Grignard reagent synthesis?

Using solid Magnesium (Mg), anhydrous diethyl ether, and t-butyl bromide, what would be the structure and name of the “impurity” that could have formed during the preparation of the Grignard reagent.

My answer is that it is butyl magnesium bromide. However it states “impurities”, is what I said the impurity or is it something else that I missed.

UBC Chem 235? LOL

If you are….I think butylmagnesium bromide is the Grignard (as stated in the second question). The impurity is the reaction of the grignard w/ t-butyl bromide.

For example, in the experiment, the grignard reagent, phenylmagnesium bromide + bromobenzene —> Biphenyl + MgBr2 (this was equation #5 written on the board in the lab).

So for this question:
butylmagnesium bromide + t-butyl bromide —> 2,2,3,3-tetramethylbutane + MgBr2