Phenylmercurypropionate

Phenylmercuric propionate is a more active catalyst for isocyanate-hydroxyl reactions than conventional catalysts. For example, dibutyltin dilaurate, stannous octoate, zinc octoate, triethylenediamine, and N-methyl morpholine, gives polyurethane films and urethane rubber having significantly better properties than those produced using the conventional catalysts.

Probably a poison. When heated to decomposition it emits toxic fumes of Hg. See also MERCURY COMPOUNDS