Transition-metal amides

Cationic transition metal amide complexes have been investigated in part because of their potential in catalysis p irticularly for olefin polymerization. Much of this work has concerned polydentate amido, linked cyclopentadienyl-amido or delocalized nitrogen centred bidentate ligands (see later). However, the structures of a small number of cationic complexes containing monodentate amido ligands have been determined. These include... 

Two other routes to transition metal amides were not generally discussed in the 1980 book. The first of these involves the deprotonation of aminometal complexes as shown in Equation (6.3), which has afforded several new amido complexes. 

Table 6.3 Thermochemical bond energies (kJ mol ) of the M N bonds in some early transition metal amides...

The thermodynamics of the oxidative addition process tends to be favored by increased electron density at the metal centre, hence the focus on later transition metal derivatives. Furthermore, as discussed above, it is believed that M—N n-bonds to the later transition metals are of significance only if the transition metal complex is unsaturated. Saturated late transition metal amides (parent or substimted) often exhibit the so-called n-conflict (see above) so that the nitrogen centre displays no n-bonding to the metal and retains its lone pair character and basicity. 

The use of several new types of amido ligands that are based on a multiplicity of anionic and/ or neutral donor sites has been a major feature of transition metal amide chemistry since around 1930 5-9.17,18.22.23,26,30,31.33.36.37.40.44.46 8,52.53 develop-... 

M. H. Chisholm and I. P. Rothwell, in Comprehensive Coordination Chemistry, ed. Wilkinson, G. Gillard, R. D. McCleverty. J. A., Pergamon Oxford, 1987, vol. 2, p. 161. See also Comprehensive Coordination Chemistry II, ed. McCleverty, J. A. Meyer, T. B. Elsevier, Amsterdam, 2004, vols. 4-6 these chapters cover some aspects of transition metal amides. 

The transition metal amides constitute an extensive series of compounds with widely varying coordination numbers (37, 38). These factors, coupled with... 

This method, sometimes referred to as transmetallation, is by far the most versatile synthetic route to transition metal amide complexes. The amide, typically lithium or sodium, is reacted with the corresponding transition metal halide either in a hydrocarbon or, more typically, an ether solvent. The method has been applied to virtually all of the transition elements and normally results in complete substitution except for the most bulky amido substituents (equations 12,37 13,38 14,39 1540... 

The elimination of amines may also be accomplished by using the reactions of organotin amides and transition-metal hydrides, or transition-metal amides and tin hydrides4. Neither route has attracted much attention recently. 

By analogy with reported Si and Sn reactions, amine elimination by this route (or the reverse using the transition-metal amide) should provide a flexible synthesis for a range of Ge—M bonds, and further development is to be expected. 

Under the attack of one equivalent OH in H2O, MeO in MeOH, or pure NH3 a silicon vertex was removed from the c/oso-cluster l.[21 A plausible mechanistic sequence for the degradation involves as the first step formation of an adduct consisting of the nucleophile and the c/oso-cluster. Afterwards this adduct should react with a protic solvent to give the isolated reaction product. In order to get indications for the expected adduct we studied the attack of nucleophiles in an aprotic solvent. Three types of nucleophiles were studied in this reaction. In the case of the dialkylamide nucleophile best results were achieved from the reaction of the close-cluster with transition metal amides of zirconium and tantalum,17,81 The anionic adduct cluster features a dialkylamide bridging both silicon centres of the silaborane cluster. 

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