1295-35-8Relevant articles and documents
Preparation of Ni(cod)2 Using Light as the Source of Energy
Ishida, Naoki,Kamae, Yoshiki,Murakami, Masahiro
, p. 1413 - 1416 (2019)
A convenient method to prepare Ni(cod)2 from Ni(acac)2 using light as the source of energy is reported. In the first step of this process, xanthone is reductively dimerized upon irradiation of solar or LED light in 2-propanol to form a vicinal diol possessing a highly sterically congested C-C bond. In the second step, a ketyl radical derived from the diol reacts with Ni(acac)2, ultimately reducing nickel(II) to nickel(0), which is bound by 1,5-cyclooctadiene (COD) to produce Ni(cod)2. This new method obviates the need for hazardous reductants such as diisobutylaluminum hydride (DIBAH) and sodium.
Zur Lewisaciditat von Nickel(0) VII. Alkalimetall-μ3-hydrido-tetrakis(ethen)diniccolat(0)-Komplexe: (pmdta)Li(μ3-H)Ni2(C2H4)4 und (pmdta)Na(μ3-H)Ni2(C2H4)4
Porschke, Klaus Richard,Wilke, Gunther
, p. 257 - 262 (1988)
Ni(C2H4)3 reacts with alkalimetal hydridoaluminates or -gallates MAHA1/GaR3 and MAH2AlR2 (R = alkyl) in ether/pmdta at temperatures between -70 and -20 oC to yield the ion pair complexes (pmdta)MA(μ3-
Hughes
, p. 4073 (1971)
Skell, P. S.,Havel, J. J.,Williams-Smith, D. L.,McGlichey, M. J.
, (1972)
The Anionic Pathway in the Nickel-Catalysed Cross-Coupling of Aryl Ethers
Borys, Andryj M.,Hevia, Eva
, p. 24659 - 24667 (2021)
The Ni-catalysed cross-coupling of aryl ethers is a powerful method to forge new C?C and C?heteroatom bonds. However, the inert C(sp2)?O bond means that a canonical mechanism that relies on the oxidative addition of the aryl ether to a Ni0 centre is thermodynamically and kinetically unfavourable, which suggests that alternative mechanisms may be involved. Here, we provide spectroscopic and structural insights into the anionic pathway, which relies on the formation of electron-rich hetero-bimetallic nickelates by adding organometallic nucleophiles to a Ni0 centre. Assessing the rich co-complexation chemistry between Ni(COD)2 and PhLi has led to the structures and solution-state chemistry of a diverse family of catalytically competent lithium nickelates being unveiled. In addition, we demonstrate dramatic solvent and donor effects, which suggest that the cooperative activation of the aryl ether substrate by Ni0-ate complexes plays a key role in the catalytic cycle.
Allylnickel(II) complexes of bulky 5-substituted-2-iminopyrrolyl ligands
Cruz, Tiago F. C.,Gomes, Pedro T.,Lopes, Patrícia S.
, (2021)
The optimized reaction between [Ni(COD)2] (COD = 1,5-cyclooctadiene) and ligand precursor 5-(2,4,6-triisopropylphenyl)-2-[N-(2,6-diisopropylphenyl)-formimino]-1H-pyrrole yielded the η3-cyclooctenyl-Ni(II) complex [Ni{κ2N,N’-5-(2,4,6-iPr3C6H2)-NC4H2-2-C(H) = N(2,6-iPr2C6H3)}(η3-C8H13)] 1. Subsequently, the η3-allyl complexes [Ni{κ2N,N’-5-R-NC4H2-2-C(H)=N(2,6-iPr2C6H3)}(η3-C3H5)] (R = 3,5-(CF3)2C6H3 (2a), 2,6-Me2C6H3 (2b), 2,4,6-iPr3C6H2 (2c) and CPh3 (2d)) were prepared in good yields via metathesis of [Ni(η3-C3H5)(μ-Br)]2 with the respective potassium 5-R-2-[N-(2,6-diisopropylphenyl)formimino]pyrrolyl salt (KLa-d). Complexes 1 and 2a-d were characterized by NMR spectroscopy, elemental analysis and complex 2d further analyzed by single crystal X-ray diffraction. Addition of excess pyridine to solutions of complexes 2a-d led to the observation of a fluxional process that, according to VT-NMR experiments, corresponds to a pyridine-assisted cis–trans isomerization process occurring in these complexes, via a η3-η1-η3 haptotropic shift of the allyl ligand, with ΔG? values in range of 9.5–17.3 kcal mol?1. Additionally, complexes 2a-d, when activated by B(C6F5)3, slowly catalyzed the isomerization of hex-1-ene to mixtures of internal olefins.
Diboron-Promoted Reduction of Ni(II) Salts: Precatalyst Activation Studies Relevant to Ni-Catalyzed Borylation Reactions
Joannou, Matthew V.,Sarjeant, Amy A.,Wisniewski, Steven R.
, p. 2691 - 2700 (2021/08/20)
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.
Role of the X Coligands in Cyclometalated [Ni(Phbpy)X] Complexes (HPhbpy = 6-Phenyl-2,2′-bipyridine)
Chin, Mason T.,H?rner, Gerald,Klein, Axel,Kletsch, Lukas,Sandleben, Aaron,Sch?fer, Sascha,Vicic, David A.,Vogt, Nicolas
supporting information, p. 1776 - 1785 (2021/06/28)
The coligand X was varied in the organonickel complexes [Ni(Phbpy)X] (X = F, Cl, Br, I, C6F5) carrying the anionic tridentate CNN ligand 6-(phen-2-ide)-2,2′-bipyridine (Phbpy-) to study its effect on electronic structures of these complexes and their activity in Negishi-like C-C cross-coupling catalysis. The complexes were synthesized from the precursor [Ni(COD)2] (COD = 1,5-cyclooctadiene) by chelate-assisted oxidative addition into the phenyl C-X bond of the protoligand 6-(2-halidophenyl)-2,2′-bipyridine) and were obtained as red powders. Protoligands X-Phbpy carrying the halide surrogates X = OMe, OTf (triflate) failed in this reaction. Single-crystal XRD allowed us to add the structures of [Ni(Phbpy)Cl] and [Ni(Phbpy)I] to the previously reported Br derivative. Cyclic voltammetry showed reversible reductions for X = C6F5, F, Cl, while for Br and I the reversibility is reduced through rapid splitting of X- after reduction (EC mechanism). UV-vis spectroelectrochemistry confirmed the decreasing degree of reversibility along the series C6F5 > F > Cl ? Br > I, which parallels the "leaving group character"of the X coligands. This method also revealed mainly bpy centered reduction and essentially Ni(II)/Ni(III) oxidations, as corroborated by DFT calculations. The rather X-invariant long-wavelength UV-vis absorptions and excited states were analyzed in detail using TD-DFT and were consistent with predominant metal to ligand charge transfer (MLCT) character. Initial catalytic tests under Negishi-like conditions showed the complexes to be active as catalysts in C-C cross-coupling reactions but did not display marked differences along the series from Ni-F to Ni-I.
