Alkyls of B subgroup metals

The IIB alkyls are normal covalent compounds, the chemical reactivity of which decreases from that of the violently reactive Zn(CH3)2 through Cd(CH3)2 to the relatively inert Hg(CH3)2. The high resolution Raman spectra of these compounds show that the molecules are linear the bond lengths are respectively 1-93,2-11, and 2-09 

The alkyls of Na, K, Rb, and Cs are colourless amorphous solids which are insoluble in all solvents except the liquid zinc dialkyls, with which they react to form compounds such as NaZn(C2Hs)3. The Li compounds are quite different, for they are soluble to varying extents in solvents such as benzene, in which they are polymeric, and both lithium methyl and ethyl exist as colourless crystalline solids at ordinary temperatures. 

Group II provides the crystalline Be(CH3)2, the very reactive magnesium dialkyls, and compounds of the alkaline-earths such as the dimethyls of Ca, Sr, and Ba.( ) 

A number of aluminium alkyls have been prepared A1(CH3)3 by refluxing A1 with CH3I in a nitrogen atmosphere, and the ethyl, n- and iso-propyl compounds by heating A1 with the appropriate mercury dialkyl at 110°C for 30 hours. At ordinary temperatures they are water-white liquids (the trimethyl melts at 15°C), very reactive and spontaneously inflammable in air. The trimethyl is dimeric in benzene solution and in the vapour state, the ethyl and n-propyl dimers show 

Since the structures of the compounds of the heavier alkali metals and of the alkaline-earths are not known our discussion is restricted to the alkyls of li. Be, Mg, and Al. All are electron-deficient compounds in which some or all of the CH3 groups form two or three bonds to metal atoms. These are described as 3- or 4-centre bonds formed by overlap of an sp orbital of C with appropriate orbitals of the metal atoms. 

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