Nonsolvated Grignard reagents

However, microscale (matrix isolation spectroscopic) experiments show that the nonsolvated Grignard reagent forms at even lower temperatures (15 K), and no intermediate charge-transfer complex is formed ... 

The initial black matrix in the macroscale experiments is explained by the presence of dark-colored Mg2, Mgs, (Mg) t species, and these react at warm-up, but Mg atoms react immediately upon codeposition. The reactivity of the nonsolvated Grignard reagents is different from the analogous solvated speciese.g., the nonsolvated species abstract hydrogen from acetone rather than adding to the carbonyl group, and crotonaldehyde adds 1,2- rather than 1,4- as with solvated systems. 

A simple synthetic route to compounds of the type R Mg(NR R ) is the reaction of equimolar amounts of MgR and a secondary amine, HNR R . By this method sterically hindered 1,3,6,8-tetra-t-butylcarbazole and diethylmagnesium in THF afford 52 as the bistetrahydrofuran adduct, and hexamethyldisilazane (HN(TMS)2) and "BuMg Bu in heptane form nonsolvated 53 [23]. Metalation of activated G-H groups by the amide bases Mg(TMP)2 (TMPH = 2,2,6,6-tetramethylpiperidine) or Mg(N Pr2)2 can also produce organomagnesium amides. Reactions of metal amide (MNR R (M = Li or Na)) with the appropriate Grignard reagent have been used to produce 54 [24] and 55 [25] (Scheme 3.31). 

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