Why are transition-metal alkyls often unstable? Show β-hydride elimination. Step 1: M–CH₂CH₃ has hydrogens on the β-carbon. Step 2: A β-H transfers to the metal: M–CH₂CH₃ → M–H + CH₂=CH₂. Step 3: The alkene leaves; the alkyl is destroyed. Step 4: Blocking β-H (use CH₃, CH₂Ph, bulky groups) stabilizes alkyls — design principle!