Isocyanide complexes group 10 metals

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. 

The interests in homoleptic (see Homoleptic Compound) isocyanide ( isonitrile, see Isocyanide Ligands) complexes of transition metals have largely been associated with their similarities to metal carbonyls. The greater versatility of isocyanide ligands in comparison to CO makes isocyanide complexes potentially valuable reagents in synthetic chemistry and catalysis. The dication [V(CNBu )6] reported in 1980 remained the sole example of a homoleptic group 5 metal isocyanide until 1999, when the first binary... 

In this article the term organometallic compound includes alkyl and aryl derivatives of the rare earths—the transition metals of group III, scandium, yttrium, lanthanum and the lanthanides cerium to liitetium with covalent metal-to-carbon a-bonds, as well as the so-called 77-complexes with more than monohapto metal-to-carbon bonds, for example cyclopentadienyl and olefin complexes, metal acetylides, but not carbonyls, cyanides and isocyanide complexes. Derivatives of scandium, yttrium and lanthanum are included and discussed together with the compounds of the lanthanides, because of many similarities in the synthesis and the chemistry of these organometallic derivatives of the rare earths. 

The IR spectra of all isocyanide complexes [MacML] and MacML2 show the intense stretching frequency of the isocyanide group at about 2080-2150 cm (see Tables 10 and 11). The shift of this absorption by changing from free to metal coordinated ligand is attributed to the or-donor and n-acceptor abilities of the metal ligand bond. The strength of the jt-acceptor bond... 

In many cases, it was found that the lowering of the v(C = C) frequency is also accompanied by lowering of the v(CO) or v(CN) in olefin-carbonyl or olefin-isocyanide complexes. Therefore, better n redonor properties of the metal with respect to CO groups cause an increase of n interaction with olefins. The Av(C = C) value is not always... 

For the functionalized isocyanide compounds [(CO)5M(o-R3PCH2C5H4NC)]Bp4, the oxidation potentials are only marginally higher than those commonly found in related non-functionalized aromatic isocyanide complexes, thus indicating that the phosphonium group has not a substantial effect on the metal-centred anodic process, possibly as a result of its distance to the metal. 

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