Tetramethylphosphonium bromide

File:((Me2P(CH2)2)Cu)2.png|thumb|left|144px|Structure of Cu2[(Me2P(CH2)2]2. 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. ==References==