
Tetramethylphosphonium bromide

Tetramethylphosphonium bromide is an organophosphorus compound with the formula (CH3)4PBr. It is a white, water-soluble solid, the salt of the cation tetramethylphosphonium and the bromide anion. It is prepared by treating trimethylphosphine with methyl bromide. 
Reactions.
Deprotonation gives methylenetrimethylphosphine ylide, which can sustain a second deprotonation:
The latter is a precursor to many coordination complexes, e.g., the dicuprous complex Cu2[(Me2P(CH2)2]2.