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

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