Acetylacetone complexes with nickel

Catalytic homogeneous hydrogenation of cyclohexene has been claimed for simple systems such as nickel(II) acetylacetonate [39] or a nickel-chloride complex with two monodentate amines [40]. The latter complex was used as comparison for a heterogeneous catalyst obtained by impregnation of the complex on y-alu-mina [40]. SCRs of 100 were used at 30 atm. H2 and temperatures up to 100°C, resulting in conversions of only 20-35% after 1 h. 

The monomers dealt with can be polymerized by various mechanisms, not only by ROMP. For example, a rapid polymerization of norbornadiene occurs using a homogeneous catalytic system consisting of nickel acetylacetonate or a nickel-phosphine complex, such as nickel bis-(tri-n-butylphosphine) dichloride (NiCl2(TBP)2) or nickel bis-(tricyclohexylphosphine) dichloride (NiCl2(TBP)2). Nickel acetylacetonate as catalyst is known to initiate rather a classical vinyl polymerization (7). The classical vinyl polymerization... 

The archetype of -diketones is acetylacetone (2,4-pentanedione Scheme 21 R = R = Me R" = H). Nickel complexes with this ligand are very numerous and are the ones studied in most detail. 

Metal complexes with fluoro-/3-diketones have been comprehensively reviewed.1585 The introduction of electron-withdrawing groups in the chelate ring increases the Lewis acidity strength of the ML2 complexes, and consequently the bis adducts of the fluoro-/3-diketonato complexes are more stable than the corresponding complexes with /3-diketones. As an example of a nickel complex with 1,1,1-trifluoroacetylacetone which does not have a counterpart in the nickel acetylacetonate complexes we can mention the hexanuclear complex Ni6Lio(OH)2(H20)2.1586... 

Among the electrochemical syntheses related to the change of metal oxidation number, we emphasize obtaining acetylacetonates of divalent iron, cobalt, and nickel [551,623]. The method of alternating-current electrochemical synthesis was applied to isolate Ji-complexes of monovalent copper with allylamines, allylimines, and ally-lurea from the salts of divalent copper [624-628], We note that the same method was used for preparation of analogous ji-complexes with copper(II) halides (X = Cl, Br) [629a]. Other electrochemical syntheses with participation of metal salts and complexes are described in monographs [201,202] and literature cited therein. 

An alternative procedure starts from a metal complex of o-phenylenedi-amine. For example, the bis(o-phenylenediamine) complex of nickel(II) chloride reacts with acetylacetone to give a mixture of a nickel complex of the diamine and diketone together with 2,4-dimethylbenzodiazepinium chloride (76CPB1934 91JPR327). Chromium complexes have been used in the same way [91JCS(D)2045]. 

Two isomeric 1,5,9-cyclododecatrienes, namely, trans,trans,cis-CijH 18 (XLVI) and trans,trans,trans-CuHis (XLVII), are formed in good yield by the cyclic trimerization of butadiene using certain Ziegler-type catalysts 247, 250, 251, 252). The formation of these 12-membered ring hydrocarbons probably proceeds via metal 7r-complexed intermediates. When the cyclic triene (XLVII) is treated with nickel acetylacetonate and... 

Since the oxygen atoms as well as the alpha carbon on the /3-keto-enolate ring can function as bases to coordinate with metal ions (5, or to hydrogen bonding solvents (14)f it should be recognized that /3-keto-enolate complexes may have a stereochemistry quite different from that expected—based on the stoichiometry of the complex. However, by a suitable choice of a /3-ketoenol ligand, such as 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane), H-DPM, intermolecular effects can be reduced or eliminated with the result that the metal complex formed has the stereochemistry expected for the monomeric acetylacetonate complex of that metal ion. For example, nickel(II) acetylacetonate is trimeric as a solid and in solution (11), but the dipivaloylmethane complex is a monomeric, undoubtedly planar species, in solution, as well as in the solid state (37), This stereochemistry occurs with the monomeric acetylacetonate in dilute solution or in the vapor phase, as indicated by absorption spectra and electron diffraction (SO). 

The asymmetric conjugate addition of diethylzinc with chalcone was also catalyzed by nickel and cobalt complex (Eq. (12.31)) [71]. A catalytic process was achieved by using a combination of 17 mol% of an aminoalcohol 34 and nickel acetylacetonate in the reaction of diethylzinc and chalcone to provide the product in 90% ee [72, 73]. Proline-derived chiral diamine 35 was also effective, giving 82% ee [74]. Camphor-derived tridentate aminoalcohol 36 also catalyzes the conjugate addition reaction of diethylzinc in the presence of nickel acetylacetonate to afford the product in 83% ee [75]. Similarly, the ligand 37-cobalt acetylacetonate complex catalyzes the reaction to afford the product in 83% ee [76]. 

Synthetically more useful is the reaction of silylated alkynes with methyhnagne-sium bromide catalyzed by 10 mol% of the 1 1 complex of nickel acetylacetonate and trimethylaluminum in this reaction the regioselectivity is imposed by the bulky trimethylsilyl group (Scheme 3.74) [53]. 

Perfluormated oligoethers with the acetylacetonate group at the end of the polymer formed complexes 56 with nickel(I), which catalyzed ethylene oligomerization. The turnover number in the reaction reached 2460 in a perfluorinated ether-toluene two-phase system, and the catalyst, which was in the fluorine-containing phase, was readily separable [169]. 

Several independent determinations of the sign of the a-fluorine coupling constant have been made. The contact chemical shifts of the fluorine atoms of paramagnetic bis(fluoro-phenylaminotroponiminato)nickel(ll) complexes and of the nickel acetylacetonate complexes of O, m. and p-fluoroaniline as well as observations of chemically induced dynamic nuclear polarization in products obtained from fluorinated benzyl radicals are all in accord with the assignment of a positive sign, (o) D. R. Eaton, A. D. Josey, and W. A. Sheppard, J. Amer. Chem. Soc., 85, 2689 (1963). (b) M. R. Wasielewski, Thesis University of Chicago Library... 

By hydrolysis of the nickel-allyl-carboxylato complexes with mineral acids usually 3-pentene-carboxylic acids are formed [40]. Instead of mineral acids also acetylacetone can be used as displacing agent [44]. 

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