- Nickel(0)-catalyzed [2 + 2] annulation of electron-deficient allenes. Highly regioselective synthesis of cyclobutanes
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The nickel-catalyzed [2 + 2] annulations of electron-deficient allenes proceed efficiently in a highly regioselective manner under very mild conditions to give the head-to-head cyclodimerization products, bismethylenecyclobutanes, as single isomers in good to fair yields. We also carried out the stoichiometric reaction of these allenes in the presence of Ni(0) complexes and elucidated the mechanism of this highly selective reaction.
- Saito,Hirayama,Kabuto,Yamamoto
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Read Online
- Dehydrogenative coupling of styrene with trisubstituted silanes catalyzed by nickel complexes
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Trisubstituted silanes, e.g., Me,.(EtO)(3-n)SiH (where n = 0-2) and Me2PhSiH in the presence of nickel complexes, e.g., [Ni(acac)2] and [Ni(cod)2], undergo two reactions of dehydrogenative silylation of styrene to yield in
- Marciniec, Bogdan,Maciejewski, Hieronim,Kownacki, Ireneusz
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Read Online
- Tandem Nickel-Catalyzed Dimerization/(4+2) Cycloaddition of Terminal Alkynes with Four-Membered Ring Ketones
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Controlling the behavior of terminal alkynes in metal-catalyzed intermolecular tandem reactions is a formidable challenge despite the potential advantage offered by these strategies in modern synthesis. Herein, we describe that a nickel catalyst enables a tandem process involving the rapid dimerization of terminal alkynes into 1,3-enynes and the cycloaddition of these intermediates with an azetidinone, an oxetanone or benzocyclobutenones. Significantly, the slow or sequential addition of reagents and catalysts is not required to orchestrate their reactivity. These results are in stark contrast with previous cycloadditions of terminal alkynes with strained four-membered ring substrates, which previously led to oligomerization or cyclotrimerization, except in the case of tert-butylacetylene.
- Barday, Manuel,Nicolas, Eva,Higginson, Bradley,Delmotte, Fran?ois,Appelmans, Martin,A?ssa, Christophe
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p. 1081 - 1090
(2021/12/02)
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- Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base
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Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp3)-H arylation with iodoarenes were carried out, to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes undergo the key C-H activation step. The ubiquitous base Na2CO3is found to hinder catalysis; replacement of Na2CO3with NaOtBu gave improved catalytic turnovers under milder conditions. Deprotonation of the 8-aminoquinoline derivativeN-(quinolin-8-yl)pivalamide (1a) at the amide nitrogen using NaH, followed by reaction with NiCl2(PPh3)2allowed for the isolation of complex Ni([AQpiv]-κN,N)2(3) with chelating N-donors (where [AQpiv] = C9NH6NCOtBu). Complex3is a four-coordinate disphenoidal high-spin Ni(II) complex, excluding short anagostic Ni-tBu hydrogen interactions. Complex3reacts with the paddle-wheel [Ph3PNi(μ-CO2tBu)2]2(6·PPh3) ortBuCO2H to give insoluble {[AQpiv]Ni(O2CtBu)}2(5). Dissolution of5in donor solvents L (L= DMSO and DMF) gave a paramagnetic intermediate assigned by NMR as [AQpiv]Ni(O2CtBu)L (5·L) and equilibrium reformation of3and6·L. DFT calculations support this equilibrium in solution. Both3and5undergo C-H activation at temperatures as low as 80 °C and in the presence of PR3(PR3= PPh3, PiBu3) to give Ni(C9NH6NCOCMe2CH2-κN,N,C)PR3(7·PR3). The C-H functionalization reaction orders with respect to7·PiBu3, iodoarenes, and phosphines were determined. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C-H functionalization step; DFT calculations were also carried out to support this finding. When Na2CO3is used as the base, the rate determination step for C-H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR-inactive low-energy off-cycle resting state in catalysis. Replacement of Na2CO3with NaOtBu improved catalysis at milder conditions and made carboxylic acid and phosphine additives unnecessary. Complex3and its functionalized analogues were observed as the catalyst resting state under these conditions.
