Transition state search using rPM6: Iron-and manganese-catalyzed oxidation reactions as a test case

Abstract

We present a reparameterization of PM6 (rPM6) for Fe in a similar procedure to that for Mn in our previous work [T. Saito, Y. Takano, Chem. Lett. 2017, 46, 1567]. The performance of the spin unrestricted rPM6 (UrPM6) method has been examined on both energy minimization and transition state (TS) search on the basis of the spin unrestricted density functional theory (UDFT) calculations. For energy minimization, the UrPM6 outperforms the original UPM6 on the basis of the UB3LYP/SVP-optimized geometries. The test set for TS search is comprised of 58 TS structures for oxidation reactions catalyzed by a variety of iron and manganese complexes including active sites of cytochrome P450 and soluble methane monooxygenase as well as their biomimetic complexes. The standard UPM6 method can locate only 21 out of 58 TS structures (36%), whereas an overall success rate is 83% (48 out of 58) by means of UrPM6. Furthermore, the UrPM6- optimized structures can be obtained easily (on the order of several minutes) and 94% of those are found to be utilized for the subsequent refinement by UDFT without any modifications of geometrical parameters.