Ketenimine complexes

The reaction of [p-MeC6H4C(NSiMe3)2]2Ta( = CH2)CH3 with 2,6-dimethyl-phenyl isocyanide afforded an f/ -ketenimine complex (Scheme 118). Carbon-sulfur cleavage reactions produced tantalum thioformaldehyde and tantalum sulfido complexes. ... 

A similar mechanism may be invoked to explain the reaction of 47 with isocyanides in which ketenimine complexes are formed (39) ... 

Let us first consider the reaction between vinylketene complexes and phosphoramidate anions.90,134 Deprotonation of the appropriate phos-phoramidate with Bu"Li affords the corresponding phosphoramidate anion (232.a-232.c), which undergoes a Wadsworth-Emmons type reaction on the ketene carbonyl to afford the ketenimine complexes 233. Ketenimine complexes may also be prepared by the thermolysis of the vinylketene complexes (221) with isonitriles (vide infra).69... 

KCl, dissolution process, 39 416 Ketab, synthesis, 30 263 Ketenimine complexes with iron, 12 245 KetiminoberyIlium halides, preparation and properties of, 14 307-308 a-Keto acid, formation, 43 427-428... 

Although ketenimines are not known to dimerize to cyclobutane derivatives, certain metal coordinated ketenimines have been reported to undergo thermal dimerization to give cyclobutane-1,2-diimines. The chromium ketenimine complex 19 dimerizes to complex 20 in 60-80% yields.60 b... 

The metal-free eyclobutane-1,2-dioxime can be generated by oxidative displacement. It is interesting to note that, unlike ketene dimerization, head-to-head dimerization takes place here. The chromium ketenimine complex 20 is prepared by reaction of the Fischer-type chromium carbene complex with alkyl isocyanides.60 A cyclobutane-1,2,3,4-tetraimine 24 has been reported from the reaction of the ketenimine phosphonium ylide 22.61 Bisimine 23 has been proposed as the intermediate in this transformation. 

The intermediate Ni(CNBu )3 N2C(CN)2), formed by adding diazodi-cyanomethane to Ni(CNBu )4, rearranges, probably via a carbene insertion, to give the ketenimine complex Ni Bu N=C=C(CN)2 (CNBu )2. An X-ray structural determination of the product has been reported (436). 

C-H bond dissociation energies, 1, 298 C-N triple bond additions, 10, 427 C02, ketene, ketenimine complexes, 5, 84 CO and CNR reductive coupling, 5, 66 cyclopentadienyl alkyl and aryls, 5, 66 cyclopentadienyl carbonyl complexes, 5, 64 cyclopentadienyl hydrides, 5, 69 cyclopentadienyl isocyanide complexes, 5, 65 rf-acyl and rj2-iminoacyl complexes, 5, 82 fj3-complexes, 5, 87... 

Structures of type XVIII or XIX as proposed for the diazodicyanomethane complex (Table 12) may also apply to the complexes of diphenyldiazomethane and 9-diazo-fluorene. The formation of the ketenimine complex (45) from the reaction of (CN)2CN2 and Ni(t-BuNC)4 probably occurs via attack of the complexed dicyano-methylene carbene on the isocyanide ligand113 The observation that these complexes112 113 catalyze the formation of ketenimines from isocyanides and diazo compounds, a reaction which does not proceed under same conditions without the transition metal, may be of preparative value 113 ... 

Few 7r-bonded imine complexes have been prepared and investigated structurally. The only complexes of nonbridging 7r-bonded C=N investigated structurally are a substituted ketenimine complex (XLIV), an iminium complex (XLV), and a complex of the azine [(CF3)2C=N—)2 (XLVI) (see Table I). 

The ketenimine complex is unusual in that angle y for the complex is 11.9(10)° and the average S is 174°. These angles are indicative of a coordinated triple bond, rather than the expected double bond. This seemingly anomalous result can be rationalized on the basis of a large contribution of resonance form B to the structure of the ketenimine. This... 

M/-Enamino)carbene complexes (CO)5M = C(OEt) — CH = CPh (NHR) (Z)-97 (M = Cr, W R = Ph, i-Pr, CH2) add 2 eq of an isocyanide R1—NC (R1 = c-C6Hu, f-Bu) to give ketenimine complexes and finally ketenimines, which are readily cyclized to (air-sensitive) 2-amino-3-ethoxy-pyrroles.121 Galactopyranosyl pyrroles 112 are obtained by this procedure from enantiomeric pure (2-aminoethenyl)carbene complexes (CO)5M =... 

Ketenimine complexes 323 react with carbodiimides to give [2+3] cycloadducts 324 in... 

Ketenimine complexes from carbene complexes and isocyanides as building blocks for N-heterocycles 88AG(E)1456. 

Ketenimine complexes can serve as three-atom components in [3 + 2] cycloadditions. The reaction of the tungsten complex (378) with cyclohexyl isonitrile and phenyl isocyanate produces the heterocyclic carbene complex (379), which is the result of the in situ trapping of a ketenimine complex with the isocyanate. Complexes of the type (379) can be oxidatively cleaved to give the previously inaccessible 5-ethoxyhydantoins. [3 + 2] Cycloadditions of this type have also been carried out with aldehydes. 

Cyclohexylisocyanide adds to the carbene carbon of [Cr C(SPh)CH= CHPhXCO),] (581), causes a rearrangement of the ligands and the formation of an S-coordinated ketenimine complex, 606 (3/6). 

The zirconocene bis(phosphine) complex, 57, also coordinates Ar N-C=CPh2 (Ar = >-MeC6H4) to yield the zirconocene ketenimine derivative (r]5-C5H5)2Zr(r]2-(C, j/V)-Ar N=C=CPh2)(PMe3) 61 with loss of phosphine (Scheme 9). Similar chemistry is observed upon reduction of (775-CsMe5)2ZrCl2 53 with LiBuc in the presence of the ketenimine.24 However, in the latter example the base-free ketenimine complex is isolated. 

Tungsten ketenimine complexes react with isocyanates to give [3+2] cycloadducts (see Chapter 4, Section 4.3). 

Ketenimine complexes, such as R(OMe)C=C=N(R ) Cr(CO)5, 3, which can be generated from a carbene complex and an isonitrile, dimerize in the metal template to form the blue dimer complexes 4. The formation of the unexpected dimer is caused by the metal template... 

Similar ketenimine dimer complexes are also obtained from molybdenum and tungsten ketenimine complexes. 

The ketenimine complexes 100 react with aldehydes, isocyanates and carbodiiinides to give the [3+2] cycloadducts 101. ... 

The reaction of isocyanide with electron-rich cyclopentadienyl cobalt(l) complexes has led to the formation of the substitution products 40, 43, and 46, which even at RT underwent oxidative addition to give the compound 41. This study showed that the choice of the isocyanide ligand is important to induce this reaction. The /> 7ra-tolylisocyanide did not react by C-N bond cleavage. The complexes formed from the substitution of one phosphine by an isocyanide reacted with diphenyldiazomethane to give the C,C-bound ketenimine complexes 42, and 44. The />-tolylisocyanide... 

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