Tetraethylborate as an ethyl transfer reagent

Article abstract of DOI:10.1021/om00156a028

Reaction of NaBEt₄ with RhCl(C₂H₄)(triphos) (I), where triphos is MeC(CH₂PPh₂)₃, gives RhH-(C₂H₄)(triphos). Coordinated ¹³C₂H₄ in labeled I is liberated during the reaction, proving that NaBEt₄ is the source of the ethylene coordinated in the product. Compound I reacts at 1 atm and 25°C with ¹³C₂H₄ or H₂ to give RhCl(¹³C₂H₄)(triphos) or Rh(H)₂Cl(triphos), respectively. It is proposed that all three reactions proceed by a mechanism in which one arm of the triphos ligand in I dissociates to yield a planar RhCl-(C₂H₄)(η²-triphos) transient. Both five-coordinate species RhX(C₂H₄)(triphos) (X = H, Cl) are unusual in showing relatively high barriers for both phosphorus site exchange and olefin rotation. In contrast to the reaction of I with NaBEt₄, the reaction with NaBPh₄ stops at Rh(η²-triphos) (η⁶-PhBPh₃) and shows no further conversion to RhPh(C₂H₄)(triphos).