Alkyls, Carbenes, Carbynes, and Carbides

Although there are some early examples of complexes in which M—C single bonds are present (e.g., Me3PtI 4 synthesized in 1907), the prevailing view for many 

A great deal of synthetic success has been achieved by using alkyl groups that do not have hydrogen atoms. Among these are PhCH2, Me, and CH2CMe3, none of which can decompose by fi elimination. 

The syntheses of transition metal alkyls can be accomplished in several ways. A common approach is to take advantage of the nucleophilicity of a carbonylale ion.59 For example  

In this reaction [Mn(CO) ], which is quite nucleophilic, increases its metal coordination number by one. The reaction may be viewed as an electrophilic attack by R on the metal. Similarly, it is possible to prepare bridging alkyl complexes by this method 60 

A second approach involves a nucleophilic attack on the metal. This is seen in the reaction of methyl lithium with tungsten(VI) chloride  

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Metal Alkyls, Carbenes, Carbynes, and Carbides Alkyi Complexes... 

Veillard [19] covers a similar range of molecules but from the Hartree-Fock and post-HF view. The discussion is organised more in terms of molecular properties. Thus, he deals with metal carbonyls, carbides, cyanides, C02 complexes, alkyls, carbenes, carbynes, alkenes, alkynes and metallocenes under the headings of electronic states, electronic spectra, optimised geometries, binding energies, Ionisation Potentials and Electron Affinities, nature of M-L bonding and other properties (e.g. vibrational spectra, dipole moments and electron distributions). 

The ultimate member of the series alkyl (-CR3), carbene (=CR2), and carbyne (=CR) is the carbide18 ligand, C. Although it is tempting to represent this, by extension, as quadruply bonded = C, this ligand, when attached to transition metals, is probably best considered =C. The first transition metal carbide complex to be reported was the anion [C=Mo N(C(CD3)2Me)(3,5-Me2(C6FI3) 3], shown in Figure 6-7.19... 

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