‐sphere S_N2‐type bond‐forming reactions.     

Synthesis and Structural Characterization of a Novel Heterodinuclear Vanadium(IV)‐Nickel(II) Complex

A novel V^IV‐Ni^II heterodinuclear complex [VO(cat)₂][Ni(1, 2‐PDA)₂H₂O] ( 1 ) (cat = catechol; 1, 2‐PDA = 1, 2‐propane diamine) was synthesized at low temperature (10 °C) and characterized by IR spectroscopy and X‐ray diffraction. A novel Ni–O=V structure exists in the complex, the vanadyl–catechol moiety and the nickel–diamine moiety are connected by an oxygen bridge; all molecules are further assembled into crystallites by O–H ··· O hydrogen bonds.     

Phosphaniminato-Komplexe von Nickel(II) mit Heterocubanstruktur

Phosphoraneiminato Complexes of Nickel(II) with Heterocubane Structure The phosphoraneiminato complexes [NiBr(NPR₃)]₄ (R = CH₃, C₂H₅) and [NiI(NPEt₃)]₄ were obtained from NiBr₂ and NiI₂, respectively, with excess Me₃SiNPR₃ in the melt (R = CH₃, C₂H₅) in the presence of sodium fluoride. They form dark-green, moisture sensitive crystalline powders. They were characterized by IR spectroscopy, mass spectrometry, magnetic behaviour as well as by crystal structure analyses. The compounds possess heterocubane structures, in which the nickel atoms are linked via μ₃–N-bridges of the phosphoraneiminato groups.     

Two-Dimensional (1)H NMR Studies on Octahedral Nickel(II) Complexes

The dinucleating ligand ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetrakis[(2-(1-ethylbenzimidazoyl)] (EGTB-Et; 1) was used to synthesize the dinuclear Ni(II) tetraacetonitrile complex cation [Ni(2)(EGTB-Et)(CH(3)CN)(4)](2+) (2): triclinic space group P&onemacr; (a = 12.273(5) ?, b = 12.358(7) ?, c = 12.561(6) ?, alpha = 90.43(4) degrees, beta = 110.26(3) degrees, gamma = 99.21 (4) degrees, and Z = 1). The structure shows two identical octahedral Ni(II) centers each bound to two benzimidazole ring nitrogen atoms, one amine nitrogen atom, an ether oxygen atom, and two acetonitrile nitrogen atoms. The Ni(II) ions are tethered together by a diethyl ether linkage with a crystallographic center of inversion between the methylene carbons of this bridge. The Ni--Ni separation in 2 is 7.072 ?. The mononuclear Ni(II) complex cation [Ni(Bipy)(2)(OAc)](+) (3) (Bipy = bipyridine) was synthesized and crystallographically characterized: monoclinic space group P2(1)/c (a = 9.269(4) ?, b = 8.348(4) ?, c = 14.623(7) ?, and beta = 102.46(4) degrees, Z = 2). The Ni(II) ions in 3 adopts a distorted octahedral geometry and is bound to four bipyridine ring nitrogen atoms and two carboxylate oxygen atoms. The average Ni-N and Ni-O distances are 2.062 and 2.110 ?. The electronic absorption spectra of both 2 and 3 were recorded in acetonitrile solution and are consistent with octahedral coordination geometries about the Ni(II) ions with Racah parameters of 840 and 820 cm(-)(1), respectively. Both one- and two-dimensional (1)H NMR techniques were used to assign the observed hyperfine shifted (1)H NMR resonances of 2 and 3 in acetonitrile solution. Clear COSY cross signals are observed between the aromatic protons of both the benzimidazole and pyridine protons of 2 and 3, respectively. The use of 2D NMR methods to assign inequivalent aromatic protons rather than synthetic methods such as substitution or deuteration are discussed.     

