Dialkyl nickel complexes, reaction

Reactions of organomagnesium compounds with dialkyl sulfates or alkyl sulfonates often give satisfactory yields of the products of displacement of sulfate or sulfonate. Side-reactions have been observed, but they can often be avoided for example, an excess of the sulfate or sulfonate should be used with Grignard reagents, as some is consumed by nucleophilic attack by halide ion [A]. The dialkyl sulfates are reactive, but hazardous. Toluenesulfonates (tosylates) are less reactive, but their reactions are catalysed by copper complexes the reactions of trifluoromethanesulfonates (triflates) are catalysed by nickel complexes. Reactions of Grignard reagents with secondary tosylates appear to follow an Sn2 mechanism, with inversion of configuration [43],... 

Steric constraints dictate that reactions of organohalides catalysed by square planar nickel complexes cannot involve a cw-dialkyl or diaryl Ni(iii) intermediate. The mechanistic aspects of these reactions have been studied using a macrocyclic tetraaza-ligand [209] while quantitative studies on primary alkyl halides used Ni(n)(salen) as catalyst source [210]. One-electron reduction affords Ni(l)(salen) which is involved in the catalytic cycle. Nickel(l) interacts with alkyl halides by an outer sphere single electron transfer process to give alkyl radicals and Ni(ii). The radicals take part in bimolecular reactions of dimerization and disproportionation, react with added species or react with Ni(t) to form the alkylnickel(n)(salen). Alkanes are also fonned by protolysis of the alkylNi(ii). 

Similarly, copper salts (cupric and cuprous) facilitate the reaction of aryl halides with trialkyl phosphites in the formation of dialkyl arylphosphonates under conditions like those found in nickel systems.37-39 Again, the copper salts appear to undergo an initial reaction with the phosphites to form a complex that subsequently undergoes reaction with the aryl halide. The requirement for copper is also similar to that for nickel saltstonly a catalytic amount is needed. Further, a preference among halides on the aromatic ring is noted iodide is replaced preferentially to other halides (Figure 6.10).40... 

Addition of triphenylphosphine or t-butylisocyanide to 101 affords the analogous five-coordinate complexes 102b and 102c. These species represent rare examples of stable five-coordinate ds-dialkyl complexes of Ni(II), although stable trigonal-bipyramidal trans-dialkyls of nickel are well known (176-178), and they provide a structural model for a putative square-pyramidal intermediate in reductive elimination reactions of ds-dialkyl... 

Sometimes this deactivation is so great that co-ordinated amines are non-nucleophilic. This is particularly likely when the ligand is co-ordinated to a non-labile metal centre. However, even in these cases, all is not lost. We may also use the enhanced acidity of ligands co-ordinated to a metal centre to generate reactive nucleophiles which would not otherwise be readily accessible. For example, nickel(n) complexes of deprotonated diamines may be prepared, and react with dialkylating agents to yield macrocyclic complexes (Fig. 6-10). To clarify this, consider the reaction in Fig. 6-10 in a little more detail. The amine 6.14 is reactive and unselective, and does not give the desired macrocycle upon reaction with the ditosylate. Deprotonation of the amine under mild conditions is not pos-... 

The tetranuclear magnesium chelate complexes [(NH4)4n Mg4(L10 n)6 ] (29a,b) were first synthesized by reaction of dialkyl malonate 28, methylmagnesium iodide, and oxalyl chloride, followed by workup in aqueous ammonium chloride solution [102-105]. Now methyllithium/magnesium chloride instead of methylmagnesium iodide (direct method) is used, which by mere replacement of magnesium chloride by the chlorides of manganese, cobalt, and nickel also allows the synthesis of the corresponding tetranuclear complexes 29 (with Mn = Mn2+, Co2+, Ni2+) [103, 105]. 

Nickel tetracarbonyl undergoes a rapid oxidative addition of the Si-Si bond of 1, highly strained fluorinated disilane, at room temperature to give ffve-membered cyclic bis(organosilyl)nickel(II) complex 2, which then reacts with terf-buty-lacetylene to give six-membered disilacyclohexadiene derivatives 3 as a mixture of the regioisomers (Eq. 1) [10]. A similar bis-silylation reaction of alkynes with bis(organosilyl)nickel(II) complex has been reported in the reaction of bis(trichlorosilyl)(bipy)nickel(II) (bipy 2,2 -bipyridyl), which is prepared by dialkyl(bipy)nickel(II) with trichlorosilane [11]. 

A number of cyclopentadienyl nickel(II) bis(phosphonato) complexes have been prepared by the reaction of bis-(cyclopentadienyl)nickel(II) with dialkyl H-phosphonates [432,433],... 

In 1970, Tavs reported the first nickel-catalyzed arylation of trialkyl phosphites or dialkyl aryl phosphonites with aryl bromides [242] (Scheme 20.72). In this reaction, trialkyl phosphite, a phosphorylating agent, plays a crucial role in the reduction of Ni(II) to active Ni(0) complex [243]. 

Insertion of carbon monoxide followed by reductive coupling is an old reaction that continues to be studied and developed. Examples of this reaction are the carbonylation of nickel dialkyl complexes to give ketones, " alkyl-alkoxides to yield esters, and alkyl-amides to give organic amides (Equation (79)). The carbonylation of the binuclear complex 145 leads to the formation of an isoquinolone ring with the elimination of one of the two Ni atoms, but no GO insertion occurs at the second metal moiety. Hydrolytic cleavage of the remaining Ni-G bond provides the free heterocyclic base (Scheme 45). ... 

Inoue Y, Itoh Y, Kazama H, Hashimoto H (1980) Reaction of dialkyl-substituted alkynes with carbon dioxide catalyzed by nickel(O) complexes. Incorporation of carbon dioxide in alkyne dimers and novel cyclotrimerization of the alkynes. Bull Chem Soc Jpn 53 3329-3333... 

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