Insertion involving isonitriles

Many novel cluster compounds have now been prepared in this way, including mixed metal clusters. Further routes involve the oxidative fusion of dicarbon metallacarborane anions to give dimetal tetracarbon clusters such as (103) and (104) O (jjg insertion of isonitriles into inetallaborane clusters to give monocarbon meiallacarboranes such as (105) and the reaction of small ii/t/o-carboranes with alane adducts such as Et3NAlH3 to give the commo species (106) ... 

Other insertions may involve isonitriles, alkynes, alkadienes, CO2, and SO2. They will not be dealt with here. 

In the insertion reactions, isonitriles may serve as effective ligands on palladium ) for the activation of Si-Si bonds and, at the same time, they are involved as reactant. In contrast, ferf-alkyl isonitriles, which do not insert into Si-Si bonds at all, can exclusively serve as spectator ligands for highly effective activation of Si-Si bonds [46]. 

Loss of PhH by reductive elimination, binding of substrate via the iso-nitrile C, cyclometallation of the ArCH3 group, migratory insertion involving the isonitrile, isomerization and reductive elimination of the product. 

Besides the above-mentioned hving polymerizations mediated by the organopalladium(II) halides, successive insertion of isonitriles into sulfur-sulfur bonds catalyzed by palladium complexes was recently reported (Scheme Thus, in the presence of Pd(PPh3)4, reaction of di-p-tolyldisnlflde with 4.7 equiv of p-tolyl isonitrile afforded a mixture of ArS(C=N—Ar) SAr (Ar = p-Tol, n = 1-9) in good combined yield. Mechanistic investigations revealed that the ohgomerization may involve a reversible oxidative addition of S—S or S—C bonds onto the pahadium, foUowed by insertion of isonitriles into the resultant S— Pd or C—Pd bond, and subsequent reductive ehmination(Scheme 13). 

Usually, an isonitrile can be inserted without transmetalation. As shown in Eq. 2.67, Majoral et al. have isolated and characterized by X-ray analysis the intermediate involved in isonitrile insertion into zirconaindene complexes [47]. 

Elimination reactions are typically found in transition metal chemistry. The conversion of allylic ethers into allylzirconocenes [18] is a well-known zirconium-mediated process of this type. In contrast, the y-elimination reactions are less frequently encountered, and only a few examples of y-elimination involving zirconocenes have been reported. When studying isonitrile insertion into zirconacycles, Whitby and coworkers observed an interesting reaction leading to a cyclopropane derivative [19]. The overall transformation is depicted in Scheme 12. Treatment of the diene 18 with preformed butene-zirconocene gave... 

The tetrameric o-(dimethylaminomethyl)phenylcopper, which is similar to (III) and probably possesses the same structural features, forms monomeric complexes with l,2-bis(diphenylphosphino)ethane and -ethylene but not with triphenylphosphine (281e). Insertion of an isonitrile into the aryl—Cu bond occurs rather than formation of a complex (281d). The new copper compound is dimeric in benzene, and a six-membered ring structure involving heteroatom coordination bonding as in (V) is proposed. Triphenylphosphine breaks down the dimer (V)... 

An intramolecular reaction of 1,5- and 1,6-enynes with isonitriles takes place in the presence of Ni(COD>2 (COD = 1,5-cyclooctadiene) and phosphines, giving bicyclic cyclopentenone imines (equation 5). Stereochemical characteristics in substituted systems appear to pardlel those in the intramolecular Pauson-Khand enynes with substituents in propargylic positions cyclize preferentially to products in which those substituents occupy exo positions relative to the newly created ring fusion. It is likely that these reactions proceed via similar mechanisms involving insertion into bonds of metallacycles, although the order of incorporation of the three two-electron systems into the precursor to the final product is open to question in the nickel system. 

An unusual multiple insertion of bulky isonitriles occurs with [(C6H5)3P]2PdHCl to give [RN=CH=C)4](RN=C)PdCF . Although it is reasonable to assume that the initial step of this reaction is a 1,1-insertion, no intermediate species are observed. The pronounced effect of added tertiary amines on the rate and yield of these reactions also suggests that a deprotonation is involved. 

The reduction of the isonitrile carbon to CH4 and to C2- and Ca-hy-drocarbons is readily accommodated by an alternating reduction and insertion mechanism involving a metal. 

Migratory insertion and its microscopic reversal, that is, migratory deinsertion, are two of the 20 or so fundamental processes discussed in Sect. 1.2 in which Pd participates. In principle, they should be observed with a wide variety of substrates. In reality, however, the current scope of these processes observable with organopalladiums is almost totally limited to those that involve CO and related compounds, such as isonitriles. Conse-qnently, the migratory insertion-deinsertion chemistry of organopalladium compounds at present is essentially synonymous with their carbonylation-decarbonylation reactions. 

Migratory Insertion Reactions Involving CO, CO2 or Isonitriles. DF calculations on the reaction of CO with Cp2ZrMc2 show that CO binds laterally and... 

Square planar / -complexes of rhodium are known for engaging in catalytic cycles based on oxidative addition chemistry. A recently developed example is reaction (5), involving insertion of an isonitrile into an aryl C —H bond. " Initial dissociation of phosphine is likely, providing 14-electron [RhCl(L)(CNR)]. The [Cp Re(CO)L] fragment was very readily produced... 

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