If I started with t-butyl bromide react with butylmagneisum bromide, what would be the name of the impurity that could have formed during the preparation of the Grignard reageant. I get 2,2,3,3-tetramethylbutane, I am not sure if it is corrected. Any help is appreciated.

I am not sure of your question. Are you reacting the two alkyl halides with magnesium at the same time? Not the normal technique. Are you reacting t-butyl bromide with n-butylmagnesium bromide? If so why the reference to the preparation of the Grignard reagent. Please explain a little more clearly.