Simultaneous Determination of Nickel(II) and Cobalt(II) by Second-Derivative Spectrophotometry

4-(2-Pyridylazo) resorcinol, PAR, is shown to be useful for simultaneous determination of cobalt(II) and nickel(II) using second-derivative spectrophotometric method with controlled experimental parameters. This method allows the determination of 0.20-1.25 ppm of nickel(II) and 0.25-1.50 ppm of cobalt(II) in mixtures with good precision and accuracy. This method has advantages of simplicity, speed and requires no prior separations.     

Nickel(II) 1,10-Phenanthroline complexes: cis-[Aqua(Bromo) bis (1,10-Phenanthroline)Nickel(II)] Bromide Trihydrate and ( tris (1,10-Phenanthroline)Nickel(II)] Bromide Octahydrate

[Ni(phen)₂(H₂O)Br]Br·3H₂O where phen is 1,10-phenanthroline, is a light-blue material which crystallizes in the monoclinic space group P2₁/c with Z = 4, a = 10.4300(4), b = 25.310(2), c = 9.7790(9)?Å and β = 102.932(6)°. The structure was determined at ambient temperature from 5161 reflections with R = 0.0643 and R _w = 0.1306. The structure consists of a complex cation, a bromide anion and three waters of hydration. The Ni atom is pseudo-octahedral with a cis arrangement of Br and H₂O. This cis geometry persists in solution, as evidenced by ¹H NMR spectroscopy, although the Br may be replaced by another H₂O. [Ni(phen)₃]Br₂·8H₂O is a light-red material which crystallizes in the monoclinic space group C2/m with Z = 8, a = 23.6320(11), b = 21.4880(13), c = 15.5470(9)?Å and β = 107.927(3)°. The structure was determined at 120?K from 6820 reflections with R = 0.0733 and R _w = 0.1022. The structure consists of a complex cation, two bromide anions and eight waters of hydration. The anions and waters are extensively disordered. The Ni atom is pseudo-octahedral.     

Synthesis and Characterization of Two Trinuclear Nickel(II) Complexes

Two novel trinuclear nickel(II) complexes have been synthesized and characterized by X‐ray single crystal diffraction. Compound [Ni₃(ashz)₃(py)₂(DMF)₂]·(DMF)₂ ( 1 ) crystallizes in the monoclinic, space group C2/c, with a = 22.114(2), b = 10.509(9), c = 19.485(2) Å, β = 114.443(1)°, Z = 4; compound [Ni₃(acshz)₃(py)₂(DMF)₂]·(DMF)₂ ( 2 ) crystallizes in the monoclinic space group P2₁/n with a = 20.0620(2), b = 9.7017(6), c = 25.0533(2) Å, β = 97.0610(2)°, Z = 4, where ashz and acshz are deprotonated N‐acetylsalicylhydrazide (H₃ashz) and N‐acetyl‐5‐chlorosalicylhydrazide (H₃acshz), respectively. The crystal structure analysis of 1 and 2 showed that three Ni²⁺ ions in a linear arrangement are bridged by two ligands ((ashz)^3? or (acshz)^3?) to form a neutral nuclear with two four‐coordinate square‐planar nickel ions linked by a six‐coordinate octahedral central nickel ion.     

Carbon–Fluorine Reductive Elimination from Nickel(III) Complexes

We report a C−F reductive elimination from a characterized first‐row aryl metal fluoride complex. Reductive elimination from the presented nickel(III) complexes is faster than C−F bond formation from any other characterized aryl metal fluoride complex.     

