Theoretical study of the effect of ligand topology on Fe(IV)O and Ru(IV)O complex reactivities

• DFT calculation has determined the influences of the ligand topology on the metal center.
• The Density-of-States spectrums represent that the contribution of BQCN ligand to 3Fe-2b is more than the corresponding contribution to 3Fe-2a.
• The different ligand topologies have little effect on the tunneling effect.
• The ligand topology is an important factor that contributes to the stability and reactivity of non-heme iron complexes, however, it has little effect on the reactivities of the [RuIV(O)(BQCN)]2+ complexes.

Density functional theory calculations were carried out to clarify the effect of ligand topology on the stability and reactivity of cis-α-[FeIV(O)(BQCN)]2+ (Fe-2a), cis-β-[FeIV(O)(BQCN)]2+ (Fe-2b), cis-α-[RuIV(O)(BQCN)]2+ (Ru-2a) and cis-β-[RuIV(O)(BQCN)]2+ (Ru-2b) (BQCN = N,N′-dimethyl-N,N′-bis(8-quinolyl)-cyclohexanediamine). All the iron and ruthenium isomers possess the triplet ground states. The relative stability between the two iron isomers follows the order of Fe-2a > Fe-2b, which is in agreement with the conclusions of Hong et al. Moreover, the trend of the relative stability of the two ruthenium isomers is Ru-2a > Ru-2b. The Density-of-States spectrums represent that the contribution of BQCN ligand to 3Fe-2b is more than the corresponding contribution to 3Fe-2a. The iron isomers react with isopropylbenzene via a two-state reactivity pattern on competing triplet and quintet spin states, while the ruthenium isomers react with isopropylbenzene by a single-state mechanism, only on the triplet spin state. The H-abstraction is affected by the tunneling contribution, which can decrease the reaction barriers. By adding the ZPE correction, PCM model assessed by DFT-D3 (BJ) and the tunneling correction, the analysis of the trend of the hydrogen-abstraction reactions barriers shows that Fe-2a is the more reactive than Fe-2b with the higher FeIV/III redox potential. Moreover, for the ruthenium complexes, although Ru-2a is the more reactive than Ru-2b, only 0.6 kcal/mol lower. Above all, the ligand topology has little effect on the reactivities of the [RuIV(O)(BQCN)]2+ complexes.

The figure offers the contributions of the different ligands to the chemical bonding through the DOS and OPDOS.Figure optionsDownload as PowerPoint slide