Nickel Ni complex

In 1977, Fahey and Mahan described the first C-F oxidative addition of hexafluo-robenzene (C ) to the zerovalent nickel complex [Ni(cod)(PEt3)j] [11], The reaction was very slow and led, after several days at 30-35°C, to the formation of trani-[Ni(CgF3)(F)(PEt3)2] in very poor yield (7%). The use of [NiCPEtj) ] for the same reaction by Perutz and co-workers 20 years later allowed for a better conversion but the reaction rate remained slow (4 weeks were necessary to obtain 48% of the desired product) [12],... 

Alternatively, CO2 can be used as source of CO. Indeed, it is well known that low-valent transition metal complexes can catalyze the chemical or electrochemical reduction of CO2 into CO. This approach was used to generate the mixed nickel complex Ni°bpy(CO)2 by the electrochemical reduction of Nibpy in NMP or DMF in the presence of CO2. The reduced complex can react with alkyl, benzyl, and allylhalides to give the symmetrical ketone along with the regeneration of Nibpy ". A two-step method alternating electroreduction and chemical coupling leading to the ketone has thus been set up (Scheme 9) [126,127]. 

The competing processes were sufficiently slower than the reaction of interest only in the case of the nickel complex, [Ni(NiL2)2]Cl2. Attempts to determine the rate of reaction of [Pd(NiL2)2]Cl2 with benzyl bromide revealed a very slow process occurring at a rate comparable to, but slightly slower than, the solvolysis of benzyl bromide. It is concluded that the rate of reaction of this complex with benzyl bromide is too slow for accurate rate study in methanol. 

In one instance, however, clear evidence has been obtained to suggest the formation of a peroxynitrate intermediate. Thus, the nickel complex Ni(NO)CI(diphos) reacts with 02 either in dimethylformamide or on irradiation in dichloromethane to form the nitro complex Ni(N02)Cl(di-phos). Evidence for the formation of a d9 nickel(I) intermediate came from ESR studies. This intermediate was considered to be the peroxy-bridge species (4) and the reaction sequence was believed to follow the sequence shown in Scheme 1. 

A crystal structure determination of [Pd(dtb)2] showed a distorted tetragonal arrangement of sulfur atoms about the palladium atom. The Pd—S distances in the square plane are 2.32-2.34 A, while the Pd—S (apical) distance is 3.46 A, suggesting some interaction. 47 The nickel complex [Ni(dtb)2] can be readily oxidized to [Ni dtbhSj], which was postulated to be a NiIV complex,136 but it is more likely that the complex contains Ni11 with the structure (42).146... 

The nickel complex, [Ni(NO)I], can also be prepared by the procedures outlined above. The compound is formed readily in reasonable yields, but it is significantly less stable than the iron and cobalt compounds. Moreover, although some of it can be sublimed, it decomposes slowly even below its sublimation temperature. The gram quantities used are the same as for cobalt, and no modification of the procedure is necessary until the sublimation step. No sublimation of the nickel complex takes place until the bath temperature reaches 155-165°C. At this temperature a small amount (2.5 g.) of product sublimes onto the cold probe. Anal. Calcd. for Ni(NO)I Ni, 27.22 I, 58.86. Found Ni, 26.8 I, 56.5. 

The assembly of 4-ferf-butylbenzoic acid and cyclam (A, Figure 2) [54] has a planar arrangement of the macrocycle s N4 donor set with a tram disposition of the carboxylates very similar to that observed in the structure of the nickel complex, [Ni(cyclam)(benzoate)2], (B, Figure 2).[55] Formation of the nickel complex from the assembly and extraction of the nickel ion can then be represented by the pH-swing equilibrium... 

The condensation of o-aminobenzamide and pyridine-2-carbaldehyde produced the terdentate ligand (129) which partially isomerizes in methanol, in the presence of nickel(n) nitrate, to form the cyclic ligand (130). The nickel complex [Ni( 129)(130)-(H20)](N03)2,4H20 has been X-rayed, and the results show that (129) bonds as a terdentate N20 donor, and (130) as a bidentate N2 ligand, the co-ordinated water molecule completing the irregular octahedron about the nickel.575... 

The catalytic cycle proposed for the dimerization of butadiene is shown in Fig. 7.8. As shown by 7.24, two molecules of butadiene coordinate to NiL. A formal oxidative addition, as shown by Eq. 7.8, produces two nickel-carbon bonds and the carbon-carbon bond required for ring formation. The structure of 7.25 with two nickel-carbon bonds (see Fig. 7.8), is a hypothetical one that helps us to understand the carbon-carbon bond formation process. The actual catalytic intermediates that have been observed by spectroscopy have an rf-allyl type of bonding. As shown by reaction 7.9, species 7.25 can reductively eliminate 1,5-cyclooctadiene and the zerovalent nickel complex Ni-L. 

