Iron-containing complex hydrides are a fascinating class of materials for hydrogen storage applications because they consist of abundant iron and usually contains [FeH6](4-) complexes, resulting in high hydrogen densities. In this study, we synthesized theoretically predicted Li3AlFeH8, which has the highest gravimetric hydrogen density of all transition metal complex hydrides, through a hydrogenation reaction of LiH, AlH3, and pure iron powder mixture under high pressure. The reaction process was observed in situ using a synchrotron radiation x-ray diffraction technique to clarify its reaction kinetics. The reaction temperature and pressure were changed to optimize reaction conditions for obtaining single phase Li3AlFeH8. Unfortunately, we did not obtain single phase Li3AlFeH8 because the reaction was slow. In addition, there were other phases with similar thermodynamic stabilities to that of Li3AlFeH8. Another novel hydride, LiAlFeH6, was found to be synthesized above 850 degrees C at 9 GPa. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.