Expedient Iron-Catalyzed Coupling of Alkyl, Benzyl and Allyl Halides with Arylboronic Esters

While attractive, the iron‐catalyzed coupling of arylboron reagents with alkyl halides typically requires expensive or synthetically challenging diphosphine ligands. Herein, we show that primary and secondary alkyl bromides and chlorides, as well as benzyl and allyl halides, can be coupled with arylboronic esters, activated with alkyllithium reagents, by using very simple iron‐based catalysts. The catalysts used were either adducts of inexpensive and widely available diphosphines or, in a large number of cases, simply [Fe(acac)3] with no added co‐ ligands. In the former case, preliminary mechanistic studies highlight the likely involvement of iron(I)–phosphine intermediates. More irons in the fire: Primary and secondary alkyl, benzyl and allyl halides were coupled with arylboronic esters by using very simple iron‐based catalysts. These were either adducts of inexpensive and widely available diphosphines or, in a large number of cases, simply [Fe(acac)3] with no added co‐ligands (see scheme; acac=acetylacetonate). In the former case, preliminary mechanistic studies highlight the likely involvement of low‐coordinate iron(I)–phosphine intermediates.