Mechanochemical reactions may generate products that are distinctly different from those obtained in solution. Often the difference is ascribed to the special conditions present during grinding or milling; e.g., the cracking of crystals and the generation of large static electric fields. A less commonly considered source of the difference, at least for organometallic synthesis, is the removal of reaction barriers associated with the use of ethereal solvents (e.g., THF, Et2O, DME). Thus as expected for a typical halide metathesis, the reaction of Cp2TiCl2 with 2 equiv K(O-tBu) in THF simply yields Cp2Ti(O-tBu)2 (Organometallics, 1984, 3, 223). If the same ratio of reagents is ground without solvent, however, the major product is the monocyclopentadienyl complex CpTi(O-tBu)3, despite the stoichiometric imbalance of reagents. Unexpectedly, if the 1:2 reaction of Cp2TiCl2 and K(O-tBu) is performed in hexanes, CpTi(O-tBu)3 is also formed, but in a 1:1 ratio with Cp2Ti(O-tBu)2. Clearly, the ring displacement observed under mechanochemical conditions or in a nonpolar solution environment is suppressed in THF. The significance of this effect in interpreting mechanochemical reaction pathways will be discussed.

Synthesis in nonpolar solvents: An unexpected mechanochemical parallel

251st National Meeting (2016)

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