Optical Resolution of Carboxylic Acid Derivatives of Homoleptic Cyclometalated Iridium(III) Complexes via Diastereomers Formed with Chiral Auxiliaries

Azusa Kanbe; Kenta Yokoi; Yasuyuki Yamada; Makoto Tsurui; Yuichi Kitagawa; Yasuchika Hasegawa; Daiji Ogata; Junpei Yuasa; Shin Aoki

doi:10.1021/acs.inorgchem.3c00685

Optical Resolution of Carboxylic Acid Derivatives of Homoleptic Cyclometalated Iridium(III) Complexes via Diastereomers Formed with Chiral Auxiliaries

Inorg Chem. 2023 Jul 24;62(29):11325-11341. doi: 10.1021/acs.inorgchem.3c00685. Epub 2023 Jul 11.

Authors

Azusa Kanbe¹, Kenta Yokoi¹, Yasuyuki Yamada^{2

3

4}, Makoto Tsurui⁵, Yuichi Kitagawa^{6

7}, Yasuchika Hasegawa^{6

7}, Daiji Ogata⁸, Junpei Yuasa⁸, Shin Aoki^{1

9

10}

Affiliations

¹ Faculty of Pharmaceutical Science, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
² Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
³ Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
⁴ JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
⁵ Graduate School of Chemical Sciences and Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
⁶ Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-Ku, Sapporo, Hokkaido 060-8628, Japan.
⁷ Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University, Kita-21, Nishi-10, Kita-Ku, Sapporo, Hokkaido 001-0021, Japan.
⁸ Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
⁹ Research Institute for Science and Technology (RIST), Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
¹⁰ Research Institute for Biomedical Science (RIBS), Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.

Abstract

We report on a facile method for the optical resolution of cyclometalated iridium(III) (Ir(III)) complexes via diastereomers formed with chiral auxiliaries. The racemic carboxylic acids of Ir(III) complexes (fac-4 (fac-Ir(ppyCO₂H)₃ (ppy: 2-phenylpyridine)), fac-6 (fac-Ir(tpyCO₂H)₃ (tpy: 2-(4'-tolyl)pyridine)), and fac-13 (fac-Ir(mpiqCO₂H)₃ (mpiq: 1-(4'-methylphenyl)isoquinoline))) were converted into the diastereomers, Δ- and Λ-forms of fac-9 (from fac-6), fac-10 (from fac-4), fac-11 (from fac-6), and fac-14 (from fac-13), respectively, by the condensation with (1R,2R)-1,2-diaminocyclohexane or (1R,2R)-2-aminocyclohexanol. The resulting diastereomers were separated by HPLC (with a nonchiral column) or silica gel column chromatography, and their absolute stereochemistry was determined by X-ray single-crystal structure analysis and CD (circular dichroism) spectra. Spectra of all diastereomers of the Ir(III) complexes are reported. Hydrolysis of the ester moieties of Δ- and Λ-forms of fac-10, fac-11, and fac-14 gave both enantiomers of the corresponding carboxylic acid derivatives in the optically pure forms, Δ-fac and Λ-fac-4, -6, and -13, respectively.