Triphenylphosphine oxide is a phosphine ligand used for coupling reactions, epoxidations, and michael reactions. TPPO is also used to induce crystallization of otherwise difficult to crystallize compounds.A phosphine ligand used for coupling reactions, epoxidations, and Michael reactions Triphenylphosphine oxide is a phosphine ligand used for coupling reactions, epoxidations, and michael reactions. TPPO is also used to induce crystallization of otherwise difficult to crystallize compounds. A phosphine ligand used for coupling reactions, epoxidations, and Michael reactions