- Liu, Junyang,Johnson, Samuel A.
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supporting information
p. 2970 - 2982
(2021/06/28)
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- Diboron-Promoted Reduction of Ni(II) Salts: Precatalyst Activation Studies Relevant to Ni-Catalyzed Borylation Reactions
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The activation and reduction of nickel(II) salts under conditions relevant to Ni-catalyzed borylation reactions is reported. Methanolic solutions of NiCl2·6H2O reacted with >2 equiv of (iPr)2NEt were converted to polymeric Ni(OMe)2, which was characterized by IR spectroscopy, magnetic susceptibility measurements, and verified by independent synthesis from NaOMe. When diboron reagents such as bis(neopentylglycolato) diboron (B2(npg)2) were exposed to methanolic solutions of Ni(II) salts and (iPr)2NEt, nickel metal was deposited along with the evolution of hydrogen gas. A direct relationship between yield of nickel metal and equivalents of B2(npg)2 relative to [Ni] was also observed, reaching >99% yield at 8 equiv. Ni(0) coordination complexes were also isolated when a phosphine, phosphite, and/or diene ligand was present, all starting from NiCl2·6H2O, including the following: Ni[P(OPh)3]4 (74% yield), Ni[P(OiPr)3]4 (54% yield), Ni(PPh3)4 (75% yield), (dppp)2Ni + Ni(1,5-cod)2 (dppp = 1,3-bis(diphenylphosphine)propane) (91% yield), Ni(1,5-cod)2 (1,5-cod = 1,5-cyclooctadiene) (69% yield), and (dppf)Ni(1,5-cod) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) (84% yield). The high yields observed indicated the efficient reduction of Ni(II) to Ni(0) and a likely route for precatalyst entry into the Ni-borylation catalytic cycle. These in situ reduction conditions were also successfully applied to a previously developed Ni-catalyzed alpha-arylation reaction where the requisite Ni(1,5-cod)2 precatalyst was substituted for NiCl2·6H2O and catalytic diboron. Comparable yields to the original report were observed under these conditions, further demonstrating that Ni(0) active species can be efficiently accessed with diboron reagents under protic conditions from Ni(II) salt hydrates.
- Joannou, Matthew V.,Sarjeant, Amy A.,Wisniewski, Steven R.
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p. 2691 - 2700
(2021/08/20)
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- AIR-STABLE NI(0)-OLEFIN COMPLEXES AND THEIR USE AS CATALYSTS OR PRECATALYSTS
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The present invention relates to air stable, binary Ni(0)-olefin complexes and their use in organic synthesis.
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Page/Page column 24
(2021/02/05)
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- Reactions of the Ni(0) Compound Ni(PPh3)4 with Unactivated Alkyl Halides: Oxidative Addition Reactions Involving Radical Processes and Nickel(I) Intermediates
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Reactions of the nickel(0) compound NiL4 (L = PPh3) with alkyl halides RX involve initial inner-sphere halogen atom abstraction from the alkyl halides to form alkyl radicals R· and halonickel(I) metalloradical species NiX(PPh3)2,3. The radical pairs then undergo combination within the solvent cage to give the square planar nickel(II) compounds NiRX(PPh3)2. Radical intermediacy is demonstrated persuasively by observations that the relative rates vary in the orders tert-butyl > sec-butyl > n-butyl and RI > RBr > RCl, while density functional theory calculations indicate that the radical mechanism provides a lower energy pathway than do alternative, more conventional pathways. The product of the reaction of Ni(PPh3)4 with methyl iodide, NiMeI(PPh3)2, decomposes in solution to ethane and NiI(PPh3)2,3, but when RX = EtI, n-BuI, sec-BuI, tert-BuI, the alkyl-nickel products undergo rapid β-hydrogen elimination to give the hydride NiHI(PPh3)2 plus the corresponding alkene(s). Reactions also occur in which a portion of the alkyl radicals diffuses from the solvent cage and abstracts hydrogen from NiHI(PPh3)2 to form alkanes RH and Ni(I) species NiI(PPh3)2. As a result, NiHI(PPh3)2 is invariably a minor product while the major products are alkanes RH, alkenes R-H, and NiI(PPh3)2. Hydride NiHI(PPh3)2 is found to decompose to H2 and NiI(PPh3)2 but is stable at low temperatures where it exhibits unusual NMR behavior because of exchange involving free PPh3 and the bis- and trisphosphine species, NiHI(PPh3)2 and NiHI(PPh3)3. Present in all of the reactions are paramagnetic, substitution-labile Ni(I) metalloradical species. As a result, resonances of PPh3, ethylene, and the smaller iodoalkenes are generally broad and shifted because of exchange between free and coordinated ligands.
