Alkali metal hydrocarbyls

Although trimers are quite rare, a more preferred type of supramolecular association in solvated alkali metal hydrocarbyls is the formation of tetramers in the solid state. Typical examples of cyclic tetramers are the sodium o-xylyl derivative [Na(o-xylyl)(tmeda)]4, 41, and the diphenylmethyl complex [NaCHPh2(tmeda)]4, 42 [41], The tetrameric THF adduct of -butylethynyllithium, 35, forms a heterocubane... 

Little information has been published on the molecular structures and self-assembly of the higher homologs of the alkali metal hydrocarbyls, i.e. for example... 

Crystallization in the presence of tmeda affords a tetrameric aggregate of composition [(tmeda)NaCH2C6H2Me2(OLi)]4, 205 [178]. A distorted U4O4 cube forms the central part of the molecule. Both the lithium and sodium atoms act as bridges between the methylene units and the oxygen atoms. The compound can be regarded as a model intermolecular superbase and overcomes the problem of differing solubilities of lithium alkoxides and the heavier alkali metal hydrocarbyls. 

Of great importance as precatalysts in organolanthanide-catalyzed processes are lanthanide hydrocarbyls containing the bulky bis(trimethylsilyl)methyl ligand. They are also the most suitable precursors for the preparation of the dimeric hydrides [(C5Me5)2Ln(/t-H)]2. Such compounds can be isolated completely free of coordinating solvents and alkali metal halides Eq. (2) [19-25. ... 

The structures of base-free hydrocarbyls of the alkali metals have been investigated much less than those of the solvated species [4], The first example of an unsolvated dimer was [LiC(SiMe3)3]2,1 [5]. This pyrophoric compound was prepared by reacting the corresponding HgBr derivative with n-butylhthium. 

Yet another type of hydrocarbyl bridging has been established for some solvated triphenylmethyl derivatives of the heavier alkali metals. [NaCPh3(tmeda)] , 64, and [KCPh3(diglyme)] , 66 [57], are supramolecularly associated into zigzag chains by weak intermolecular sodium-carbon contacts. 

Electropositive elements, the alkali and alkaline earth metals, react directly with hydrocarbyl substituted / -diketones to provide the corresponding metal chelates. The methine protons in perfluoroalkyl-substituted diketones are more acidic so that, in these cases, the method is applicable to other metals such as Fe, In, Ga, Mn, Pb, V and Sc.140,141 Electrochemical syntheses of M(Me-COCHCOMe)2 (M = Fe, Co, Ni) using the appropriate metal anode have been described142 and the method should be widely applicable. 

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