Air-stable Nickel Research Articles

Nickel Phosphite/Phosphine-Catalyzed C-S Cross-Coupling of Aryl Chlorides and Thiols.

A method for the coupling of aryl chlorides and thiophenols using an air-stable nickel(0) catalyst is described. This thioetherification procedure can be effectively applied to a range of electronically diverse aryl/heteroaryl chlorides without more expensive metal catalysts such as palladium, iridium, or ruthenium. This investigation also illustrates both, a variety of thiol coupling partners and, in certain cases, the use of Cs2CO3.

Air-Stable α-Diimine Nickel Precatalysts for the Hydrogenation of Hindered, Unactivated Alkenes

Treatment of a mixture of air-stable nickel(II) bis(octanoate), Ni(O2CC7H15)2, and α-diimine ligand, iPrDI or CyADI (iPrDI = [2,6-iPr2–C6H3N═C(CH3)]2, CyADI = [C6H11N═C(CH3)]2) with pinacolborane (HBPin) generated a highly active catalyst for the hydrogenation of hindered, essentially unfunctionalized alkenes. A range of tri- and tetrasubstituted alkenes was hydrogenated and a benchtop procedure for the hydrogenation of 1-phenyl-1-cyclohexene on a multigram scale was demonstrated and represents an advance in catalyst activity and scope for the nickel-catalyzed hydrogenation of this challenging class of alkenes. Deuteration of 1,2-dimethylindene with the in situ-generated nickel catalyst with iPrDI exclusively furnished the 1,2-syn-d2-dimethylindane. With cyclic trisubstituted alkenes, such as 1-methyl-indene and methylcyclohexene, deuteration with the in situ generated nickel catalyst under 4 atm of D2 produced multiple deuterated isotopologues of the alkanes, signaling chain running processes that are co...

Nickel-Catalyzed Cross-Coupling of Ammonia or Primary Alkylamines with (Hetero)aryl Sulfamates, Carbamates, or Pivalates

A catalyst system capable of effecting the cross-coupling of ammonia or primary alkylamines with (hetero)aryl sulfamates, carbamates, or pivalates is reported for the first time. The air-stable nickel(II) pre-catalyst C1 tolerates a broad spectrum of heterocyclic functionality within both reaction partners, as well as ether, nitrile, pyrrole, trifluoromethyl, and boronate ester substituents. In the case of reactions involving primary alkylamines and (hetero)aryl sulfamates and carbamates, room-temperature cross-couplings were achieved.

Discrete Air-Stable Nickel(II)–Palladium(II) Complexes as Catalysts for Suzuki–Miyaura Reactions

Four novel bidentate phosphine-Pd complexes coordinated by NiN2S2 metallodithiolate ligands were synthesized and characterized, including XRD analysis; these redox-active complexes are stable in air, and they survive column chromatography on silica gel. The Ni–Pd bimetallic complexes are demonstrated to be precatalyst for Suzuki–Miyaura cross-coupling reactions. The best of these has an overall yield of over 99% under only 1% catalyst loading. The role of NiN2S2 as a stabilizing bidentate ligand that is also oxidizable may account for its efficacy in the support of the catalysis.

A room temperature cyanation of (hetero)aromatic chlorides by an air stable nickel(ii) XantPhos precatalyst and Zn(CN)2.

A methodology for the synthesis of (hetero)aromatic nitriles from aryl chlorides at room temperature has been developed. This methodology uses an air and moisture stable nickel(ii) XantPhos precatalyst and Zn(CN)2 as the cyanide (CN-) source.

