TY - JOUR
T1 - Role of intramolecular hydrogen bonding in the redox chemistry of hydroxybenzoate-bridged paddlewheel diruthenium(ii,ii) complexes
AU - Kosaka, Wataru
AU - Watanabe, Yudai
AU - Aliyah, Kinanti Hantiyana
AU - Miyasaka, Hitoshi
N1 - Funding Information:
This work was supported by a Grant-in-Aid for Scientific Research (No. 18K05055, 18H05208, 20H00381, 21H01900, 21K18925) from MEXT, Japan, the GIMRT program, the E-IMR project, Tohoku University, Tanaka Kikinzoku Kogyo K. K. W. K. is thankful for the financial support provided by the Iketani Science and Technology Foundation, Grant for Basic Science Research Projects from the Sumitomo Foundation, and the Noguchi Institute.
Funding Information:
This work was supported by a Grant-in-Aid for Scientific Research (No. 18K05055, 18H05208, 20H00381, 21H01900, 21K18925) from MEXT, Japan, the GIMRT program, the E-IMR project, Tohoku University, Tanaka Kikinzoku Kogyo K.K. W. K. is thankful for the financial support provided by the Iketani Science and Technology Foundation, Grant for Basic Science Research Projects from the Sumitomo Foundation, and the Noguchi Institute.
Publisher Copyright:
© The Royal Society of Chemistry 2021.
PY - 2022/1/7
Y1 - 2022/1/7
N2 - The synthesis of a series oftrans-heteroleptic paddlewheel diruthenium(ii,ii) complexes with various hydroxy-substituted benzoate ligands, [Ru2((OH)xPhCO2)2(2,6-(CF3)2PhCO2)2(THF)2] ([RuII,II2]) as tetrahydrofuran (THF) adducts is reported, where (OH)xPhCO2−stands foro-hydroxybenzoate (o-OH),m-hydroxybenzoate (m-OH),p-hydroxybenzoate (p-OH), 2,3-dihydroxybenzoate (2,3-(OH)2), 2,4-dihydroxybenzoate (2,4-(OH)2), 2,5-dihydroxybenzoate (2,5-(OH)2), 2,6-dihydroxybenzoate (2,6-(OH)2), or 3,4-dihydroxybenzoate (3,4-(OH)2), and 2,6-(CF3)2PhCO2−represents 2,6-bis(trifluoromethyl)benzoate. In this heteroleptic series, the redox potential (E1/2) of the [Ru II,II2]/[Ru II,III2]+couple in THF varies over a wide range, from −18 mV (vs.Ag/Ag+) forp-OHto 432 mV for2,6-(OH)2. The redox properties are linearly dependent on the acidity (pKa) of the OH-substituted benzoic acids, but do not depend on the number ofortho-substituted hydroxy (o-OH) groups. This indicates that the steric effect ofo-substituents is irrelevant in the case of hydroxyl groups, owing to the formation of intramolecular hydrogen bonds between theo-OH group and carboxylate oxygens. The value of the Hammett constantσofor theo-OH substituent was determined to be 0.667, indicating a strongly electron-withdrawing character, contrary to the expectation of electron-donating character for an OH group. The redox properties of the compounds were well explained in a framework of Hammett analyses and were also consistent with their HOMO energy levels evaluated by DFT calculations based on the atomic coordinates. The unexpected electron-withdrawing character of theo-OH groups could be attributed to the direct effect of intramolecular hydrogen bonding on the charge density on the carboxylate oxygen.
AB - The synthesis of a series oftrans-heteroleptic paddlewheel diruthenium(ii,ii) complexes with various hydroxy-substituted benzoate ligands, [Ru2((OH)xPhCO2)2(2,6-(CF3)2PhCO2)2(THF)2] ([RuII,II2]) as tetrahydrofuran (THF) adducts is reported, where (OH)xPhCO2−stands foro-hydroxybenzoate (o-OH),m-hydroxybenzoate (m-OH),p-hydroxybenzoate (p-OH), 2,3-dihydroxybenzoate (2,3-(OH)2), 2,4-dihydroxybenzoate (2,4-(OH)2), 2,5-dihydroxybenzoate (2,5-(OH)2), 2,6-dihydroxybenzoate (2,6-(OH)2), or 3,4-dihydroxybenzoate (3,4-(OH)2), and 2,6-(CF3)2PhCO2−represents 2,6-bis(trifluoromethyl)benzoate. In this heteroleptic series, the redox potential (E1/2) of the [Ru II,II2]/[Ru II,III2]+couple in THF varies over a wide range, from −18 mV (vs.Ag/Ag+) forp-OHto 432 mV for2,6-(OH)2. The redox properties are linearly dependent on the acidity (pKa) of the OH-substituted benzoic acids, but do not depend on the number ofortho-substituted hydroxy (o-OH) groups. This indicates that the steric effect ofo-substituents is irrelevant in the case of hydroxyl groups, owing to the formation of intramolecular hydrogen bonds between theo-OH group and carboxylate oxygens. The value of the Hammett constantσofor theo-OH substituent was determined to be 0.667, indicating a strongly electron-withdrawing character, contrary to the expectation of electron-donating character for an OH group. The redox properties of the compounds were well explained in a framework of Hammett analyses and were also consistent with their HOMO energy levels evaluated by DFT calculations based on the atomic coordinates. The unexpected electron-withdrawing character of theo-OH groups could be attributed to the direct effect of intramolecular hydrogen bonding on the charge density on the carboxylate oxygen.
UR - http://www.scopus.com/inward/record.url?scp=85121624070&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85121624070&partnerID=8YFLogxK
U2 - 10.1039/d1dt03791a
DO - 10.1039/d1dt03791a
M3 - Article
AN - SCOPUS:85121624070
VL - 51
SP - 85
EP - 94
JO - Dalton Transactions
JF - Dalton Transactions
SN - 1477-9226
IS - 1
ER -