Nickel, electrophilic addition with

It is generally assumed that the Lewis acid in 3 decreases the charge on the metal, i.e., increases its electrophilicity. The removal of charge from the nickel allows additional electron donors to coordinate to the nickel atom, and reaction with, for example, 2 moles of carbon monoxide or 1 mole of 1,5-cyclooctadiene (COD) gives the insoluble, catalytically inactive and presumably ionic complexes 7 and 8. In contrast, 7r-allyl-nickel halides (1) add only 1 mole of carbon monoxide while they do not react with COD (52). 

The synthesis of such eight-membered rings by the nickel-catalysed dimerisation of butadienes, is used here with 2-methylbutadiene. The regio-selectivity and stereo-specificity of the hydro-boration of symmetrical 124 are as expected for a trisubstituted alkene. Conversion of the alcohol 125 into a good leaving group 126 made it reactive enough to carry out electrophilic addition on the other alkene. In aqueous solution, the final nucleophile was water and the product a mixture of diastereoisomers of the tertiary alcohol 127. 

Perfluorodithiocin (187), in apparent accord with its formulation as a delocalized system, is unreactive toward electrophilic addition of bromine (Br2/CCl4) and toward oxidation (NalO MeOH) <7lTL287l>. This compound may be desulfurized with Raney nickel, affording tetrafluoro-cyclobutene and a second product, of unidentified structure, which appears to aris from further reduction of the anticipated bicyclobutenyl derivative. The latter is identical to the product formed by the treatment of authentic bicyclobutenyl with Raney nickel (Scheme 59) <7lTL287i>. 

By means of nickel-catalyzed couplings of vinyl zirconocenes, Schwaebe et al. succeeded in obtaining fluorinated materials using a-bromo esters as electrophiles (Scheme 4.62) [113]. The yields achieved, albeit modest (24—65%), were far better using Ni(0) than those obtained in experiments based on several palladium(O) sources (no product observed). Isopropyl esters appear to be crucial, as competing 1,2-addition occurs with both ethyl and n-butyl analogues. Curiously, t-butyl esters were found to completely inhibit both modes of reaction of the zirconocene. 

Transition metal complexes which react with diazoalkanes to yield carbene complexes can be catalysts for diazodecomposition (see Section 4.1). In addition to the requirements mentioned above (free coordination site, electrophi-licity), transition metal complexes can catalyze the decomposition of diazoalkanes if the corresponding carbene complexes are capable of transferring the carbene fragment to a substrate with simultaneous regeneration of the original complex. Metal carbonyls of chromium, iron, cobalt, nickel, molybdenum, and tungsten all catalyze the decomposition of diazomethane [493]. Other related catalysts are (CO)5W=C(OMe)Ph [509], [Cp(CO)2Fe(THF)][BF4] [510,511], and (CO)5Cr(COD) [52,512]. These compounds are sufficiently electrophilic to catalyze the decomposition of weakly nucleophilic, acceptor-substituted diazoalkanes. 

Functionalization of Ni(MeCOCHCOMe)2 occurs in reactions with isocyanates, diethyl azodi-carboxylate and dimethyl acetylenedicarboxylate, which proceed by formal insertion of the methine C—H unit into the substrate multiple bonds to form respectively amides and ester-substituted hydrazines and alkenes. Similar additions of acetylacetone to these electrophiles is catalyzed by nickel acetylacetonate.217,218... 

The nature of the additional nucleophile may be varied. For example, the reaction of the nickel(n) complex 6.56 with formaldehyde and methylamine gives the macrocyclic complex 6.57 (Fig. 6-46). Again, it is not clear whether the first steps of the reaction involve reaction with formaldehyde, followed by attack of amine upon the imine, or initial formation of an electrophile such as H2C=NMe, which attacks 6.56. 

Grignard additions, 9, 59, 9, 64 indium-mediated allylation, 9, 687 in nickel complexes, 8, 150 ruthenium carbonyl reactions, 7, 142 ruthenium half-sandwiches, 6, 478 and selenium electrophiles, 9, W11 4( > 2 in vanadocene reactions, 5, 39 Nitrites, with trinuclear Os clusters, 6, 733 Nitroalkenes, Grignard additions, 9, 59-60 Nitroarenes, and Grignard reactivity, 9, 70 Nitrobenzenes, reductive aminocarbonylation, 11, 543... 

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