Molybdenum complexes reaction with isocyanides

A more complex reaction is involved in the cooligomerization of acetylenes and tert-butyl isocyanide using nickel acetate as the catalyst (Scheme 20)43 the nature of intermediate complexes leading to the formation of 2-cyano-5-terf-butylaminopyrroles has not been established. Cocyclization of tert-butyl isocyanide with coordinated hexafluoro-2-butyne gives rise to coordinated cyclopentadienone anils for molybdenum systems,44 hence the nature of acetylene substitutents and of the organometallic catalyst play crucial roles in these processes. The pyrrole products from the former reaction can be decomposed by sulfuric acid and the overall sequence provides a simple synthesis of 5-amino-2-cyanopyrroles (Scheme 20). 

A number of attempts have been made over the years to develop reproducible synthetic routes to six- and seven-coordinate isocyanide complexes of molybdenum and tungsten. Two of the older methods, namely, the reaction of the hexacarbonyls with halogens in the presence of an isocyanide (775,116) or reactions of the salt Ag4Mo(CN)8 with isocyanides (74), have given six- and seven-coordinate products. Recently, however, the discovery of the reductive or nonreductive cleavage of multiple metal - metal bonds in dinuclear group VIA compounds by isocyanides has provided a facile route to the synthesis of a variety of homoleptic and related isocyanide complexes of these metals in reasonable yields. 

Molybdenum(IV) and tungsten(IV) compounds may be obtained by alkylation utilizing RX, while reactions of [M(CN)g] with isocyanides RNC lead to complexes in lower oxidation state. 

In a three-component reaction, a cationic platinum isocyanide complex [(Ph3P)2Pt(CNR)Cl][BF4] is reacted with a /3-bromoamine and butyl lithium to give an imidazoldin-2-ylidene complex.This transformation can be a two-component reaction if the isocyanide ligand contains already the necessary amine functionality. This was shown for chromium, molybdenum, tungsten, and rhenium carbonyls. 

The rearrangement of a tungsten carbonyl-complexed 7-phosphanorbomadiene to its 7-phosphatricyclo[3.2.0 ]hept-2-ene complex has been analysed by ab initio MO calculations, and it has been shown that the reactions of molybdenum and tungsten metallates of the type [CpM(CO)2CNR] with methyl iodide yield methyl complexes of the composition [CpM(CO)2(CNR)], which subsequently rearrange to / -iminoacyls and / -l-azaallyls depending on the nature of the metal, the isocyanide R substituent, and the solvent used. ... 

---