- Kehoe, Ryley,Mahadevan, Markshun,Manzoor, Adeela,McMurray, Gillian,Wienefeld, Patrick,Baird, Michael C.,Budzelaar, Peter H. M.
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p. 2450 - 2467
(2018/08/21)
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- Catalysis of Cross-Coupling and Homocoupling Reactions of Aryl Halides Utilizing Ni(0), Ni(I), and Ni(II) Precursors; Ni(0) Compounds as the Probable Catalytic Species but Ni(I) Compounds as Intermediates and Products
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Both Ni(0) and Ni(I) compounds are believed to exhibit cross-coupling catalytic properties under various conditions, and the compounds Ni(PPh3)4 and NiCl(PPh3)3 are compared as catalysts for representative Suzuki-Miyaura and Heck-Mizoroki cross-coupling reactions. The Ni(0) compound exhibits catalytic activities, for cross-coupling of chloro and bromoanisole with phenylboronic acid and of bromobenzene with styrene, yielding results which are comparable with those of many palladium-based catalysts, but our findings with NiCl(PPh3)3 are at this point unclear. It seems to convert to catalytically active Ni(0) species under Suzuki-Miyaura reaction conditions and is ineffective for Heck-Mizoroki cross-coupling. The paramagnetic Ni(I) compounds NiX(PPh3)3 (X = Cl, Br, I) are characterized for the first time by 1H NMR spectroscopy and are found to exhibit broad meta and para resonances at δ 9-11 and 3-4, respectively, and very broad ortho resonances at δ 46; these resonances are very useful for detecting Ni(I) species in solution. The chemical shifts of NiCl(PPh3)3 vary with the concentration of free PPh3, with which it exchanges, and are also temperature-dependent, consistent with Curie law behavior. The compound trans-NiPhCl(PPh3)2, the product of oxidative addition of chlorobenzene to Ni(PPh3)4 and a putative intermediate in cross-coupling reactions of chlorobenzene, is found during the course of this investigation to exhibit entirely unanticipated thermal lability in solution in the absence of free PPh3. It readily decomposes to biphenyl and NiCl(PPh3)2 in a reaction relevant to the long-known but little-understood nickel-catalyzed conversion of aryl halides to biaryls. Ni(I) and biphenyl formation is initiated by PPh3 dissociation from trans-NiPhCl(PPh3)2 and formation of a dinuclear intermediate, a process which is now better defined using DFT methodologies.
- Manzoor, Adeela,Wienefeld, Patrick,Baird, Michael C.,Budzelaar, Peter H.M.
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p. 3508 - 3519
(2017/10/03)
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- An improved and efficient synthesis of pinene based bipyridyldiols and bipyridine
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An improved and efficient synthesis of pinene based two bipyridyldiols and bipyridine is reported. For the first time, the sealed tube-pressure reaction of pinene based pyridone with phosphoryl chloride produced an excellent yield (95%) of pinene based 2-chloropyridine, which renders synthesizing pinene based bipyridyldiols a highly inexpensive and high yielding process. Moreover, highly effective reaction condition was developed for homocoupling of chloropyridine with Ni(0) that afforded pinene based bipyridine in a high yield (84%). These newly demonstrated sealed tube-pressure chlorination and homocoupling reaction of chloropyridine afford extremely effect route for the synthesis of pinene based bipyridine.
