Lithium Aluminium Hydride and Metallic Iron: A Powerful Team in Alkene and Arene Hydrogenation Catalysis.

Alkenes that normally do not react with LiAlH (3-hexene, cyclohexene, 1-Me-cyclohexene), can be reduced to the corresponding alkanes by a mixture of LiAlH and Fe (the iron was activated by Metal-Vapour-Synthesis). This alkene-to-alkane conversion with a stoichiometric quantity of LiAlH /Fe does not need quenching with water or acids, implying that both H's originate from LiAlH . The LiAlH /Fe combination is also a remarkably potent cooperative catalyst for hydrogenation of multi-substituted alkenes and benzene or toluene. An induction period of circa two hours and the minimally required temperature of 120 °C, suggests that the actual catalyst is a combination of Fe and the decomposition product of LiAlH (LiH and Al ). A thermally pre-activated LiAlH /Fe catalyst did not need an induction time and is also active at room temperature and 1 bar H . A combination of AliBu and Fe is an even more active hydrogenation catalyst. Without pre-activation, tetra-substituted alkenes like Me C=CMe and toluene could be fully hydrogenated.