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.
Deprotonation gives methylenetrimethylphosphine ylide, which can sustain a second deprotonation:[1]
(CH3)4PBr + BuLi → CH3)3P=CH2 + LiBr + BuH
CH3)3P=CH2 + BuLi → CH3)2P(CH2)2Li + BuHThe latter is a precursor to many coordination complexes, e.g., the dicuprous complex Cu2[(Me<sub>2</sub>P(CH<sub>2</sub>)<sub>2</sub>]2.[2]