TY - JOUR
T1 - Fast trigonal/tetragonal interconversion followed by slow chelate-ring closure in the complexation of boronic acids
AU - Yamamoto, Yoshiaki
AU - Matsumura, Takeshi
AU - Takao, Norihiro
AU - Yamagishi, Hiroaki
AU - Takahashi, Masato
AU - Iwatsuki, Satoshi
AU - Ishihara, Koji
N1 - Funding Information:
Financial Support from the 21COE program “Practical Nano-Chemistry” from MEXT, Japan, and Waseda University Grant for Special Research Projects are gratefully acknowledged.
PY - 2005/8/1
Y1 - 2005/8/1
N2 - Which of the step is rate determining in the complexation of boronic acid with bidentate ligands, the first trigonal/tetragonal interconversion step or the following chelate-ring closure step ? No one could have ever answered this simple question clearly. In this study, we for the first time gave an explicit answer to this question. Reaction systems were devised for kinetic measurements to answer this simple question. At first, pKa values of 15 boronic acids were determined spectrophotometrically at I = 1.0 M and 25 °C: pK a = 6.40 ± 0.06 for 3,5-Cl2PhB(OH)2, 6.62 ± 0.03 for 3,5-(CF3)2PhB(OH)2, 6.95 ± 0.09 for 3,5-Br2PhB(OH)2, 7.04 ± 0.03 for 3-NO2PhB(OH)2, 7.08 ± 0.03 for 3,5-F 2PhB(OH)2, 7.12 ± 0.02 for 2,4-F 2PhB(OH)2, 7.39 ± 0.02 for 4-CF3PhB(OH) 2, 7.50 ± 0.02 for 3-FPhB(OH)2, 7.83 ± 0.02 for 2-FPhB(OH)2, 7.87 ± 0.01 for 3-CF3PhB(OH) 2, 8.11 ± 0.01 for 2-ClPhB(OH)2, 8.14 ± 0.03 for 3-(COOH)PhB(OH)2, 8.15 ± 0.03 for 3-(CH 3CO)Ph(OH)2, 8.20 ± 0.01 for 3-ClPhB(OH) 2, and 8.66 ± 0.05 for 4-FPhB(OH)2. The kinetic results for the reactions of some of these boronic acids with 4-isopropyltropolone clearly show that the rate-determining step is not the interconversion step but the chelate-ring closure step.
AB - Which of the step is rate determining in the complexation of boronic acid with bidentate ligands, the first trigonal/tetragonal interconversion step or the following chelate-ring closure step ? No one could have ever answered this simple question clearly. In this study, we for the first time gave an explicit answer to this question. Reaction systems were devised for kinetic measurements to answer this simple question. At first, pKa values of 15 boronic acids were determined spectrophotometrically at I = 1.0 M and 25 °C: pK a = 6.40 ± 0.06 for 3,5-Cl2PhB(OH)2, 6.62 ± 0.03 for 3,5-(CF3)2PhB(OH)2, 6.95 ± 0.09 for 3,5-Br2PhB(OH)2, 7.04 ± 0.03 for 3-NO2PhB(OH)2, 7.08 ± 0.03 for 3,5-F 2PhB(OH)2, 7.12 ± 0.02 for 2,4-F 2PhB(OH)2, 7.39 ± 0.02 for 4-CF3PhB(OH) 2, 7.50 ± 0.02 for 3-FPhB(OH)2, 7.83 ± 0.02 for 2-FPhB(OH)2, 7.87 ± 0.01 for 3-CF3PhB(OH) 2, 8.11 ± 0.01 for 2-ClPhB(OH)2, 8.14 ± 0.03 for 3-(COOH)PhB(OH)2, 8.15 ± 0.03 for 3-(CH 3CO)Ph(OH)2, 8.20 ± 0.01 for 3-ClPhB(OH) 2, and 8.66 ± 0.05 for 4-FPhB(OH)2. The kinetic results for the reactions of some of these boronic acids with 4-isopropyltropolone clearly show that the rate-determining step is not the interconversion step but the chelate-ring closure step.
KW - Boronic acid
KW - Complexation
KW - Interconversion
KW - Kinetics
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U2 - 10.1016/j.ica.2005.05.026
DO - 10.1016/j.ica.2005.05.026
M3 - Article
AN - SCOPUS:21944433314
SN - 0020-1693
VL - 358
SP - 3355
EP - 3361
JO - Inorganica Chimica Acta
JF - Inorganica Chimica Acta
IS - 12
ER -