Theoretical investigation of different reactivities of Fe(IV)O and Ru(IV)O complexes with the same ligand topology

2016-12-26T10:17:28Z (GMT) by Zhe Tang Yi Wang Peng Zhang
<p>The structures and mechanisms for hydrogen abstraction from isopropylbenzene for four high-valence complexes, <i>cis</i>-β-[Fe<sup>IV</sup>(O)(BQCN)]<sup>2+</sup> (<b>Fe-2b</b> and <b>Fe-2b-2</b>) and <i>cis</i>-β-[Ru<sup>IV</sup>(O)(BQCN)]<sup>2+</sup> (<b>Ru-2b</b> and <b>Ru-2b-2</b>) (BQCN = N,N′-dimethyl-N,N′-bis(8-quinolyl)-cyclohexanediamine), were investigated using density functional theory. Of the two iron complexes, <b>Fe-2b-2</b> has more exposed FeO units than <b>Fe-2b</b>, with iron being further out of the equatorial plane because of the steric interaction of the same ligand topologies with the iron-oxo group <i>trans</i> to a quinolyl or amine nitrogen. The contribution of BQCN to <b>Fe-2b</b> is higher than the contribution to <b>Fe-2b-2</b> as shown by the density-of-states spectra. The iron isomers can abstract hydrogen from isopropylbenzene via two-state reactivity patterns, whereas the ruthenium isomers react with isopropylbenzene via a single-state mechanism. In the gas phase, the relative reactivity exhibits the trend <b>Fe-2b</b> > <b>Fe-2b-2</b>, whereas with the addition of the ZPE correction and the SMD model, the relative reactivity follows <b>Fe-2b-2</b> > <b>Fe-2b</b>. For the ruthenium complexes, the relative reactivity follows the trend <b>Ru-2b-2</b> > <b>Ru-2b</b> in both the gas phase and solvent. Thus, the same ligand topologies with the metal-oxo group <i>trans</i> to a different nitrogen affect the reactivities of the iron and ruthenium complexes.</p>