Of the otherwise so stable hexammine nickel complexes [Ni(NH3)6]X2 the fluoride decomposes again immediately when one attempts to prepare it from the chloride by double decomposition with AgF. 

Vinyl sulfides have been prepared by the catalytic addition of the S—H bond of thiols (85) to terminal alkynes (86) under solvent-free conditions using the nickel complex Ni(acac)2 (47). High alkyne conversions (up to 99%) were achieved after 30 min at 40 °C in favor of the corresponding Markovnikov products (87) (equation 23). Other metal acetylacetonate complexes were examined for this reaction, but none showed any improvement over the nickel catalyst. Mechanistic details suggest that alkyne insertion into the Ni—S bond is important to the catalytic cycle and that nanosized structural units comprised of [Ni(SAr)2] represent the active form of the catalyst. Isothiocyanates and vinyl sulfides have been produced in related Rh(acac)(H2C=CH2)2 (6) and VO(acac)2 (35) catalyzed sulfenylation reactions of aryl cyanides and aryl acetylenes, respectively. 

The nickel complex, Ni ( 5115)2, has been made by the action of the Grignard reagent on nickel (II) acetylacetonate (217) or from potassium cyclopentadienyl and the ammine [Ni(NHs)el (S N)2 in liquid ammonia (58). It forms dark emerald-green crystals which sublime at 80-90° and which, when heated in nitrogen, melt, with decomposition and the formation of a nickel mirror, at 173-174°. It is only slowly oxidized in air, and cold water neither attacks nor dissolves it it is, however, readily soluble in organic liquids. Oxidation of the compound yields an orange-yellow solution containing the ion [Ni( 5H5)2]+, which is stable for a short period in weakly acidic media, and which may be precipitated as the reineckate or tetraphenylborate. 

A phosphine-based nickel(II) bromide complex (Ni-2) also induces living radical polymerization of MMA specifically when coupled with a bromide initiator in the presence of Al(0-i-Pr)3 as an additive in toluene at 60 and 80 °C.133 The reaction rates and the effects of radical inhibitors are similar to those with Ni-1, whereas chloride initiators are not effective in reaction control. Additives are not necessary when the polymerization is carried out in the bulk or at high concentrations of monomer, either methacrylate or /v-butyl acrylate (nBA).134 An alkylphosphine complex (Ni-3) is thermally more stable and can be employed for MMA, MA, and nBA in a wide range of temperatures (60—120 °C) without additives.135 A fast polymerization proceeds at 120 °C to reach 90% conversion in 2.5 h. A zerovalent nickel complex (Ni-4) is another class of catalyst for living radical polymerization of MMA in conjunction with a bromide initiator and Al(0-i-Pr)3 to afford polymers with narrow MWDs MJMn = 1.2—1.4) and controlled molecular weights.136 The Ni(0) activity is similar to that of Ni(II) complexes whereas the controllability... 

Structure-reactivity relationships in the cyclo-oligomerization of 1,3-butadiene catalyzed by zerovalent nickel complexes (Ni-heterocycles as intermediates) 03MI76. 

Typical examples of the stabilizers generally used to prevent the above chain reaction are (a) UV absorbers — 2(2-hydroxy-3-tert-butyl-5-methylpheny l)-5-c hi or ob en zo tr ia zo le and 2-h yd ro xy-4-octoxybenzophenone (b) Antioxidants — 3,5-di-tert-butyl-4-hydroxy-toluene and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propa-noate (c) Peroxide decomposers — dilauryl thiodipropionate. In addition quenchers such as the organic nickel complex, Ni(II) bis-(diisopropyl dithiocarbamate) are used for the deactivation of the excited states of the chromophoric groups responsible for light initiation. 

Rabinovich and coworkers44 reported an alternative preparation (Fig. 5.10) of the bulky TmBu together with convenient syntheses of [MBr(TniBu)] (M = Zn, Cd, Hg), structurally characterized. The isostructural complexes display a distorted tetrahedral structure, with the heavier members of the group exhibiting larger Br-M-S and smaller S-M-S angles. The nickel complexes [Ni(dppe)(Tm Bu)]X (X = Cl, Br) have been also described.6... 

The nitrogen molecule is readily displaced from solutions of the complex by argon to give the co-ordinatively unsaturated bis-(tricyclohexylphosphine)nickel complex, Ni[P(C6H11)3]2 in solution. This complex readily undergoes a variety of co-ordinative-addition and co-ordinative-oxidation reactions.2,5... 

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