Design of a catalyst through Fe doping of the boron cage BH for CO hydrogenation and investigation of the catalytic character of iron hydride (Fe-H).

The innovative catalyst Fe@BH is designed through Fe doping of the boron cage BH and is employed to catalyze CO hydrogenation using a quantum mechanical method. First, the structure of the Fe@BH complex is characterized through calculated B NMR chemical shifts and Raman spectra, and the interactions between Fe and the four H atoms of the opening in the cage are analyzed, which show that various iron hydride (Fe-H) characteristics exist. Subsequently, the potential of Fe@BH as a catalyst for the hydrogenative reduction of CO in the gas phase is computationally evaluated. We find that an equivalent of Fe@BH can consecutively reduce double CO to obtain the double product HCOOH through a two-step reduction, and Fe@BH and Fe@BH are successively obtained. The Fe presents single-atom character in the reduction of CO, which is different from the common iron(ii) catalyzed CO reduction. The calculated total free energy barrier of the first CO reduction is only 8.79 kcal mol, and that of the second CO reduction is 25.71 kcal mol. Every reduction reaction undergoes two key transition states TSC-H and TSO-H. Moreover, the transition state of the C-H bond formation TSC-H is the rate-determining step, where the interaction between π* and the weak σ bond plays an important role. Furthermore, the hydrogenations of Fe@BH and Fe@BH are investigated, which aim at determining the ability of Fe-H circulation in the Fe doped decaborane complex. We find that the hydrogenation of Fe@BH undergoes a one-step H-adsorbed transition state TSH-adsorb with an energy barrier of 6.42 kcal mol from Fe@BH. Comparing with the hydrogenation of Fe@BH, it is slightly more difficult for the hydrogenation of Fe@BH, where the rate-determining step is the H-cleaved transition state TS2H-H with an energy barrier of 17.38 kcal mol.