Nickel complexes oxidation with

The benzoylhydrazone of benzaldehyde (57) is oxidatively cyclized at the nickel hydroxide electrode (0.1 M NaOH, 30% t-butanol 70 % water) to the oxadiazole 58, however in only moderate yield (22%). Main product is benzoic acid (59) (60%) additionally a nickel complex (14%) with the probable structure 60 is found (Eq. (17)) . With nickel peroxide in chloroform 30% 58 and 47% 60 are obtained... 

The alkyne complex, (77s—C5H5X775—C5Me5)Ti(diphenylacetylene) reacted with C02 to give a five-membered metallacycle.53 Similarly, nickel complexes reacted with alkynes and C02 to yield the same type of metallacycles.54 The oxidative coupling of C02 with imines (Schiff bases) at electron-rich nickel(O) centers leads to cyclic carbamato complexes.55... 

As described before, nickel complexes react with aldehydes stoichiometri-cally. In view of the fact that aldehydes may undergo oxidative addition to palladium complexes, it is rather peculiar that ketones are not formed via oxidative addition. (This reaction will be discussed again in Chapt. V.)... 

Lin BL, Clough CR, Hillhouse GL (2002) Interactions of aziridines with nickel complexes oxidative-addition and reductive-ehmination reactions that break and make C—N bonds. J Am Chem Soc 124 2890-2891... 

Monodentate dipolarophiles such as acrolein, methacrolein, and a-bromoacrolein could be successfully utilized in the l ,J -DBFOX/Ph-transition metal complex-catalyzed asymmetric nitrone cycloadditions [76]. The reactions of N-benzylideneani-line N-oxide with acrolein in the presence of the nickel(II) aqua complex R,R-DBF0X/Ph-Ni(C104)2 3H20 (10mol%) and MS 4 A produced a mixture of two regioisomers (5-formyl/4-formyl regioisomers ca 3 1). However, enantio-... 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

The interaction of NO, N20, and N02 reactants with the secondary copper-oxo sites leads to terminal 02, restoring the initial active sites (Figure 2.26). The central N02 semi-product is produced through oxidation of NO on the 3CuO Z centers, similarly to the nickel complexes described in Section 6.2.1. 

By oxidative addition of aryl sulphides to low-valent nickel complexes, a C—S bond cleavage occurs to form Ni11 thiolate complexes. For example, exposure of diaryl sulphides to [(But3P)3Ni0] leads to oxidative addition, with nickel inserting into the C—S bond (280).814... 

Also, the structure of the Ni11 complex (379) with the related ligand dimethyltetrathiomalonate has been determined.997 The geometry at the nickel center is approximately square planar with an inversion center. (379) shows reversible redox properties 998 Oxidation with I2 affords 1,3-bis (methylthio)-1,2-dithiolium triiodide. 

Low-valent nickel complexes of bpy are also efficient electrocatalysts in the reductive coupling reaction of aromatic halides.207 Detailed investigations are in agreement with a reaction mechanism involving the oxidative addition (Equation (40)) of the organic halide to a zero valent complex.208-210 Starting from [Nin(bpy)2(X)2]0 with excess bpy, or from [Nin(bpy)3]2 +, results in the [Ni°(bpy)2]° complex (Equations (37) and (38)). However, the reactive complex is the... 

It must be acknowledged, however, that the determination of the number of the different surface species which are formed during an adsorption process is often more difficult by means of calorimetry than by spectroscopic techniques. This may be phrased differently by saying that the resolution of spectra is usually better than the resolution of thermograms. Progress in data correction and analysis should probably improve the calorimetric results in that respect. The complex interactions with surface cations, anions, and defects which occur when carbon monoxide contacts nickel oxide at room temperature are thus revealed by the modifications of the infrared spectrum of the sample (75) but not by the differential heats of the CO-adsorption (76). Any modification of the nickel-oxide surface which alters its defect structure produces, however, a change of its energy spectrum with respect to carbon monoxide that is more clearly shown by heat-flow calorimetry (77) than by IR spectroscopy. 

Nickel halides and nickel complexes resulting from oxidative addition can also give rise to subsequent replacement and insertion reactions. Replacement reactions have been described mainly with arylnickel halide complexes (examples 23, 29, and 31, Table III). Carbanionic species replace halide ions and can undergo coupling or insertion reactions. An example of application of a carbanionic reaction to the synthesis of a natural product is the coupling step between an aromatic iodo-derivative and an active methylene group to form cephalotaxinone (example 23, Table III). 

Oxidation of organic substrates with molecular oxygen on nickel complexes is limited to a few known examples. 

Oxidation of carbon ligands with concomitant insertion has been observed in the reaction of methallyl nickel complexes with norbornene or strained olefins in general and oxygen (example 3, Table IX). 

Oxidative addition of the silyl species to nickel is followed by insertion of unsaturated substrates. Zero-valent nickel complexes, and complexes prepared by reducing nickel acetylacetonate with aluminum trialkyls or ethoxydialkyls, and in general Ziegler-Natta-type systems, are effective as catalysts (244, 260-262). Ni(CO)4 is specific for terminal attack of SiHCl3 on styrene (261). 

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