Isocyanates, addition isonitriles

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. 

Several new complexes of iminophosphoranes have been reported by Cavell and co-workers (Scheme 9). Reaction of dimethyl zinc with bis- trimethylsilyl-imino-diphenylphosphorano methane (61) yields zinc complex (62) via elimination of methane. Complex (62) did not react with adamantyl nitrile or isonitrile but does undergo nucleophilic addition reactions with hetereroallenes such as carbodiimides and isocyanates. Thus, treatment of (62) with adamantyl isocyanate produces the novel tripodal alkyl zinc complex (63). Iminophos-phorane (61) reacts with [Sm(NCy2)3(THF)] and tetrakis(benzyl)zirconium(IV)... 

The compound reacts with alcohols, phenols and amines to form products similar to those obtained from the corresponding reaction with COCI [1358]. Depending upon the conditions and stoicheiometry, carbonates and chloroformates [612,1380], carbamates [1380], isocyanates [1184] and ureas [938] can be obtained with diphosgene, in addition to more complicated products such as carbamoyl chlorides, imidic chlorides, carboxylic acid chlorides, isonitriles and IV-carboxy-Q-amino acid anhydrides [1358]. 

During experiments to trap a reaction product of a nitroso compound and isonitrile with an alkyl isocyanate, an additional way of formation of diaziridinimines was discovered. Besides some other heterocycles the five-membered ring compound 138 was formed, which yielded 133 by extrusion of carbon dioxide at 150°. ... 

Sulfoxonium salts react with hard bases at sulfur and with soft nucleophiles at the oxygen end. Although the acid-catalyzed oxidation of isonitriles to isocyanates (139) has been formulated as involving an a addition of H and DMSO at the carbon atom of the isonitrile, the alternative mechanism shown below appears more viable in the HSAB context. 

Isonitriles also undergo carbene-like reactions with isocyanates and coreagents. For example, two isomeric [1+2+2] cycloadducts 50 and 51 are obtained from nitroso compounds, isonitriles and isocyanates. The reaction proceeds via addition across both the C=N and the C=0 bonds of the isocyanate . 

The various classes of compounds featuring carbon-nitrogen multiple bonds that are substrates for organometallic addition comprise azomethines, immonium ions, nitrones, hydrazones, oxime ethers, amidinesimidoyl halides, nitriles, isonitriles, and cyanates. Dicyclohexylcarbodiimide is omitted here because it has been included in the carbonyl section (p.l 16) side by side with isocyanates and isothiocycanates. 

---