Alkene Hydrosilylation Using Tertiary Silanes with α-Diimine Nickel Catalysts. Redox-Active Ligands Promote a Distinct Mechanistic Pathway from Platinum Catalysts

Combination of the readily available α-diimine ligand, ((ArN═C(Me))2 Ar = 2,6-iPr2–C6H3), (iPrDI) with air-stable nickel(II) bis(carboxylates) generated a highly active catalyst exhibiting anti-Markovnikov selectivity for the hydrosilylation of alkenes with a variety of industrially relevant tertiary alkoxy- and siloxy-substituted silanes. A combination of the method of continuous variations with stoichiometric studies identified the formally Ni(I) hydride dimer, [(iPrDI)NiH]2 as the nickel compound formed following reduction of the carboxylate ligands. For the hydrosilylation of 1-octene with (EtO)3SiH, a rate law of [Ni]1/2[1-octene][(EtO)3SiH] in combination with deuterium-labeling studies establish dissociation of the nickel hydride dimer followed by fast and reversible alkene insertion into (iPrDI)NiH, consistent with turnover-limiting C–Si bond formation. The hydrosilylation of 1-octene with triethoxysilane, a reaction performed commercially in the silicones industry on a scale of >5 000 000 kg/year...

ChemInform Abstract: Nickel‐Catalyzed Synthesis of Enamides and Enecarbamates via Isomerization of Allylamides and Allylcarbamates.

A single-component, air-stable nickel precatalyst can catalyze the isomerization of allylamides for the synthesis of enamides. The scope of the reaction encompasses various substituted allylamides and allylcarbamates as well as homoallylamides. The reaction can be performed on a multigram-scale without specialized glove-box equipment or Schlenk techniques.

Air-stable nickel precatalysts for fast and quantitative cross-coupling of aryl sulfamates with aryl neopentylglycolboronates at room temperature.

A library containing 10 air-stable Ni(II)X(Aryl)(PCy3)2 σ-complexes as precatalysts (X = Cl, Br, OTs, OMs, aryl = 1-naphthyl, 2-naphthyl; X = Cl, 1-acenaphthenyl, 1-(2-methoxynaphthyl), 9-phenanthrenyl, 9-anthracyl) was synthesized and demonstrated to quantitatively cross-couple 2-methoxyphenyl dimethylsulfamate with methyl 4-(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)benzoate at 23 °C in dry THF in the presence of K3PO4(H2O)3.2 in less than 60 min. Lower or higher amounts of H2O in K3PO4 and as received THF mediate the same transformation in a maximum three times longer reaction time.

Facile and Room-Temperature Activation of Csp3–Cl Bonds by Cheap and Air-Stable Nickel(II) Complexes of (N-Thioether) DPPA-Type Ligands

Reaction of the diphosphine (P,P) ligand N(PPh2)2(n-PrSMe) (1) or N(PPh2)2(p-(SMe)C6H4) (2) with [Ni(NCMe)6][BF4]2 in a 2:1 molar ratio afforded the bis-chelated, dicationic Ni(II) complexes [Ni(1)2][BF4]2 (3) and [Ni(2)2][BF4]2 (4), respectively. Both complexes were characterized in solution by various spectroscopic techniques and in the solid state by X-ray diffraction studies. In the presence of Zn metal used as cheap reductant, complexes 3 and 4 activate the inert C–Cl bonds of dichloromethane at room temperature to afford in high yield the phosphonium ylide derivatives [Ni((Ph2P)N{P(CH2)Ph2}(n-PrSMe)-P,C)2][BF4]2 (5) and [Ni((Ph2P)N{P(CH2)Ph2}(p-(SMe)C6H4)-P,C)2][BF4]2 (6), respectively. The formation of [Ni((Ph2P)N{P(CH2)Ph2}(n-PrSMe)-P,C)2]Cl2 (5′), an analogue of complex 5, from a Ni(0) precursor supports the reduction of the Ni(II) precursors by the Zn reagent prior to C–Cl bond activation. The structures of 5 and 5′ were unambiguously established by X-ray diffraction analysis.

Highly regioselective nickel-catalyzed cross-coupling of N-tosylaziridines and alkylzinc reagents.

