Cross-Coupling in Practice: Choosing Ligand, Base and Conditions · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Making couplings work

Science · Chemistry · ages 22-24
Name ______________________   Date ____________

  1. Which pair plus palladium calls for a Suzuki coupling?

    • Aryl boronic acid with aryl bromide
    • Two alkanes with no functional groups
    • An alcohol with a ketone

  2. What does ligand bulk do to reductive elimination?

    • It squeezes the partners together so it fires
    • It stops it completely
    • It has no effect on it

  3. A defined precatalyst releases the active species faster than a flask mix of metal and ligand.

    Circle one:   True   False

  4. Oxidative addition is fast but product barely forms. Which step should the next change target?

    • Oxidative addition again
    • Reductive elimination
    • Weighing the reagents

  5. An aryl chloride fails and returns starting material. Which change aims at the fault?

    • Less catalyst overall
    • A colder reaction
    • A bulkier electron-rich phosphine

  6. A flask mix of metal and ligand gives a sleepy reaction. Why would a defined precatalyst help?

    • It adds extra unrelated metals
    • It removes the need for a base
    • It guarantees exact ratio and fast release of the active species

  7. Two fixes are proposed for a stalled chloride: bulkier ligand or stronger base. How do you argue between them?

    • Pick randomly, both do the same job
    • Ask which slow step each targets and match it to the diagnosis
    • Always pick the base, it is cheaper

  8. A student answers every failure with a stronger base. When is that the wrong instinct?

    • When the base is already strong
    • When recovered starting material shows oxidative addition never ran
    • When the solvent is polar
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Making couplings work W1-mt_y2vF6EDb2X-s1

  1. Aryl boronic acid with aryl bromide · Suzuki is built for the boronic acid partner.
  2. It squeezes the partners together so it fires · Crowding at the metal pushes the two partners into one bond.
  3. True · The fixed ratio avoids idle metal waiting for ligand.
  4. Reductive elimination · A late stall points downstream at reductive elimination.
  5. A bulkier electron-rich phosphine · Recovered start means oxidative addition stalled, which richness and bulk fix.
  6. It guarantees exact ratio and fast release of the active species · Much of the flask-mix metal never becomes active.
  7. Ask which slow step each targets and match it to the diagnosis · Each variable fixes its own step, so the diagnosis picks the fix.
  8. When recovered starting material shows oxidative addition never ran · Base cannot fix a step that needs ligand richness instead.
Worksheet · LightMySky