Isocyanide multiple insertion

Successive multiple insertions of an aryl isocyanide (ArNC) into the S-S bond of a diaryl disulfide (ArS)2 occurs in the presence of Pd(PPh3)4 to produce the corresponding poly(imino)alkane endcapped with an arylthio group (Equation (65)).167 Products of higher molecular weights are formed when isolated poly(imino)alkanes are again subjected to the conditions of the insertion reaction (up to n — 9). 

Isocyanides are more reactive than CO, and multiple insertions into M—C bonds are a common occurrence. 

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. 

Polymerization of isocyanides is a thermodynamically feasible process, in agreement with the stoichiometric multiple insertion observed in reactions between metal-alkyl complexes and isocyanides. The entropy loss in the case of isocyanides is lower than for insertion of CO. Isocyanide insertions into palladium-alkyl a bonds are faster than those for the platinum(II) analogues. The latter, on the other hand, usually lead to more stable and better defined products. Insertion of isocyanides into platinum-carbon bonds has been studied extensively Reaction (j) is typical the ionic product was strongly suggested by observation that the compounds isolated under mild conditions are 1 1 electrolytes. 

The first multiple insertion of isocyanide into the Pd-C bond of organopal-ladium complexes was reported by Yamamoto in 1970 (Scheme 21) [30]. The reaction of one, two, and three equivalents of cyclohexyl isocyanide with the trans-iodobis(phosphine)methylpalladium(II) complexes 17 yielded the monoimino (18), bisimino (19), and trisimino (20) palladium complexes, re-... 

In contrast to the case of CO insertion that usually allows insertion of only one CO unit into a metal-carbon bond, isocyanides undergo multiple insertions sometimes leading to polyisocyanides [53,54]. Since the inserted isocyanide units may be regarded as imines derived from carbonyl groups, the insertion products can be regarded as polycarbonyl compounds where CO units are multiply inserted into the metal carbon bonds. The multiple insertion products of isocyanides have found applications both in organic synthesis and polymer synthesis [55]. 

Polymerization of isocyanide by multiple insertion into metal-carbon bond... 

The insertion ability of isocyanides differs from that of CO. In contrast to the carbon monoxide, for which consecutive CO insertion is disfavored, isocyanides readily undergo the multiple insertion processes especially with more nucleophilic metals such as Ni and Pd (Eq. 7.14). The multiple insertion may lead to new types of organic compounds difficult to prepare by other synthetic methods. 

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. 

Little is known about the reactivities of complexes having zirconium-silicon bonds. Reaction of lb with hydrogen chloride afforded triphenylsilane (Scheme 3) [16a]. The insertion of carbon monoxide or isocyanide into a zirconium-silicon bond of lc gave silaacylzirconium complex 4 or iminosilyl-zirconium complex 6 [17b,c]. As for carbon-carbon multiple bonds, ethylene can be inserted into a zirconium-silicon bond of lh [17g],but other multiple... 

Examples of multiple isocyanide insertions into Pd—C,173 Pd—H,174 and even Pd-S,175 bonds are compounds (21-XXXVI) - (21-XXXVIII) ... 

The uranium-carbon multiple bond has an extensive insertion chemistry with polar unsaturated molecules including carbon monoxide, nitriles, isocyanides,and isocyanates. Metal carbonyls also insert into this bond to form metallaphosphoniumenolates, which undergo novel reactions... 

Transition-metal-catalyzed hetero-[2 + 2 + 2]-cy-cloaddition of alkynes with carbon—heteroatom multiple bonds, such as isocyanides, carbon dioxide, nitriles, aldehydes, and ketones, provides heteroare-nes and unsaturated heterocycles. This reaction can be categorized into two groups one is the reaction of l,a>-diynes 397 with carbon—heteroatom multiple bonds, and the other is reaction of the alkynes 399, having a carbon—heteroatom multiple bond with alkynes as illustrated in Scheme 127. The reaction of 1,6 -diynes 397 proceeds through formation of the metalacyclopentadiene intermediate 398 followed by insertion of a carbon—heteroatom multiple bond, such as heterocumulenes (route a),189 nitriles (route b),190 and carbonyls (route c).191 On the other hand, the... 

A novel route to polymer chains 5.20 that contain metal moieties as terminal groups has been reported, which involved multiple (up to 100) insertions of aryl isocyanides into the Pd-C bond of the heterodinuclear /r-acetylide complex [Cl(PR3)2Pd-C = C-Pt(PR3)2Cl] (Eq. 5.12) [35]. Crosslinked Pt[Pg.159]

The C-N multiple bond of an isocyanide is weaker than the C-O multiple bond in CO. Thus, the insertion of an isocyanide into a C-H bond in a reaction that is analogous to the carbonylation of C-H bonds should be more favorable thermodynamically. An example of this reaction catalyzed by [RhCl(CO)(PMe3)j] under photochemical conditions is shown in Equation 18.34. A more efficient, albeit more complex, reaction of an isocyanide involves intramolecular insertion into the o-methyl group in 2,6-dimefhylphenylisocyanide, whidr leads to an indole product in high yield (Equation 18.35). ... 

---