Relative kinetic reactivity of boronic acid and boronate ion towards Tiron, 2,2′-biphenol, and propylene glycol?

Dalton Transactions Pub Date: 2013-04-26 DOI: 10.1039/C3DT50283J

Abstract

Reaction systems of boronic acid (RB(OH2), R = phenyl or 3-fluorophenyl) with diols and no proton ambiguity were elaborately set up, and kinetic measurements were conducted to elucidate the relative reactivities of RB(OH)2 and RB(OH)3?. In the reactions of phenylboronic and 3-fluorophenylboronic acids with propylene glycol, the reactivity order was: RB(OH)2 >> RB(OH)3?, whereas in the reactions of 3-pyridylboronic acid with Tiron and 2,2′-biphenol, the reactivity of RB(OH)2 was comparable to that of RB(OH)3?. These results are in contrast to those that have been previously reported, and widely accepted for over thirty years, that concluded that the reactivity of RB(OH)3? is several orders of magnitude higher than that of RB(OH)2. The reactivity of Tiron with 3-pyridylboronic acid is affected by the protonation of one of its sulfonate groups.

Graphical abstract: Relative kinetic reactivity of boronic acid and boronate ion towards Tiron, 2,2′-biphenol, and propylene glycol
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