Study on the Gas Permeability of Nickel(II) Polyurethane Complexes

Ionic polyurethanes (PUs) were prepared from hydroxyl‐terminated polybutadiene (HTPB) and 4,4′‐dicyclohexylmethane diisocyanate (H₁₂MDI) by a two‐stage method. The ionic group was introduced by adding 4,8‐diazaundecanediamide (L‐2,3,2) as the chain extender of which the tertiary amines and carbonyl groups were complexed with nickel ions. It was found that the binding of hard segments and the flexibility of soft segments had subtle effects on the gas permeability. The effects of hard segment content and the amount of nickel ion on the gas permeability and morphological properties were investigated. Fourier transform infrared (FTIR) spectroscopy was utilized to identify the segregation between hard and soft segments and structure change, which affect the transport properties. The hydrogen bonding index (HBI), frequency difference, and shift as a measure of the phase segregation and the average strength of the interpolymer hydrogen bonds were utilized to study the intermolecular interaction and transport property of the prepared PUs. The oxygen and nitrogen permeabilities of membranes were determined by using gas permeability analyzer. The results of FTIR, differential scanning calorimetry and thermogravimetric analysis measurements explain the complexation and, hence, the gas permeability.     

Nickel Tetracarbonyl as Starting Material for the Synthesis of NHC-stabilized Nickel(II) Allyl Complexes

A novel, useful in situ synthesis for NHC nickel allyl halide complexes [Ni(NHC)(η³-allyl)(X)] starting from [Ni(CO)₄], NHC and allyl halides is presented. The reaction of [Ni(CO)₄] with (i) one equivalent of the corresponding NHC and (ii) with an excess of the corresponding allyl chloride at room temperature leads with elimination of carbon monoxide to complexes of the type [Ni(NHC)(η³-allyl)(X)]. This approach was used to synthesize the complexes [Ni(tBu₂Im)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 2 ), [Ni(iPr₂Im^Me)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 3 ), [Ni(iPr₂Im)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 4 ), [Ni(iPr₂Im)(η³-H₂C -C (H)-C (Me)₂)(Br)] ( 5 ), [Ni(Me₂Im^Me)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 6 ), and [Ni(EtiPrIm^Me)(η³-H₂C -C (Me)-C H₂)(Cl)] ( 7 ). The complexes 1 to 7 were characterized using NMR and IR spectroscopy and elemental analysis, and the molecular structures are provided for 2 and 7 . The allyl nickel complexes 1 – 7 are stereochemically non-rigid in solution due to (i) NHC rotation about the nickel-carbon bond, (ii) allyl rotation about the Ni–η³-allyl axis and (iii) π–σ–π allyl isomerization processes. The allyl halide complexes can be methylated as was demonstrated by the methylation of a number of the complexes [Ni(NHC)(η³-allyl)(X)] with methylmagnesium chloride or methyllithium, which led to isolation of the complexes [Ni(Me₂Im)(η³-H₂C -C (Me)-C H₂)(Me)] ( 8 ), [Ni(tBu₂Im)(η³-H₂C -C (Me)-C H₂)(Me)] ( 9 ), [Ni(iPr₂Im^Me)(η³-H₂C -C (Me)-C H₂)(Me)] ( 10 ), [Ni(iPr₂Im)(η³-H₂C -C (Me)-C H₂)(Me)] ( 11 ), [Ni(iPr₂Im)(η³-H₂C -C (H)-C (Me)₂)(Me)] ( 12 ), and [Ni(EtiPrIm^Me)(η³-H₂C -C (Me)-C H₂)(Me)] ( 13 ). These complexes were fully characterized including X-ray molecular structures for 10 and 11 .     

Nickel(II) di(pentyl)dithiocarbamates with P ligands

Ni(II) di(pentyl)dithiocarbamates of composition [Ni(Pe₂dtc)₂], [NiX(Pe₂dtc)(PPh₃)] (X = Cl, Br, I, NCS), [Ni(NCS)(Pe₂dtc)(PBut₃)], [Ni(Pe₂dtc)(PPh₃)₂]ClO₄ and [Ni(Pe₂dtc)(PPh₃)₂]PF₆ (Pe₂dtc = di(pentyl)dithio-carbamate, PPh₃ = triphenylphosphine, PBut₃ = tributylphosphine) have been synthesized. The complexes have been characterized by the usual methods. X-ray structure analyses confirmed the nature of [NiI(Pe₂dtc)(PPh₃)] and [Ni(Pe₂dtc)(PPh₃)₂]ClO₄ complexes.