Mechanistic Insights of the Initiation Process of the Ring-Opening Polymerization of ε-Caprolactone by Divalent Sm(BH4)2(THF)2 with DFT: Concerted or Oxidative Reaction?

Concerted and oxidative mechanisms for the initiation of the ROP of epsilon-caprolactone by divalent Sm(BH4)(2)(THF)(2) have been computed at the DFT level and compared with experimental data. The concerted polymerization pathway is proposed to occur via divalent [Sm]-(BH4) active species through classical O-acyl cleavage, leading to alpha,omega-dihydroxy telechelic polycaprolactone, which is fully compatible with chain end groups observed for low-M-n samples prepared with Sm(BH4)(2)(THF)(2). Although it is calculated to be favorable, the oxidative route affording radical species is not in accordance with these experimental results, unless one considers transfer reactions with the solvent.