Nickel Acac

Naphlhyl)ethylisocyanaie 301 Nickel 45, 116,356,374 Nickel Acac 339 Nickel cyanide 316 Nnkel peroxide 213... 

However, with the application in the 19, iOs of crystal held theory to transition-metal ehemistry it was realized that CFSEs were unfavourable to the lormation of tetrahedral d complexes, and previous assignments were re-examined. A typical ca.se was Ni(acac)i. which had often been cited as an example of a tetrahedral nickel complex, but which was shown - in I9. I6 to be trimeric and octahedral. The over-zealous were then inclined to regard tetrahedral d" as non-existent until Hrst L.. M. Venanz.i and then N., S. Gill and R. S. Nyholm" demonstrated the existence of discrete tetrahedral species which in some cases were also rather easily prepared. 

Figure 27.6 Some typical planar complexes of nickel (11) (a) Ni(Mcft-acac)2). (b) Ni(Me-sal)2] and (c) [Ni(dmgll)2. (Note the short 0-0 distance which is due to strong hydrogen bonding.)...

Monomer-oligomer equilibria. [Ni(Me-sal)2], mentioned above as a typical planar complex, is a much studied compound. In pyridine it is converted to the octahedral bispyridine adduct (/zsoo = 3.1 BM), while in chloroform or benzene the value of is intermediate but increases with concentration. This is ascribed to an equilibrium between the diamagnetic monomer and a paramagnetic dimer, which must involve a coordination number of the nickel of at least 5 a similar explanation is acceptable also for the paramagnetism of the solid when heated above 180°C. The trimerization of Ni(acac)2 to attain octahedral coordination has already been referred to but it may also be noted that it is reported to be monomeric and planar in dilute chloroform solutions. 

The reaction of 3-amino-4-cyanofurazan with (3-dicarbonyl compounds in the presence of catalytic amounts of nickel acetylacetonate (Ni(acac)2) gave labile enamines that on treatment with acetic acid afforded fused pyridines of type 100 in 80-95% total yields (Scheme 51) (94MC57). Eurther syntheses of furazano-pyridines can be found in the review by Sheremetev (99RCR137, 99UK154). 

Dimethylindene derivatives were hydroaluminated with BujAlH using Ni(acac)2 as the nickel(O) precursor (Scheme 2-13) [9]. Hydroalumination of the trisubstituted double bond in 9 was also achieved, although more forcing conditions... 

Nickel catalysts can be used instead of copper catalysts to promote the conjugate addition reaction, providing, in some cases, better results than the corresponding copper catalysts. In 2000, Yang et al. discovered a series of (li ,25, 3i )-3-mercaptocamphan-2-ol derivatives, which proved to be efficient ligands in the conjugate addition of ZnEt2 to chalcone upon catalysis with Ni(acac)2 (Scheme 2.29). 

Nickel acetylacetonate, Ni(acac)2, in the presence of a styrene derivative promotes coupling of primary alkyl iodides with organozinc reagents. The added styrene serves to stabilize the active catalytic species, and of the derivatives examined, m-trifluoromethylstyrene was the best.274... 

Bora-2,5-cyclohexadienes have a much greater synthetic potential than is apparent from the examples given so far. This may be exemplified by two recent reactions. Reductive complex formation in the system Co(acac)3/COD/25/Mg/THF affords complex 51 via the organotin route (77) while an earlier synthesis used the cobaltocene route (60). Ni(COD)2 very cleanly forms the (Tj3-l,4,5-cyclooctenyl)nickel complex 52 (29). 

Nickel(II) acetylaeetonate has been recommended as a very efficient homogeneous catalyst for intramolecular cyclopropanations for unsaturated diazoketones 171 The yields were better than with activated CuO as catalyst (see Table 10 for examples). The authors of this study seem to combine routinely thermocatalytic with photochemical (tungsten lamp) decomposition of the diazoketones. The benefit of this procedure (higher yields, shorter reaction times) has been communicated in the CuO case, but not for the Ni(acac)2-eatalyzed reaction. 

A unique nickel-catalyzed alkylative monofunctionalization of cyclic anhydrides using dialkylzinc and diphenylzinc provided 7- or f3-keto acids (Scheme 124).323 This reaction also required the use of Ni(cod)2 or Ni(acac)2 and a bidentate ligand. As it was observed by Knochel in the reactions of dialkylzinc with alkyl iodides (vide infra), addition of an electron-deficient alkene,324 for example, 4-fluoromethylstyrene, accelerated the rate of the reaction and increased the yield of the desired products. The alkylzinc reagents BuZnBr and Et02CCH2CH2ZnBr also reacted with anhydrides, although the yields were lower. 

The activity of Ziegler-type systems such as M(acac) -AlEt3 (M = Cr, Mn, Fe, Co, or Ni acac = acetylacetonate) was examined with 1-olefins and triethyl- or triethoxysilanes (55). Systems with nickel or cobalt showed low activity for hydrosilation but isomerized the olefin and were reduced to the metal. The study was extended to dienes and acetylenes (56). Isoprene gave the same products with these catalysts as are made with chloroplatinic acid. Penta-1,3-diene with Pt gave l-methylbut-2-en-ylsilanes. The Ziegler catalysts gave mainly penta-2-enylsilanes... 

Nickel(ll) acetylacetonate catalyzes the addition of acetylacetone or ethyl acetoacetate to carbodiimides (Equation (89)).447 The acetylacetonate ligand of Ni(acac)2 may react with a carbodiimide to give a nickel complex having a 3-substituted acetylacetonate, which is then protonated by another acetylacetone to afford an adduct and Ni(acac)2. 

It is postulated that the mechanism of the silane-mediated reaction involves silane oxidative addition to nickel(O) followed by diene hydrometallation to afford the nickel -jr-allyl complex A-16. Insertion of the appendant aldehyde provides the nickel alkoxide B-12, which upon oxygen-silicon reductive elimination affords the silyl protected product 71c along with nickel(O). Silane oxidative addition to nickel(O) closes the catalytic cycle. In contrast, the Bu 2Al(acac)-mediated reaction is believed to involve a pathway initiated by oxidative coupling of the diene and... 

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