Magnesium compounds dicyclopentadienyls

The dicyclopentadienyl derivatives of these elements which are known at the present time (those of magnesium and calcium) are in many respects similar to those of the alkali metals, being colorless, saltlike compounds. The magnesium compound was successfully prepared by the interaction of sodium cyclopentadienyl and magnesium bromide in tetra-hydrofuran 214), by thermal decomposition of cyclopentadienyl magnesium bromide 214) and, recently, by the action of cyclopentadiene... 

Wilkinson et al. 196) were the first to discover C5H5 ligand transfer from one transition metal to another. Thus a number of cyclopentadienyl compounds react with FeCl2 to give ferrocene. This is an important criterion for some ionic character in the metal-cyclopentadienyl bond. Only in solutions of the alkali metal cyclopentadienides is there a noticeable concentration of CjHj- ions 197). It is questionable whether even the so-called ionic magnesium and manganese dicyclopentadienyls produce CjHj" ions in solution 198). Thus it may be assumed that in all cases investigated... 

Stannous chloride reacts with cyclopentadienyl lithium in dimethyl-formamide to give the compound Sn(C6H6)2 48). This substance is unstable in air, forms colorless crystals (mp 105°), and is moderately soluble in benzene, ether, and petroleum ether. Cold water does not effect hydrolysis, but acids bring about decomposition with liberation of cyclopentadiene. The interaction of aryl tin (IV) chlorides and cyclopentadienyl magnesium bromide leads to a series of dicyclopentadienyl-tin(IV) aryl compounds 93) which are unstable in air or in light and are rapidly hydrolyzed by water. 

The first allyl derivative of a rare earth was the complex dicyclopentadienyl allyl scandium, prepared by Coutts and Wailes (1970) from dicyclopentadienyl scandium chloride and allyl magnesium chloride in benzene-tetrahydrofuran. The orange compound shows an NMR spectrum with a singlet for the cyclopentadienyl protons at 5.90 ppm, and a quintet at 7.29 and a doublet at 3.05 ppm for the fluxional allyl group. The fluxional allyl group is also implicated by the IR band at 1475 cm for a delocalized C—C stretching vibration. 

The first approach to the synthesis of actinide tetracyclopentadienyls, Cp4Th (Fischer and Tribner 1962) and CP4U (Fischer and Hristidu 1962), was made by reacting the actinide tetrachlorides and KCp in benzene. These compounds, due to their low solubility, required purification by Soxhlet extraction. Some other alternative synthetic approaches to tetracyclopentadienyl derivatives included the reaction of the metal tetrafluorides with dicyclopentadienyl magnesium in the absence of solvent (Reid and Wailes 1966) and, in the case of M = U, the reaction of uranium tetradiethylamide and freshly distilled cyclopentadiene (Paolucci et al. 1985a) ... 

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