Nickel isocyanide insertion

In the reaction of Ni(CNBu )4 and methyl iodide oligomerization of the isocyanide was observed the only isolable nickel complex was (I), shown below. This product is believed to arise through sequential insertions of three isocyanides into a nickel-carbon bond. Upon further treatment with additional isocyanide at a temperature greater than 60° C one obtains a polymer (RNC) presumably through multiple isocyanide insertion reactions. The addition of benzoyl chloride to Ni(CNBu )4 gave two isolable compounds Ni(CNBu )3(COPh)Cl (74%) and (II) (8.2%). This latter reaction, and the isolation of (II) in particular, suggests that the proposed mechanism for polymerization of isocyanides is reasonable. 

Isocyanide insertion reactions have been studied extensively for nickel, palladium, and platinum complexes. As early as 1968, cyclohexylisocyanide was reported to insert into the nickel-carbon bond of Ni(fj -C5Hs)R(PPh3), giving the following cyclo-hexylimino derivatives ... 

Disubstituted isocoumarins arise from the copper(II)-catalyzed addition of o-halobenzoic acids to active internal alkynes (13JOC1660), rhodium(III)-mediated oxidative coupling ofbenzoic acids with disubsti-tuted alkynes (13T4454), palladium(II)-catalyzed tandem annulation reaction of o-alkynylbenzoates with methyl vinyl ketone (13T8626), and nickel(II)-promoted t-butyl isocyanide insertion in 2-(o-bromophenyl)-1-ethanones followed by hydrolysis (Scheme 69) (13SC3262). 

An a-hydrogen elimination is the microscopic reverse of hydride insertion/imino formyl formation and affords the nickel(ii) hydride complex (c. Scheme 2). Subsequent olefin insertion and isocyanide insertion gives hydrocarbation product (f. Scheme 2). Isotopic labeling experiments by using < 4-ethylene or [Ni C(D)N(D)xylyl (triphos)](CF3S03)2 showed deuterium at both the methylene group and the methyl group of the a-ethyl carbene (f. Scheme 2), not expected in an alkene pathway. 

Mention was made earlier about insertion reactions into nickel alkyl bonds 108, 164), and about polymerizations of oleiins by isocyanide nickel complexes 31,174). 

A3-Pyrrolinones have also been obtained from metal-mediated cyclooligomerization processes in which concomitant hydrolytic or carbonyl insertion occurs. For example, tert-butyl isocyanide is converted in aqueous methanol by zerovalent nickel compounds e.g., Ni(t-BuNC)4, Ni(CO)4, into a di(alkylamino)-A3-pyrrolinone in moderate yield (Scheme 34). The reaction takes a different course in anhydrous methanol in which a di-tert-butylamino)ethylene derivative is formed, albeit in poor yield (Scheme 34).62... 

As stated earlier, (11.3.1), the multiple insertion of carbon monoxide into the same metal-hydrocarbyl bond is a rather elusive reaction. On the other hand, multiple insertion of isocyanide has been reported for nickel(II). For example, when the nickelfO) derivative Ni(t-BuNC)4 was treated with Mel in hexane at RT, consecutive insertion of three RNC groups was observed to give the product of reaction (e), as a consequence of a primary oxidative addition of the alkyl iodide to the nickel(O) complex. It is interesting that one of the two terminal fragments of the five-membered metallacycle is reminiscent of an arrangement of the first insertion product. 

The initiation step of polymerization was studied using the stoichiometric reactions of the (PPh3)CpRNi(II) complexes 3 with isocyanides (Scheme 8) [17, 18]. Insertion of the isocyanides into the carbon-nickel... 

Isocyanides. Several instances for nickel(ii) and palladium(ii) complexes have been suggested. - One interesting feature is that whereas carbon monoxide only inserts once into a given bond, isocyanides can insert repeatedly, providing a potential route for catalytic polymerisation. ... 

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