Iron‐Catalysed Hydrofunctionalisation of Alkenes and Alkynes

Abstract

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.

Iron(II)‐Catalyzed Hydrophosphination of Isocyanates

“…When the reaction was performed with nHexNCO,the hydrophosphination competed with the cyclotrimerization reaction, leading to amixture of [nHexNCO] 3 , [9] [Ph 2 PC(=O)N(H)nHex] (3e), and [Ph 2 PC(=O)N(nHex)-C(=O)N(H)nHex] (4e)( Table 1, entries [10][11][12]. For iPrNCO and tBuNCO the temperature was raised to 60 8 8Ct or each reasonable conversions, within 16 hours (entries [15][16][17][18][19], of around 90 %f or 3g and greater than 70 %f or 3h.P revious attempts by others to catalyze the hydrophosphination of tBuNCO with Ph 2 PH were low yielding (< 20 %). For iPrNCO and tBuNCO the temperature was raised to 60 8 8Ct or each reasonable conversions, within 16 hours (entries [15][16][17][18][19], of around 90 %f or 3g and greater than 70 %f or 3h.P revious attempts by others to catalyze the hydrophosphination of tBuNCO with Ph 2 PH were low yielding (< 20 %).…”

Iron(II)‐Catalyzed Hydrophosphination of Isocyanates

“…When the reaction was performed with nHexNCO,the hydrophosphination competed with the cyclotrimerization reaction, leading to amixture of [nHexNCO] 3 , [9] [Ph 2 PC(=O)N(H)nHex] (3e), and [Ph 2 PC(=O)N(nHex)-C(=O)N(H)nHex] (4e)( Table 1, entries 10-12). Meanwhile, reactions with more sterically encumbered secondary and tertiary isocyanates (CyNCO, iPrNCO,a nd tBuNCO) afforded, almost exclusively,t he monoinsertion products (3f-h;entries [13][14][15][16][17][18][19]. For iPrNCO and tBuNCO the temperature was raised to 60 8 8Ct or each reasonable conversions, within 16 hours (entries [15][16][17][18][19], of around 90 %f or 3g and greater than 70 %f or 3h.P revious attempts by others to catalyze the hydrophosphination of tBuNCO with Ph 2 PH were low yielding (< 20 %).…”

“…Meanwhile, reactions with more sterically encumbered secondary and tertiary isocyanates (CyNCO, iPrNCO,a nd tBuNCO) afforded, almost exclusively,t he monoinsertion products (3f-h;entries [13][14][15][16][17][18][19]. For iPrNCO and tBuNCO the temperature was raised to 60 8 8Ct or each reasonable conversions, within 16 hours (entries [15][16][17][18][19], of around 90 %f or 3g and greater than 70 %f or 3h.P revious attempts by others to catalyze the hydrophosphination of tBuNCO with Ph 2 PH were low yielding (< 20 %). [5e] Collectively,t hese results indicate that the observed selectivity between the catalysis of the mono-and diinsertion of isocyanates into Ph 2 PH may be governed by steric factors,p referentially obtaining the diinsertion product for less bulky isocyanates and the monoinsertion product for secondary and tertiary aliphatic isocyanates.…”

Multi‐Step Reactions Involving Iron‐Catalysed Reduction and Hydrogen Borrowing Reactions

“…For this purpose, iron is one of the most abundant transition metals in the Earth's crust, making it one tremendously attractive candidate for catalytic applications due to its low price and toxicity. Thus, since two decades, its use in catalysed transformations has seen an impressive increase, more particularly in the reduction area …”