- Boobalan, Ramalingam,Chen, Chinpiao
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supporting information
p. 1930 - 1934
(2016/04/19)
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- Tandem redox mediator/Ni(II) trihalide complex photocycle for hydrogen evolution from HCl
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Photoactivation of M-X bonds is a challenge for photochemical HX splitting, particularly with first-row transition metal complexes because of short intrinsic excited state lifetimes. Herein, we report a tandem H2 photocycle based on combination of a non-basic photoredox phosphine mediator and nickel metal catalyst. Synthetic studies and time-resolved photochemical studies have revealed that phosphines serve as photochemical H-atom donors to Ni(II) trihalide complexes to deliver a Ni(I) centre. The H2 evolution catalytic cycle is closed by sequential disproportionation of Ni(I) to afford Ni(0) and Ni(II) and protolytic H2 evolution from the Ni(0) intermediate. The results of these investigations suggest that H2 photogeneration proceeds by two sequential catalytic cycles: a photoredox cycle catalyzed by phosphines and an H2-evolution cycle catalyzed by Ni complexes to circumvent challenges of photochemistry with first-row transition metal complexes.
- Hwang, Seung Jun,Powers, David C.,Maher, Andrew G.,Nocera, Daniel G.
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p. 917 - 922
(2015/02/05)
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- 2-Pyridyl-phosphine and -diphosphine complexes of nickel(0), their reactivity (including aqueous solution chemistry), and some related, incidental methylphosphonium iodides
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The chemistry of Ni0-dicarbonyl(pyridylphosphine) complexes of the type Ni(CO)2L2, where L is either P-bonded PPh3-npyn (n = 1-3, py = 2-pyridyl; abbreviated PNx, x = 1-3, species 1a-c), or L2 is (P-P)-chelated py2P(CH2)2Ppy2 or, is further developed from earlier studies by our group [the P-P ligands are abbreviated, respectively, as d(py)pe and d(py)pcp]. The complexes are synthesized from C6H6 solutions of Ni(CO)2(PPh3)2, and the Ni(CO)2(PPh3)(PNx) intermediates (1a-c) are detected; Ni(CO)2[d(py)pcp] (2b) is shown by X-ray analysis to have a distorted tetrahedral structure; and the NiII species [Ni2(CO)4(μ-PN2)2]Cl4 is isolated from a light-induced reaction in CDCl3 solution. Complex 2b dissolves in water at ambient conditions via a net double protonation of pyridyl N-atoms, the {Ni(CO)2[2H-d(py)pcp]}2+ being isolated as the bis(triflate) salt; the dication decomposes in minutes with formation of [Ni(H2O)6]2+, CO, the phosphine dioxide, and deprotonated d(py)pcp. Some twenty-two Ni0 complexes, exemplified by Ni(P-P)2, Ni(PNx)2(P-P), Ni(PNx)4, and related PPh3- and Ph2P(CH2)2PPh2 (dppe)-containing species, are synthesized from Ni(1,5-COD)2 and their reactivity studied; for example, oxidative addition of MeI generates trans-Ni(Me)(I)(PN3)2 and trans-Ni(Me)(I)(P-P)2 but, with non-pyridyl containing reactants such as Ni(PPh3)4 and Ni(dppe)2, only (monomethyl)phosphonium iodides are formed. Such iodides, and the bis(methyl) analogues [(CH3)2(diphosphine)]I2, are then studied for clarification of some observed Ni chemistry. The NMR trends (a)-(d) are noted within the series of Ni0 complexes, and are rationalized: (a) the 2JPP values in 1a-c, and the separation between the two doublets, parallel the number of N-atoms present; (b) the 31P{1H} signals in the Ni(PNx)4 and Ni(PNx)2(P-P) complexes shift downfield in the order PN1 2 3 within linear dependences; (c) the 2JPP values for the Ni(PR3)2(P-P) complexes (R = Ph and PNx) decrease in the order R = Ph > PN1 > PN2 > PN3; (d) and the separation between the two 31P{1H} triplets of the Ni(PNx)2(P-P) complexes generally depends on the relative numbers of phenyl and pyridyl groups.
