Nickel anion transfer

With substances that give up an electron more readily than aromatic hydrocarbons, such as potassium, nickel carbonyl, cyanide ion, or iodide ion, complete transfer of an electron occurs and the TCNE anion radical is formed (11). Potassium iodide is a particulady usefiil reagent for this purpose, and merely dissolving potassium iodide in an acetonitrile solution of TCNE causes the potassium salt of the anion radical to precipitate as bronze-colored crystals. 

The phase-transfer catalysed reaction of nickel tetracarbonyl with sodium hydroxide under carbon monoxide produces the nickel carbonyl dianions, Ni,(CO) 2- and Ni6(CO)162, which convert allyl chloride into a mixture of but-3-enoic and but-2-enoic acids [18]. However, in view of the high toxicity of the volatile nickel tetracarbonyl, the use of the nickel cyanide as a precursor for the carbonyl complexes is preferred. Pretreatment of the cyanide with carbon monoxide under basic conditions is thought to produce the tricarbonylnickel cyanide anion [19], as the active metal catalyst. Reaction with allyl halides, in a manner analogous to that outlined for the preparation of the arylacetic acids, produces the butenoic acids (Table 8.7). 

Organoelement groups like the phenylthio- or diphenylarsanyl group can be removed reductively from alkyl residues very well by Raney-Nickel (Scheme 8). But the transfer of this splitting reaction to our products of anionic cycloadditions - pyrrolidine derivatives - led to difficulties because, as demonstrated in Scheme 8, in addition to the splitting of the element carbon bond ring opening or aromatization occured. 

The reductant is the deazaflavin F420 and the reactions parallel those for conversion of formyl-THF to methyl-THF (Fig. 15-18).431 440b 441 The methyl group of methyl-H4MPT is then transferred to the sulfur atom of the thiolate anion of coenzyme M, from which it is reduced off as CH4. This is a complex process requiring the nickel-containing F430,... 

Another series of oxygen transfer reactions involves neutral molecules such as N204, NO, C02 and S02, with formation of anionic species coordinated to nickel(II) (equations 70-73).27... 

The electrochemical hydrogenation of double bonds can be performed either electrocatalytically at Raney nickel, palladium, or platinum modified electrodes [32] or via electron transfer under Birch conditions to the intermediate anion radical [33]. Examples are given in the dihydrogenation of phthalic acid (Eq. 22.15) and the hydrogenation of heteroaromatic compounds (Eq. 22.14). 

Yang et al. used a similar protocol (an ether functionality supported on a primary alkyl halide carrier) to introduce an acetal on either side of the imidazole ring generating an ether functionalised ionic liquid (IL) imidazolium salt [183] (see Rguie 3.58). The anion could be varied without loss of the IL property (melting point below 1(X) °C) [184]. Synthesis of the transition metal carbene complexes (palladium) was done by carbene transfer ftom the corresponding silver(I) complexes or by reaction with the metal acetate (nickel) [162] (see Figure 3.64). 

We have also observed that the sensitivity of aryl-methyl-nickel compounds la and b to oxygen is greatly enhanced by the addition of methylllthium. Under these conditions, the presence of la and b as nickelate complexes in is indicated by isotopic excliange studies. These anionic nT el complexes should be even better donors than their neutral counterparts 1,(26) and they are thus expected also to show enhanced reactivity to aryl bromides in those interactions proceeding by electron transfer. Reductive eliminations similar to those presented for 1 can be formulated as ... 

In recent years. X-ray crystallography has led to the discovery of several novel metalloclusters of complex architecture that contain at least four metal ions (4, 5). They represent the active site of several redox enzymes that contain molybdenum, nickel, and manganese, as well as the most commonly encountered iron and copper (Fig. 6). These enzymes are extremely specialized in the oxidation or reduction reactions of the smallest molecules and anions (which include N2, CO, and H2). A common feature of such clusters is that they are present in enzymes as part of a more extensive electron transfer chain that involves a series of... 

Raney niekel can be used for the ehemoselective reduction of a,y9-unsaturated ketones, esters, acids, nitriles, and nitroalkenes to give the corresponding saturated carbonyl compounds and carbonyl analogs in excellent yields. From trapping experiments it became evident that electron transfer from nickel to give the enone radical anion initiates the reaction which then proceeds via proton transfer and second electron-proton transfer cycle (Scheme 8) [37]. 

A radical cation salt of tetraselenotetracene 7 with the anion [Fe(NO)(CN)5] was prepared and the crystal structure reported, which revealed the composition (7)3[Fe(NO)(CN)5] <2002MI520>. Charge-transfer salts of 7 and nickel(rv) bis((3)-l,2-dicarbollide) were also investigated by X-ray crystallography <19950M666>. The X-ray crystal structure of phenanthro[l,10-rz/ 8,9-r 4 ]bis-l,2-diselenole 8 has been reported <1995JMC1539>. 

The transfer of halide from 7r-allylnickel halide to aluminum to give a haloaluminum anion results in a strong decrease in the electron density and formation of free coordination positions on nickel. The presence and number of free coordination positions can be demonstrated by reaction with carbon monoxide. The catalytically active complex, XIII, reacts at —40°C. with 2 moles of carbon monoxide to give the inactive XIV which can be isolated. In XIII, there are accordingly two free coordination positions. During catalysis, these positions are presumably occupied by olefins in the form of 7r-complexes. A stable olefin 7r-complex, 7r-allylnickel (7T-cycloocta-l,5-diene) aluminum tetrabromide, XV, can actually be isolated by adding cycloocta-l,5-diene to a solution of the active complex, XIII. 

In contrast to the cobalt-based system, small amounts of H2 and no CO are produced when nickel cyclam or other saturated 14-membered tetraazamacrocycles (L) in Figure 3 are used to replace the cobalt complex in the above system [22]. Flash photolysis studies indicate that the electron-transfer rate constant (kn) for the reaction of the />-terphenyl radical anion with Nil (cyclam)2 is 4.3 x 10 M s. However, when CO2 is added to the solution, the decay of the TP anion becomes slower Flash photolysis studies of the acetonitrile solutions... 

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