Insertion reactions of isocyanides

The work on insertion reactions of isocyanides was initiated by Yamamoto et ah, and described in a communication in 1968 followed by a full paper a year later (164). This study described the reaction of C5H5Ni(PPh3)CH3 with several isocyanides, from which the products C5HjNi(CNR)- C(=NR)CH3 were isolated [Eq. (2)]. 

The insertion of isocyanides provides another example of this reactive behavior. Insertion reactions of isocyanides and heteroallenes carried out with the tripod-stabilized early-late heterodinuclear complexes (represented in Figure 4.5) that led to stable products are summarized in Scheme 4.8. 

Insertion reactions of platinum(II) alkyl and aryl complexes (144, 153, 171), nucleophilic displacement of isocyanide from [Pt(PRj)2(CNCH3)2] (147) and additions of alcohols and related substances to isocyanides bonded to platinum (8, 9, 25, 33, 34, 100, 117) were discussed earlier. 

This reaction appears to be similar to the imidazo-pyridine formation mentioned above, most likely via a [5+1] insertion reaction of the isocyanide into the corresponding hydrazone. This reaction mechanism seems likely since only electron-rich aromatic hydrazines yielded cinnolines. The Ugi 4-CR reaction with phe-nylhydrazine is known and has been reported to give the expected Ugi-type 4-CR product. 

A mononuclear tantalum-benzyne complex (121) has been prepared by thermolysis of 120 [Eq. (20)].14 An X-ray crystal structure was reported for 121. Bond lengths for the benzyne unit are given in Table III. Complex 121 exhibits a rich insertion chemistry similar to that of Ti, Zr, and Ru benzyne complexes. Insertion reactions of 121 with ethylene, 2-butyne, acetonitrile, and carbon dioxide give 122, 123, 124, and 125, respectively (Scheme 15). Diphenylacetylene does not couple with 121, presumably because of steric constraints. Reagents with acidic protons such as methanol or terminal alkynes cleave the Ta—C bond to give butyl isocyanide and carbon monoxide, but... 

Finally, although not a reaction of isocyanide complexes as such, except as labile intermediates, it can be noted that metal hydrido or alkyl compounds can undergo insertion reactions to give acylimidoyl complexes, which can react further ... 

The insertion reactions of alkyl and aryl isocyanides were recently reviewed 126, 142) and will not be treated exhaustively in the present article. 

Another application of pure organocopper compounds is as starting materials for the synthesis of other organocopper compounds. Treatment of [CuCisHjCFj-3] with (CF3)sCBr, for example, affords CuC(CF3)3 throu a halogen/metal exchange reaction [73] (Eqn. 2 in Scheme 1.12). A further demonstration of the applicability of pure organocopper compounds is the insertion reaction of an isocyanide into a copper-carbon bond [74], (Eqn. 3 in Scheme 1.12). 

Insertion reactions of small molecules into the Sc-Si bond of the Sc " compound [(r -CjH5)2(THF)ScSi(SiMe3)3] (101) are also worthy of note, and parallel some related transition meted chemistry [133c]. For example, 101 reacts with aryl isocyanides (ArNC) initially via insertion into the Sc-Si bond giving intermediate r -iminosilaacyl compound 102, which then reacts further by the proposed mechanism shown in Scheme 14.7 to give the fused ring compound 103. 

Legzdins P, Rettig SJ, Ross KJ (1994) Competitive reactivity of W-C, W-N, and W-O bonds at the Cp W(NO) fragment insertion reactions of tert-butyl isocyanide, p-tolyl isocyanate, and carbon disulfide. Organometallics 13 569-577... 

The Pt-P bonds of these complexes are very stable, as there was no evidence of insertion of CO, CS2, white phosphoms or ethyl diazoacetate into the Pt-P bonds or reaction with Mel. These reactions led either to formation of cyc/o-(P4Mes4) and cyclo-(P3Mes3) or to unidentified products with no apparent insertion reaction. In addition, the proposed insertion reaction of 38 and 39 with terf-butyl isocyanide and... 

A). The alkyl complexes react rapidly with CO and isocyanides, but pure products could not be isolated. Fast reactions of CO2 and acetone with Sc(OEP)Me gave the well-characterized acetate and /-butoxide products. Sc(OEP)OAc and Sc(0EP)0-r-Bu, respectively, formed by insertion into the Sc—C bond. ... 

The subjects of structure and bonding in metal isocyanide complexes have been discussed before 90, 156) and will not be treated extensively here. A brief discussion of this subject is presented in Section II of course, special emphasis is given to the more recent information which has appeared. Several areas of current study in the field of transition metal-isocyanide complexes have become particularly important and are discussed in this review in Section III. These include the additions of protonic compounds to coordinated isocyanides, probably the subject most actively being studied at this time insertion reactions into metal-carbon bonded species nucleophilic reactions with metal isocyanide complexes and the metal-catalyzed a-addition reactions. Concurrent with these new developments, there has been a general expansion of descriptive chemistry of isocyanide-metal complexes, and further study of the physical properties of selected species. These developments are summarized in Section IV. 

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. 

Reactions of Pt(PPhj)2(R)X (R = CH3, C Hj X = Cl, Br, I) and methyl isocyanide 144) and analogous reactions of Pd(phos)2(CH3)I (phos = PPh3, PPhMc2) complexes with cyclohexyl isocyanide 169, 170) were reported about the same time. As might perhaps be anticipated, the platinum reactions were slower and one can isolate the intermediate species and observe their rearrangement to the inserted products [Eq. (8)]. The isolation of the... 

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

A large amount of the work on palladium isocyanide complexes has been mentioned earlier, in discussions on insertion reactions 30,74,108,169,170) and on addition reactions of coordinated isocyanides 25, 33, 34, 49) the reactions of [Pd(CNBu )2] with oxygen 107) and with various olefins 29, 110) were noted. 

Much of the recent interest in insertion reactions undeniably stems from the emphasis placed on development of homogeneous catalysis as a rational discipline. One or more insertion is involved in such catalytic processes as the hydroformylation (31) or the polymerization of olefins 26, 75) and isocyanides 244). In addition, many insertion reactions have been successfully employed in organic and organometallic synthesis. The research in this general area has helped systematize a large body of previously unrelated facts and opened new areas of chemistry for investigation. Heck 114) and Lappert and Prokai 161) provide a comprehensive compilation and a systematic discussion of a wide variety of insertion reactions in two relatively recent (1965 and 1967) reviews. 

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