Fast trigonal/tetragonal interconversion followed by slow chelate-ring closure in the complexation of boronic acids

Relative reactivity of phenylboronic acid to phenylboronate ion toward L-lactate and mandelate at physiological pH

“…Provided that both the chelate-ring closure processes in Eqs. (14) and (15) (both are the ligand substitution processes on the tetrahedral complexes) have the same rate constant, i.e., k 2 ⁎ = k 3 ′ , K 2 k 2 ⁎ N k 3 ⁎ , since K 2 seems to be greater than 1 for the present ligands [12].…”

“…(14)), the fast trigonal/tetragonal interconversion process (K 2 ) is followed by the rate-determining chelate-ring closure process (k 2 ⁎ ), so k 2 = K 2 k 2 ⁎ , whereas in the reaction of boronate ion (Eq. (15)), the rate-determining chelate-ring closure process (k 3 ⁎ ) would be followed by the fast ring-closure process (k 3 ′ ), so k 3 = k 3 ⁎ [12]. Provided that both the chelate-ring closure processes in Eqs.…”

Reaction of boronic acids with tetrafluoroborate? It depends on the acidity

“…6). However, treating methanolic solutions of 4-formylphenylboronic acid (pK a = 7.6) and 4-trifluoromethylphenylboronic acid (pK a = 7.4) [10] with excess TBABF 4 produced no shift in the aromatic proton resonances, indicating that a pK a less than 7.4 is needed for the transfer of fluorides to occur.…”

Direct kinetic measurements for the fast interconversion process between trigonal boronic acid and tetragonal boronate ion at low temperatures

“…Boronic acids (RB(OH) 2 ) are weak acids, of which pK a s are ranging from 7 to 11 depending on the substituent, R [1][2][3][4][5]. Lewis acid-base reaction of boronic acid is expressed as Eq.…”

“…We have estimated the forward rate constant to be in the order of 10 4 M À1 s À1 at À35°C for the reaction in Eq. (2) in acetonitrile, but the precise determination could not be done because of interference by water in the acetonitrile solution [5] HO B OH…”