Isonitrile Insertion

CH3)3Si)2N]2U(CH2Si((CH3)2)N(Si(CH3)3)) Generally, uranium metaUacycles are quite reactive inserting a host of organics, ie, CO, secondary amines, nitriles, isonitriles, aldehydes, ketones, and alcohols. 

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) ... 

The formation of the 2,3-diiminosulfoxide 152 by the insertion of two moles of isonitrile into the carbon-sulfur bond of 30164 (equation 61) can be naively considered as related to the transformation 16a -> 147 -> 148. 

This photodriven benzannulation was used in the synthesis of indolocar-bazoles (Eq. 22) [96] and calphostins (Eq. 23) [97]. The thermal insertion of isonitriles into these same classes of carbenes provided a complementary approach to similar benzannulations [98-100]. Manganese alkoxycarbene complexes underwent both inter- [101] and intramolecular [102] photodriven benzannulation reactions with alkynes (Eqs. 24 and 25). 

Note that carbon monoxide inserts into the Zr-H bond of 1 (2 equiv.) to afford an T -formaldehydo-type complex [(Cp2ZrCl)]2(g-CH20) [200-202]. Iminoacyl zir-conocene complexes are formed after addition of 1 to isonitriles [203]. Carbon dioxide [183, 202] is reduced to formaldehyde with 1 (2 equiv.). C02-like molecules such as isocyanates RNCO [204], isothiocyanates RNCS [205], and carbodiimides RNCNR [204] are readily converted to the corresponding bidentate form-amido ligands. 

A very common combination in Pd-catalyzed domino reactions is the insertion of CO as the last step (this was discussed previously). However, there is also the possibility that CO is inserted as the first step after oxidative addition. This process, as well as the amidocarbonylation, the animation, the arylation of ketones, the isomerization of epoxides, and the reaction with isonitriles will be discussed in this section. 

The indazoline products can also be made directly from the palladium complexes 78 by heating them with the isonitrile in toluene at 120CC.162 They are also formed in dicobalt octacarbonyl-catalyzed reactions of azo-arenes with isocyanides but in this case an alternative reaction pathway leading to indazolo[2,l- ]indazoles (79) is observed (Scheme 96).163 Products of the latter type are formed from sterically hindered isocyanides hence it is likely that in these cases a double metallation is favored over isocyanide insertion into a monometallated species (Scheme 97). 

Based on the established mechanism for titanium-catalyzed hydroamination, the authors propose a reversible reaction between a titanium imide complex and the alkyne to form metalloazacyclobutene 86, which in turn undergoes 1,1-insertion of the isonitrile into the Ti-C bond. The generated five-membered ring iminoacyl-amido complex 87 with the new C-C bond is protonated by the primary amine to afford the desired three-component coupling product, with regeneration of the catalytic imidotitanium species. Very recently, titanium-catalyzed carbon-carbon bond-forming reactions have been reviewed.122... 

This transformation proceeds through coordination of the isocyanide group to the ruthenium complex (structure 172), followed by insertion of the C-bound ruthenium into the benzylic C-H bond (intermediate 173). After ruthenium-mediated addition of the benzylic carbon to the isonitrile carbon and tautomerization, the desired product was obtained via elimination of the ruthenium complex. 

Rhodium-catalyzed reactions of diynes and an isonitrile give rise to iminocyclopentadienes (Equation (68)).421 Portionwise addition of the isonitrile (5 x0.2equiv.) was found to increase the yield. The reaction may proceed through formation of metallacyclopentadienes followed by insertion of an isonitrile molecule. 

Interestingly, by using an alcohol (S.Oequiv.yBu ONa (1.2 equiv.) instead of an alkoxide (5.0 equiv.), double isonitrile insertion takes place to give a-iminoimidates (Equation (120)).479... 

Dimethyl-4-methylene-l,3-dioxolan-2-one reacts with isonitriles in the presence of a palladium catalyst to afford iminofurans (Equation (121)).480 Successive insertion of isonitriles to the carbon-palladium bond of 7r-allylpalladium intermediate is postulated. 

The 2,3-substituted indols are formed via a palladium-catalyzed coupling reaction of aryl halide, o-alkenylphenyl isocyanide, and amine (Equation (122)).481 Oxidative addition of an aryl halide, insertion of both the isonitrile and alkene moieties of o-alkenylphenyl isocyanide, and 1,3-hydrogen migration may form a 7r-allylpalladium species, which is then attacked by an amine to afford an indol. 

Scheme 1.37. Common patterns in the migratory insertion of zirconocene complexes with CO, isonitriles, and metal alkynylates.

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]. 

In this chapter, we provide the necessary background concerning the formation of zir-conacycles, then briefly review the insertion of carbon monoxide and isoelectronic isonitriles into organozirconocenes. We then describe in more detail the insertion of a-halo-a-lithium species (R1R2CLiX, carbenoids [7]), which may be viewed as taking place according to a conceptually similar mechanism. 

The synthesis of analogous iminoacyl complexes by isonitrile insertion into linear alkyl-zirconocene chlorides is also known. In an overall regiospecific hydrocyanation of alkenes, iminoacyls 21 derived from tBuNC or Me3SiCN (as the Me3SiNC isomer) may be treated with I2 to rapidly generate an imidoyl iodide and subsequently the nitrile 22 (Scheme 3.6) [22], Less hindered iminoacyl complexes (e. g. R = Bu, Cy) may be hydrolyzed to afford aldehydes 23 [23]. 

Isonitrile insertion into zirconacycles to afford iminoacyl complexes 28 is fast, but rearrangement to q2-imine complexes 30 is slow. In the case of tBuNC, the rearrangement does not occur. Amines 32 are formed on protonolysis of the q2-imine complex. The q2-imine complexes 30 readily undergo insertion of Ti-components (alkenes, alkynes, ketones, aldehydes, imines, isocyanates) to provide a wide variety of products 37 via zirconacycles 36. The overall sequence gives a nice demonstration of how a number of compo-... 

Scheme 3.7. Carbonylation and isonitrile insertion into zirconacycles.

Mechanisms of the manifold reactions of a-dialkylamino alkyllithium intermediates R(Me2N)CLiNu, formed when tertiary amides (RCONMc2) react with PhMc2SiLi followed by a second lithium reagent NuLi, have been discussed. The formation of diverse products following 1 1 insertion of an isonitrile RNC into the Li-C bond of LiCH(SiMc3)2 has been discussed. ... 

CO is a representative species for n.o-insertion its insertion into C—Pd bonds affords acylpalladium complexes such as 15. Mechanistically, the CO insertion is 1.2-alkyl migration to coordinated CO. This is an important step in carbonylation. SO , isonitriles, and carbenes are other species which undergo a.a-insertion. 

Isonitriles react with oligo- and disilanes or silylstannanes to yield 1,1-addition products in which both Group 14 elements add to the same carbon atom of the substrate rather than across the C-N triple bond. Ito and coworkers report that palladium complexes, such as Pd(PPh3)4 and Pd(OAc)2, effectively mediate these insertion reactions, an example of which is shown in Eq. (27).78... 

In the same vein, several examples of stoichiometric hydride migration to coordinated olefins have been observed (90, 9/) corresponding alkyl migrations (which should be more favorable based upon a Scheme 5-type analysis) have not yet been noted to occur (91). Bercaw has reported the insertion of an isonitrile (subsequent to initial coordination) into a zirconium-hydrogen bond to yield the imino formyl derivative 62 [Eq. (36)] (92). 

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