In one reaction, a pi-allyl complex containing this element undergoes a Walden inversion in an oxidative addition step that allows a nucleophile to substitute an alkene. Barium sulfate poisons this element (15[1])in a reduction reaction that produces aldehydes. Reducing an acetate with phosphine activates this element in one reaction, and this element is regenerated by copper chloride to catalyze the oxidation of ethylene into acetaldehyde during the (*) Wacker process. This element catalyzes a reaction that forms carbon-carbon bonds with an organoboron (10[1])species and a halide. Heck, Negishi, and (10[1])Suzuki won the 2010 (10[1])Nobel Prize in Chemistry for work on cross-coupling reactions catalyzed by this metal. For 10 points, name this expensive platinum-group metal found in Lindlar’s catalyst, with symbol Pd. ■END■