Electronic magnesium compounds

The only magnesium compounds for which structures have been reported that contain electron-deficient bonds are those of dimethyl (123)- and diethylmagnesium (124). The structure common to these two derivatives is XXI, and the data for these compounds along with those from a variety of other organomagnesium derivatives are collected in Table VI for comparison. Clearly, insufficient data are available to draw any specific conclusions concerning the electron-deficient derivatives, but no unexpected deviations appear in the compounds studied. 

Fig. 12. Absorption spectra of the complexes of di-(2-quinolyl)methane with boron and magnesium compounds (R = CeHs) in ether at 20°. A, B, C, and D denote different electronic transitions.

In view of the trend to more controlled and stereoselective reactions with readily available, less expensive and environmentally non-problematic reagents, the light-induced inner-sphere electron transfer between M-C bonds of less polar co-ordinating organometallics (Zn, Al) and the organic substrate seems to be a particularly attractive alternative to thermal reactions from organolithium or -magnesium compounds. 

The metals of group 11 of the periodic table —beryllium, magnesium, calcium, strontium, barium, and radium—are called the alkaline-earth metals. Some of their properties are listed in Table 18-2. These metals are much harder and less reactive than the alkali metals because there are twice as many valence electrons. The compounds of all the alkaline-earth metals are similar in composition they all form oxides MO, hydroxides M(0H)2, carbonates MCO3, sulfates MSO4, and other compounds (M = Be, Mg, Ca, Sr, Ba, or Ra). 

Metal-mediated transformations ofpyridines are thus mainly the realm of main group highly electron-rich compounds such as alkyl derivatives of Uthium, magnesium and zinc, aluminum hydrides, etc. This chemistry will be very succincdy covered with an emphasis on recent developments, as it will the related alkyl migration to pyridines which have been found in a number of f-block derivatives, a topic which has been recently reviewed. In particular, rollover cyclometalations, which are important processes that can be operative in bipy complexes, will not be mentioned, and the interested reader is referred to a recent account of this chemistry. 

An example of the physical impregnation method is provided by U.S. Patent 4,302,565, which was discussed above. The dissolution of a magnesium compound and a titanium compound in a suitable solvent, usually an electron donor solvent such as tetrahydrofuran (THF), can lead to the formation of a new species (catalyst precursor) that provides a highly-active Ziegler system when activated. Removing the solvent at elevated temperatures in the presence of a support material such as silica will precipitate the precursor into the pores of the silica. In this method it is necessary that... 

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