This reaction superseded the Castro–Stephens reaction by removing the need for copper as a catalyst for the cross-coupling step. For 10 points each:
[10h] Name this cross-coupling reaction used to couple aryl or vinyl halides to alkynes.
ANSWER: Sonogashira cross-coupling
[10m] The Sonogashira coupling is catalyzed by copper and this incredibly expensive metal, which also catalyzes the Heck, Stille, and Suzuki couplings.
ANSWER: palladium [or Pd]
[10e] The catalytic cycle for palladium cycles between its oxidation state of this number and its plus-two state. This is the charge of a neutral atom.
ANSWER: zero [accept +0]
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