ABSTRACT
The highly active mixed-ligand catalytic system NiCl2(dppp)/dppf combined with the reducing effect of zerovalent Zn and of other metals was used to demonstrate a method for the dramatic acceleration of the rate and for the enhancement of the yield of Ni-catalyzed neopentylglycolborylation of aryl halides. A diversity of electron-rich and electron-deficient aryl iodides, bromides, and chlorides were efficiently neopentylglycolborylated, typically in 1 h or less. This acceleration is particularly remarkable for the generally less reactive aryl bromides and chlorides and for all ortho-substituted aryl halides. By accelerating the rate of borylation and reducing its reaction time to complete conversion, pathways leading to protodeborylated or hydrodehalogenated side products have a reduced impact on the outcome of the overall reaction. Although Zn powder was the reducing agent of choice, compatibility of this technique with more readily recoverable Zn chips, as well as other metals such as Mn, Mg, Fe, Al, and Ca, has demonstrated the broad scope of this synthetic method.
Subject(s)
Boranes/chemistry , Hydrocarbons, Halogenated/chemistry , Metals/chemistry , Nickel/chemistry , Catalysis , Ligands , Molecular StructureABSTRACT
The mixed-ligand system NiCl(2)(dppp)/dppf is shown to be an effective catalyst for the neopentylglycolborylation of ortho-, meta-, and para-substituted electron-rich and electron-deficient aryl mesylates and tosylates. The addition of Zn powder as a reductant dramatically increases the reaction yield and reduces the reaction time by more than an order of magnitude, providing complete conversion in 1-3 h.