- Le Page, Matthew D.,Patrick, Brian O.,Rettig, Steven J.,James, Brian R.
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p. 276 - 288
(2015/06/02)
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- SHOP-type nickel complexes with alkyl substituents on phosphorus, synthesis and catalytic ethylene oligomerization
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The β-keto phosphorus ylides (n-Bu)3P=CHC(O)Ph 6, (t-Bu)2PhP=CHC(O)Ph 7, (t-Bu)Ph2P=CHC(O)Ph 8, (n-Bu) 2PhP=CHC(O)Ph 9, (n-Bu)Ph2P=CHC(O)Ph 10, Me 2PhP=CHC(O)Ph 11 and Ph3P=CHC(O)(o-OMe-C6H 4) 12 have been synthesized in 80-96% yields. The Ni(ii) complexes [N=iPh{Ph2PCHC(O=)(o-OMeC6H4)}(PPh 3)] 13, [N=iPh{Ph(t-Bu)PCHC(O=)Ph}(PPh3)] 15, [N=iPh{(n-Bu)2PCHC(O=)Ph}(PPh3)] 16 and [N=iPh{Ph(n-Bu)PCHC(O=)Ph}(PPh3)] 17 have been prepared by reaction of equimolar amounts of [Ni(COD)2] and PPh3 with the β-keto phosphorus ylides 12 or 8-10, respectively, and characterized by 1H and 31P{1H} NMR spectroscopy. NMR studies and the crystal structure determination of 13 indicated an interaction between the hydrogen atom of the C-H group α to phosphorus and the ether function. The complexes [N=iPh{Ph2PCHC(O=)Ph}(Py)] 18, [N=iPh{Ph(t-Bu)PCHC(O=) Ph}(Py)] 19, [N=iPh{(n-Bu)2PCHC(O=)Ph}(Py)] 20, [N=iPh{Ph(n-Bu) PCHC(O=)Ph}(Py)] 21 and [N=iPh{Me2PCHC(O=)Ph}(Py)] 22 have been isolated from the reactions of [Ni(COD)2] and an excess of pyridine with the β-keto phosphorus ylides Ph3PCH=C(O)Ph 3 or 8-11, respectively, and characterized by 1H and 31P{ 1H} NMR spectroscopy. Ligands 3, 8, 10 and 12 have been used to prepare in situ oligomerization catalysts by reaction with one equiv. of [Ni(COD)2] and PPh3 under an ethylene pressure of 30 or 60 bar. The catalyst prepared in situ from 12, [Ni(COD)2] and PPh 3 was the most active of the series with a TON of 12 700 mol C 2H4 (mol Ni)-1 under 30 bar ethylene. When the β-keto phosphorus ylide 8 was reacted in situ with three equiv. of [Ni(COD)2] and one equiv. of PPh3 under 30 bar of ethylene, ethylene polymerization was observed with a TON of 5500 mol C 2H4 (mol Ni)-1. The Royal Society of Chemistry.
