Ketone nickel -halide complex

Rieke and coworkers have found that a special type of activated metallic nickel, available through reduction of nickel(II) iodide with lithium metal, suffers oxidative addition of benzylic and allylic halides. The resulting nickel(Il) complexes readily undergo cross-coupling with acid chlorides to form ketones. Once again it was difficult to obtain, y-unsaturated ketones from this method. Moderate to good yields of simple ketones may be prepared by this method. 

Nickel-catalyzed ketone and aldehyde hydrosilylations have been developed with well-defined Ni(II) hydrides using phosphine anilide ligands (Scheme 3-84). This process is tolerant of a variety of functional groups including aryl halides. In mechanistically distinct processes, nickel(O) complexes of NHCs were shown to catalyze ketone hydrosilylations using carbohydrate-derived silanes in a process that allows reductive glycosylations of ketones. Chemoselectivity of the latter method was optimal in the presence of Ti(OR)4 additives. 

Nickel carbonyl, however, does not react with acids to form such complexes. Nevertheless, it is possible that a reaction similar to (2) could occur with an intermediate alkyne-nickel carbonyl complex, giving rise to the formation of an alkenylnickel dicarbonyl halide, RCH=CH—Ni(CO)2X, which could then yield the unsaturated acid according to Eq. (3a) or (3b) 12). This reaction formally would resemble the carbonylation of allyl halides, discussed in Section II, C. Divinyl ketones may be formed as by-products of carbonylation 13), and the stereochemistry of addition to the acetylenic linkage is reported to be exclusively cis 13). 

The reaction may be reasonably explained by the smooth oxidative addition of benzylic and acyl halides to nickel to afford benzylnickel halides and acylnickel halides. The metathesis of these complexes could give the acylbenzylnickel complex, which upon reductive elimination would yield the benzyl ketone. 

An intermediate acylnickel halide is first formed by oxidative addition of acyl halides to zero-valent nickel. This intermediate can attack unsaturated ligands with subsequent proton attack from water. It can give rise to benzyl- or benzoin-type coupling products, partially decarbonylate to give ketones, or react with organic halides to give ketones as well. Protonation of certain complexes can give aldehydes. Nickel chloride also acts as catalyst for Friedel-Crafts-type reactions. 

Catalytic processes based on the use of electrogenerated nickel(O) bipyridine complexes have been a prominent theme in the laboratories of Nedelec, Perichon, and Troupel some of the more recent work has involved the following (1) cross-coupling of aryl halides with ethyl chloroacetate [143], with activated olefins [144], and with activated alkyl halides [145], (2) coupling of organic halides with carbon monoxide to form ketones [146], (3) coupling of a-chloroketones with aryl halides to give O -arylated ketones [147], and (4) formation of ketones via reduction of a mixture of a benzyl or alkyl halide with a metal carbonyl [148]. 

Carbonylation of halides with tetramethyltin This nickel complex is the most efficient catalyst for the synthesis of methyl ketones by reaction of aryl halides with carbon monoxide and tetramethyltin in HMPT at 120°. No reaction occurs when tetraphenyltin is used. A typical reaction is formulated in equation (I). 

Electrogenerated nickel(O) bipyridine complexes serve as catalysts for a number of syntheses (a) formation of ketones from acyl halides and either alkyl or aryl halides [319], (b) production of, )/-unsaturated esters via coupling of a -haloesters with aryl or vinyl halides [320], (c) coupling of a-chloroesters or a-chloronitriles with carbonyl... 

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