Activation
of B2pin2 with tBuLi
facilitates the Fe-catalyzed borylation of alkyl, allyl, benzyl, and
aryl halides via the formation of Li[B2pin2(tBu)] (1). The reaction of 1 with
a representative iron phosphine precatalyst generates the unique iron(I)
boryl complex [Fe(Bpin)(dpbz)2] (2).
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.
A bimetallic system consisting of Cu-carbene and Mn-carbonyl co-catalysts was employed for carbonylative C–C coupling of arylboronic esters with alkyl halides, allowing for the convergent synthesis of ketones.
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