Herein, we report the first ligand-controlled, nickel-catalyzed cross-coupling of aliphatic N-tosylaziridines with aliphatic organozinc reagents. The reaction protocol displays complete regioselectivity for reaction at the less hindered C-N bond, and the products are furnished in good to excellent yield for a broad selection of substrates. Moreover, we have developed an air-stable nickel(II) chloride/ligand precatalyst that can be handled and stored outside a glovebox. In addition to increasing the activity of this catalyst system, this also greatly improves the practicality of this reaction, as the use of the very air-sensitive Ni(cod)2 is avoided. Finally, mechanistic investigations, including deuterium-labeling studies, show that the reaction proceeds with overall inversion of configuration at the terminal position of the aziridine by way of aziridine ring opening by Ni (inversion), transmetalation (retention), and reductive elimination (retention).

Controlled Living Polymerization of Carbodiimides Using Versatile, Air-Stable Nickel(II) Initiators: Facile Incorporation of Helical, Rod-like Materials

The new polymerization of carbodiimides using two, simple [bis(triphenylphosphino)aryl]nickel(II) bromide complexes has been discovered to occur in a controlled, living fashion. These initiators are substantially more air and moisture stable compared to their titanium(IV) counterparts making them significantly easier to synthesize, purify, and utilize. The polymerization is initiated via aryl ligand transfer to the electrophilic center carbon of the carbodiimide. Sequential insertions of the carbodiimide π-bond into the nickel–nitrogen amidinate coordination bond propagates the polymer chain in a living chain growth manner as evident by the linear relationship in the plots of percent conversion vs Mn, ln([M]o/[M]) vs time, and monomer: initiator ratio vs Mn. The transferred aryl ligand was confirmed to be appended to the terminus of the polymer chain by MALDI–TOF and 19F NMR. This added control element offers new opportunities to end functionalize rigid-rod, helical polycarbodiimides. This new technique a...

ChemInform Abstract: Development of an Air‐Stable Nickel Precatalyst for the Amination of Aryl Chlorides, Sulfamates, Mesylates, and Triflates.

A new air-stable nickel precatalyst for C–N cross-coupling is reported. The developed catalyst system displays a greatly improved substrate scope for C–N bond formation to include both a wide range of aryl and heteroaryl electrophiles and aryl, heteroaryl, and alkylamines. The catalyst system is also compatible with a weak base, allowing the amination of substrates containing base-sensitive functional groups.

A Broadly Applicable Strategy for Entry into Homogeneous Nickel(0) Catalysts from Air-Stable Nickel(II) Complexes.

A series of air-stable nickel complexes of the form L2Ni(aryl) X (L = monodentate phosphine, X = Cl, Br) and LNi(aryl)X (L = bis-phosphine) have been synthesized and are presented as a library of precatalysts suitable for a wide variety of nickel-catalyzed transformations. These complexes are easily synthesized from low-cost NiCl2·6H2O or NiBr2·3H2O and the desired ligand followed by addition of 1 equiv of Grignard reagent. A selection of these complexes were characterized by single-crystal X-ray diffraction, and an analysis of their structural features is provided. A case study of their use as precatalysts for the nickel-catalyzed carbonyl-ene reaction is presented, showing superior reactivity in comparison to reactions using Ni(cod)2. Furthermore, as the precatalysts are all stable to air, no glovebox or inert-atmosphere techniques are required to make use of these complexes for nickel-catalyzed reactions.

Development of an air-stable nickel precatalyst for the amination of aryl chlorides, sulfamates, mesylates, and triflates.

A new air-stable nickel precatalyst for C-N cross-coupling is reported. The developed catalyst system displays a greatly improved substrate scope for C-N bond formation to include both a wide range of aryl and heteroaryl electrophiles and aryl, heteroaryl, and alkylamines. The catalyst system is also compatible with a weak base, allowing the amination of substrates containing base-sensitive functional groups.

