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:
 * (CH3)4PBr +  BuLi →  CH3)3P=CH2  +  LiBr  +  BuH
 * CH3)3P=CH2 +  BuLi →  CH3)2P(CH2)2Li  +  BuH

The latter is a precursor to many coordination complexes, e.g., the dicuprous complex Cu2[(Me2P(CH2)2]2.