- Kermagoret, Anthony,Braunstein, Pierre
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p. 822 - 831
(2008/09/20)
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- Catalytic applications of keto-stabilised phosphorus ylides based on a macrocyclic scaffold: Calixarenes with one or two pendant Ni(P,O)-subunits as ethylene oligomerisation and polymerisation catalysts
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Four calix[4]arenes containing either one or two ylidic -C(O)CHPPh 3 moieties anchored at p-phenolic carbon atoms were prepared starting from cone-25,27-dipropoxycalix[4]arene (1): 1,3-alternate-5,17-bis(2- triphenylphosphoranylideneacetyl)-25,
- Kuhn, Pierre,Semeril, David,Jeunesse, Catherine,Matt, Dominique,Lutz, Pierre J.,Louis, Remy,Neuburger, Markus
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p. 3647 - 3659
(2007/10/03)
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- Catalytic C-C coupling reactions at nickel by C-F activation of a pyrimidine in the presence of a C-Cl bond: The crucial role of highly reactive fluoro complexes
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Treatment of [Ni(COD)2] (COD = 1,5-cyclooctadiene) with 5-chloro-2,4,6-trifluoropyrimidine (1) in the presence of PiPr 3 or PPh3 effects the formation of the fluoro complexes trans-[NiF(4-C4N2ClF2)(PiPr 3)2] (3) and trans-[NiF(4-C4N 2ClF2)(PPh3)2] (4). The chloro complex trans-[NiCl(4-C4N2ClF2)(PPh 3)2] (5) can be prepared by reaction of 4 with Me 3SiCl. In contrast, a reaction of 1 with [Pd(PPh3) 4] leads to the insertion of a {Pd(PPh3)2} unit into the C-Cl bond yielding trans-[PdCl(5-C4N2F 3)(PPh3)2] (6). Treatment of 4 with an excess of TolB(OH)2 at 273 K results in the slow formation of trans-[NiF(4-C4N2TolClF)(PPh3)2] (7) and subsequently 5-chloro-2-fluoro-4,6-ditolylpyrimidine (8). Quenching of a solution of 7 with Me3SiCl leads to the chloro derivative trans-[NiCl(4-C4N2TolClF)(PPh3)2] (9). Treatment of 4 with PhB(OH)2 followed by addition of Me 3SiCl gives the complex trans-[NiCl(4-C4N 2PhClF)(PPh3)2] (10). In catalytic experiments, 1 is converted with the boronic acids TolB(OH)2, PhB(OH) 2, and p-F3CC6H4B(OH)2 into the 5-chloro-2-fluoro-4,6-diarylpyrimidines 8, 11, and 12 in 73%, 88%, and 37% yield, respectively, when 10% of 4 is employed as catalyst. The molecular structures of the complexes 5, 6, and 10 have been determined by X-ray crystallography. The studies reported in this paper represent the first catalytic C-C coupling reactions involving the activation of a C-F bond in the presence of a thermodynamically weaker C-Cl bond. They provide a route to access 5-chloro-2-fluoro-4,6-diarylpyrimidines, which have not been described before. There is considerable evidence that the presence of the fluoro ligand in 4 is crucial for the transmetalation step to occur and for the catalytic cycle to proceed.
- Steffen, Andreas,Sladek, Marianna I.,Braun, Thomas,Neumann, Beate,Stammler, Hans-Georg
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p. 4057 - 4064
(2008/10/09)
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- New open tetraaza nickel(II) and palladium(II) complexes. Different reactivity of the electrogenerated M(0) species toward difunctional substrates
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A series of neutral and cationic Ni(II) and Pd(II) complexes with the open tetraaza ligand bisoxazoline bisamine N4, were prepared and characterized. Neutral complexes presented dimeric structures of stoichiometry [M2(μ-N4)X4] (M = Ni (1), Pd (2)) and underwent slow decomplexation in coordinating solvents. Cationic monomeric [M(N4)]Y2 (M = Ni (3), Pd (4)) compounds were stable in solution and were efficient catalysts in electrochemical reactions involving difunctional substrates, unsaturated o-haloaryl and o-halobenzyl ethers. [Ni(N4)]2+-catalyzed reactions led to intramolecular cyclization products via initial oxidative addition on the C-X bond, whereas [Pd(N4)]2+-catalyzed processes involved the cleavage of the C-O bond. Furthermore, organometallic σ-Ni(II) (7a,b) and π-allylpalladium(II) (8a,b) complexes were prepared in order to study the intermediate species proposed in the catalytic cycles.