Sponge‐like Nickel and Nickel Nitride Structures for Catalytic Applications

A safe and simple method to fabricate air-stable nickel nitride and nickel embedded in carbon and nitrogen matrix, with high surface area for catalytic applications, is presented. The new synthesis employs molten inorganic salts as the reaction media. The use of salt melt opens new possibilities for safe, simple, and cheap synthesis of metal nitrides and metals for energy-related applications.

Simplifying Nickel(0) Catalysis: An Air-Stable Nickel Precatalyst for the Internally Selective Benzylation of Terminal Alkenes

The synthesis and characterization of the air-stable nickel(II) complex trans-(PCy(2)Ph)(2)Ni(o-tolyl)Cl is described in conjunction with an investigation of its use for the Mizoroki-Heck-type, room temperature, internally selective coupling of substituted benzyl chlorides with terminal alkenes. This reaction, which employs a terminal alkene as an alkenylmetal equivalent, provides rapid, convergent access to substituted allylbenzene derivatives in high yield and with regioselectivity greater than 95:5 in nearly all cases. The reaction is operationally simple, can be carried out on the benchtop with no purification or degassing of solvents or reagents, and requires no exclusion of air or water during setup. Synthesis of the precatalyst is accomplished through a straightforward procedure that employs inexpensive, commercially available reagents, requires no purification steps, and proceeds in high yield.

Ni(iPr2Im)2Br2]: A Convenient Entry into NHC Nickel ­Chemistry

AbstractThe reaction of the NHC iPr2Im [NHC=N‐heterocyclic carbene, iPr2Im = 1, 3‐bis(isopropyl)imidazolin‐2‐ylidene] with freshly prepared NiBr2 in thf or dme results in the formation of the air stable nickel(II) complex trans‐[Ni(iPr2Im)2Br2] (2). Complex 2 was structurally characterized. Thermal analysis (DTA/TG) reveals a very high decomposition temperature of 298 °C. Reduction of 2 with sodium or C8K in the presence of the olefins COD (cyclooctadiene) or COE (cyclooctene) affords the highly reactive compounds [Ni2(iPr2Im)4(COD)] (1) and [Ni(iPr2Im)2(COE)] (4). Alkylation of 2 with organolithiums leads to the formation of trans‐[Ni(iPr2Im)2(R)2] [R = Me (5), CH2SiMe3 (6)], whereas the reaction of 2 with LiCp* [Cp* = (η5‐C5(CH3)5)] at 80 °C causes the loss of one NHC ligand and affords [(η5‐C5(CH3)5)Ni(iPr2Im)Br] (7).

An Efficient Nickel Catalyst for the Reduction of Carbon Dioxide with a Borane

Nickel hydride with a diphosphinite-based ligand catalyzes the highly efficient reduction of CO(2) with catecholborane, and the hydrolysis of the resulting methoxyboryl species produces CH(3)OH in good yield. The mechanism involves a nickel formate, formaldehyde, and a nickel methoxide as different reduced stages for CO(2). The reaction may also be catalyzed by an air-stable nickel formate.

Nickel-Catalyzed Suzuki-Miyaura Coupling of Aryl Carbamates, Carbonates, and Sulfamates

Efficient Suzuki-Miyaura cross-coupling of aryl carbamates, carbonates, and sul­famates was implemented. The reaction proceeds with moderate to good yields at elevated temperatures using an air-stable nickel(II) catalyst.

The Scope and Limitation of Nickel-Catalyzed Aminocarbonylation of Aryl Bromides from Formamide Derivatives

Nickel-catalyzed aminocarbonylation of aryl halides is described. A well-defined air-stable nickel-phosphite catalytic system (Ni(OAc)(2).4H(2)O/phosphite 1) effectively promoted the aminocarbonylation of aryl bromides with a range of formamides to give the corresponding aryl amide products in moderate to good yields. The less hindered formamide required lower catalytic loading for full conversion and produced higher yields than the more hindered one. It also exhibited base-dependent activity toward formamides.