Anthracene complex with magnesium

Highly reactive calcium can be readily prepared by the reduction of calcium halides in tetrahydrofuran solution with preformed lithium biphenylide under an argon atmosphere at room temperature.5 This colored calcium species seems to be reasonably soluble in THF. However, the reactive calcium complex prepared from preformed lithium naphthalenide was insoluble in THF solution and precipitated out of solution to give a highly reactive black solid. The exact nature of this black calcium complex has not been determined. Acid hydrolysis of the black material releases naphthalene as well as THF. Accordingly, the most likely structure of the black material is a Ca-naphthalene-THF complex similar in nature to the soluble magnesium-anthracene complex recently reported.6... 

In the Rieke process for the reduction of salts, magnesium is suitable only in exceptional cases as a substitute for potassium. However, the ready formation of the anthracene complex 1 can also be exploited for this purpose. As shown in Scheme 3. not only activated metals can be generated by a catalytic cycle, but also, in the presence of suitable ligands, complexes with a zero- or low-valent central atom, such as [M(cod)2] (M = Ni, Pt), [CP2M] (M = V, Co, Fe), and [Pd(PPh3)3], and [Mo(butadiene)3] can be prepared [45]. 

A secondary reaction has been identified in the reaction of magnesium-trimethylsilyl substituted anthracene complexes w ith benzylic halides, which is the addition of preformed Grignard reagent with the generated anthracene, equation (8.5) [44]. However, this is slow enough not to be a serious problem. The addition is favoured by the electron-withdrawing silyl substituents otherwise more forcing conditions are required [49]. 

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