Coordination of Azobisisobutyronitrile with Cobalt Complexes in Cobalt-Mediated Radical Polymerization Disclosed by Linear Correlation between the Equilibrium Constant and Half-Wave Potential

In cobalt-mediated radical polymerization (CMRP) of methyl acrylate with a series of Co(salen) complexes, a linear correlation between the equilibrium constants (K-CMRP) and half-wave potential (E-1/2) was observed. However, this correlation was inconsistent with the simulated trend obtained by density functional theory (DFT) calculations until the axial coordination of azobisisobutyronitrile (AIBN) with organocobalt(III) was added to the model. Control studies using V601, an initiator similar to AIBN with no cyano-group, and tert-butyl cyanide further confirmed that AIBN was the substituent axially coordinating to the organocobalt(III) species. According to the DFT calculation, the function of the coordinated nitrile was mainly to stabilize organocobalt(III), possibly through the formation of an octahedral configuration, rather than to weaken the cobalt-carbon bond through the trans-effect.

Automated summary

In cobalt-mediated radical polymerization (CMRP) of methyl acrylate, a linear correlation between equilibrium constants (K-CMRP) and half-wave potential (E-1/2) was observed, which was inconsistent with theoretical calculations until azobisisobutyronitrile (AIBN) coordination was considered. Experimentally, it was confirmed that AIBN acted as the axial ligand to organocobalt(III). Density functional theory calculations showed that the coordinated nitrile stabilized the organocobalt(III) through the formation of an octahedral configuration.