- Gómez, Montserrat,Muller, Guillermo,Panyella, David,Rocamora, Mercè,Du?ach, Elisabet,Olivero, Sandra,Clinet, Jean-Claude
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p. 5900 - 5908
(2008/10/08)
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- Stereoselective synthesis of allylic boronates via palladium-catalyzed cross-coupling reaction of Knochel's (dialkoxyboryl)methylzinc reagents with 1-halo-1-alkenes
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The cross-coupling reaction of (dialkoxyboryl)methylzinc regents IZnCH2B(OR)2 with 1-halo-1-alkenes was catalyzed by triphenylphosphine- or triphenylarsine-based palladium complexes to provide esters of stereodefined allylboronic acids with stereoselectiv
- Watanabe, Takeo,Miyaura, Norio,Suzuki, Akira
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- Nickel(0)-Catalyzed Dimerization of 1,2,3-Cycloheptatriene: Cyclobutadicycloheptatetraene, a Radialene Derivative
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Reaction of (7-bromotricyclo2,7>hept-1-yl)trimethylsilane (4) with cesium fluoride in dimethylformamide at room temperature in the presence of (Ph3P)4Ni afforded a 32percent yield of the radialene derivative 3.The formation of 3 is interpreted as a Ni(0)-catalyzed dimerization of the elusive 1,2,3-cycloheptatriene (2), which is generated by thermal rearrangement of the highly strained tricyclo2,7>hept-1(7)-ene (1).The X-ray structure of 3 shows an essentially planar radialene subunit. - Key Words: Radialene derivative / 1,2,3-Cycloheptatriene, dimerization / Cyclobutadicycloheptatetraene
- Hashmi, Stephen,Polborn, Kurt,Szeimies, Guenter
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p. 2399 - 2402
(2007/10/02)
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- NEW REACTIONS OF PYRIDINES AND TOTAL SYNTHESIS OF THE FUNGAL TOXIN ORELLANINE
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Dihalogenated pyridines react easily with sulphur nucleophiles, in dipolar aprotic solvents (DMF), to afford the products of mono- or of bis-substitution depending on the experimental conditions.On the contrary, with oxygen nucleophiles the bis-substituted products can be obtained only with some particular substrates.A new and efficient procedure to effect the homo-coupling of halogenoarenes will be presented.This reaction, wich occurs under the influence of low-valent nickel complexes, allowed us to effect the total synthesis of Orellanine, the lethal toxin of Cortinarius orellanus mushroom, as well as the syntheses of its decompositionproducts Orellinine and Orelline.The chemical properties of these three products and their behaviour towards UV irradiation will be presented and discussed.
- Tiecco, Marcello
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p. 1009 - 1020
(2007/10/02)
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- The synthesis and vibrational spectra of tetrakistrimethylphosphinenickel(0) and -platinum(0), Ni(PMe3)4 and Pt(PMe3)4
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The syntheses of the molecules Ni(PMe3)4 and Pt(PMe3)4 are reported for the first time.The platinum compound is much less stable than the nickel analogue.Raman and i.r. spectra have been obtained for the nickel compound and a complete vibrational assignment is proposed on the basis of Td molecular symmetry.For the platinum compound only the i.r. spectrum has been obtained.
- Edwards, H. G. M.
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p. 1401 - 1404
(2007/10/02)
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- Organonickel cyanide chemistry. Reactions of [(PhC≡CPh)Ni(CN)2]2-. An improved synthesis of [Ni(CN)2(CO)2]2-
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The reactions of (K·18-crown-6)2[(η2-PhC≡ CPh)Ni(CN)2] (1) with CO, P(OMe)3, alkynes, and α-bromo-p-xylene are described. Reaction of 1 with CO provides a route to a pure, stable salt of the Ni(CN)2(CO)22- anion. Compound 1 is a catalyst for the trimerization of terminal alkynes.
- Del Rosario, Renato,Stuhl, Louis S.
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p. 1260 - 1262
(2008/10/08)
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- TRANSITION METAL ALLYLS VI. THE STOICHIOMETRIC REACTION OF 1,3-DIENES WITH LIGAND MODIFIED ZEROVALENT-NICKEL SYSTEMS
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Butadiene and methylsubstituted 1,3-dienes react with zerovalent-nickel-ligand complexes in a stoichiometric manner to give octadiendylnickel-ligand complexes.The structure, rearrangement and reactions with CO and P-donor ligands of these species have been studied with the help of 1H and 13C NMR spectroscopy.The results provide an insight into the mechanism of the nickel-catalyesd cyclodimerization of 1,3-dienes.
- Benn, R.,Buessemeier, B.,Holle, S.,Jolly, P. W.,Mynott, R.,et all.
