The metal-catalysed hydrofunctionalisation of alkenes and alkynes provides a convenient and atom-economic route to diversely functionalised products with control of regio-, chemo- and stereoselectivity. As one of the most abundant elements on earth, iron offers a level of sustainable and long-term availability that is uncommon for most transition metals. Although iron is commonly found in the oxidation states of +2 and +3, the use of redox-active ligands has allowed the synthesis and application of low oxidation state iron complexes in catalysis. A broad range of hydrofunctionalisation reactions have been developed by using iron catalysts in a wide variety of oxidation states. Intense development over the past decade has resulted in the development of iron-catalysed hydroamination, hydroalkoxylation, hydrocarboxylation, hydrothiolation, hydrovinylation, hydrosilylation, hydroboration, hydrophosphination, hydromagnesiation and carbonylation reactions, amongst others. With the field still in its infancy, there is great potential for further developments in the mechanistic understanding and synthetic and industrial applicability of these processes.

The iron-catalysed reduction of olefins has been achieved using a simple iron salt and sodium triethylborohydride. A wide range of mono- and trans-1,2-disubstituted alkenes have been reduced (91–100%) using 25 mol% iron(II) triflate, 1 mol% N-methyl-2-pyrrolidinone and 4 equivalents of sodium triethylborohydride. The reduction of alkynes to alkanes is also reported (up to 84%). Significantly, the reduction of trisubstituted alkenes has also been achieved (60–86%).