Amides of the Group 13 Metals

This survey is confined to an overview of group 13 amides containing M-NR2 (R = H, alkyl, aryl, silyl, etc.) groups derivatives where nitrogen is part of a delocalized or polydentate ligand, are not generally covered. However, as in the 1980 book, iminome-tallanes (metal imides) of formula (RMNR ) are treated because of their close relationship to amides and also because of the relevance of the lower derivatives (n= 1, 2 or 3) for possible M N multiple bonding. 

Metal Amide Chemistry Michael Lappert. Andrey Protchenko, Philip Power and Alexandra Seeber 

There are three major synthetic routes to group 13 metal amides as exemplified by reactions of Equations (8.1-8.3) (M = Al-Tl, X = halogen, M = Li, Na or K). 

The simple, salt elimination reaction of Equation (8.1) has been employed for amides of all the group 13 metals. In addition, it is currently the only well-established route to M(I) metal amides where M = Ga or Tl. The alkane elimination route of eqn. (8.2) is generally employed only for M = Al or Ga. This synthetic approach is also used for the metal imides (RMNR )n where a primary amine H2NR is the reactant. The use of metal hydrides, of which Equation (8.3) is but one example, is limited mainly to aluminium and, to a lesser extent, gallium because of the decreased stability of the heavier metal hydrides. 

Several other synthetic approaches, for example (i) transamination, (ii) the direct reaction between a primary or a secondary amine with a metal(III) halide, or (iii) the direct reaction of a metal (e.g. aluminium) and an amine in the presence or absence of hydrogen, as well as a number of other approaches (outlined in Chapter 4 of Ref. 1) have been known for many years and are occasionally employed. The procedure (iii), in particular, has been used for matrix isolation smdies of the simplest group 13 metal amides (see below). However, it is the three general approaches of Equations (8.1-8.3) that are by far the most commonly used. 

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Molecular structure elucidation, principally by single crystal X-ray diffraction, has become almost routine and is now available for the majority of the metal amides presently discussed. In the 1980 book, however, such data were provided for just 112 compounds, 54 of which were for d- and/-block metals and 41 for the Group 13 metal amides. The contrast with the developing situation is illustrated by reference to Group 1 metal amides from four X-ray data sets in 1980 there were more than 200 by the end of 2007. 

A similar effect of metal-induced conversion of a calixarene conformation with intramolecularly bound amide groups (closed form unable to bind guest molecules) into a conformation with more separated unbound amide groups (open form) capable of complexation with amide guests operates in the allosteric regulation of the host 13 (Fig.A). ... 

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