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- INTERACTION OF A ZEROVALENT NICKEL COMPLEX WITH ORGANOMERCURIALS
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The oxidative addition of ArHgX (Ar=Ph, X=Cl; Ar=C6F5, X=Br) to the nickel complex (Ph3P)4Ni resulting in formation of ?-aryl derivatives of bivalent nickel, (Ph3P)2Ni(Ar)X, has been performed.It was found that the reaction between (Ph3P)4Ni and (C6F5)2Hg yields the bimetallic compound (Ph3P)2Ni(C6F5)HgC6F5.Similarly, the reaction between 3Hg and (Ph3P)4Ni gives (Ph3P)2NiHgGe(C6F5)3, containing a Ge-Ni-Hg-Ge chain.A five-membered metallocycle with a N -> Ni chelate bond was obtained from the reaction of (Ph3P)4Ni with 8-(α-bromomercuriethyl)quinoline.
- Isaeva, L. S.,Morozova, L. N.,Bashilov, V. V.,Petrovskii, P. V.,Sokolov, V. I.,Reutov, O. A.
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p. 253 - 256
(2007/10/02)
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- Coupling of Organic Halides electrocatalyzed by the NiII/NiI/Ni0-PPh3 System. A Mechanistic Study based on an Electroanalytical Approach
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The coupling of the organic halides bromobenzene, 1-iodobutane, 1-iodo-2,2-dimethylpropane, and benzyl chloride has been carried out by electrochemically generating and continuously recycling the nickel(0) complex promoter .This species undergoes oxidative addition by organic halides leading to ?-bonded organometallic nickel(II) derivatives.In these complexes the metal-carbon bond can be cleaved either by a straightforward thermal decomposition or by a cathodic reduction, depending upon whether the co-ordinated organic group is an alkyl or an aryl one.In the former case a high yield of the coupling product is obtained only by employing organic halides not bearing hydrogen atoms in the β position; when a β-elimination reaction can occur, the yield of the coupling product is, on the contrary, very low and can be significantly improved only by carrying out the reductive process at more negative potentials, at which a proposed nickel hydride intermediate can be reduced.When the co-ordinated organic group is an aryl one, reductive elimination of the organic group does not occur by thermal decomposition and the coupling product can be formed only by means of a cathodic reduction of the relevant organometallic nickel(II) derivative.An overall mechanism is proposed which is consistent with the data.
- Schiavon, Gilberto,Bontempelli, Gino,Corain, Benedetto
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p. 1074 - 1081
(2007/10/02)
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- SUBSTITUTION NUCLEOPHILE VINYLIQUE PAR LE REACTIF DE REFORMATSKY CATALYSSE PAR DES COMPLEXES DU NICKEL ET DU PALLADIUM ZEROVALENTS. SYNTHESE D'ESTERS β,γ-ETHYLENIQUES
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Zerovalent complexes of palladium and nickel catalyse vinylic nucleophilic substitution by the Reformatsky reagent giving β,γ-ethylenic esters.Formation of a ?-vinylpalladium complex is the rate-determining step of the reaction.
- Fauvarque, J.F.,Jutand, A.
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p. 109 - 114
(2007/10/02)
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- Electroanalytical Investigation on Ligand-disproportionation and -exchange Equilibria in Nickel(II) and Nickel(I) Halide Phosphine Complexes in Acetonitrile
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Redox reactions of complexes (L = PPh3; X = Cl, Br, or I) at platinum electrodes in acetonitrile solution have been investigated by cyclic voltammetry, controlled-potential electrolysis, and spectrophotometry.The complexes undergo quantitative ligand disproportionation giving ionic species, and the nickel(I) complexes obtained as reduction products exhibit ligand-exchange equilibria.The nickel(0) species obtained in a further reduction process is not involved in any ligand-exchange reaction.The results demonstrate that the degree of reversibility of the redox processes depends markedly on the nature of the ligand set present in both the redox partners.The dependence of the reduction potentials on the nature of the halide ligands is discussed.
- Bontempelli, Gino,Magno, Franco,Nobili, Maria De,Schiavon, Gilberto
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p. 2288 - 2293
(2007/10/02)
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