Photoactive,octahedral transition metal complexes supported by rigid,multidentate ligand scaffolds have been successfully deployed for diverse photochemical processes.Challenges remain,however,in addressing deficienci...Photoactive,octahedral transition metal complexes supported by rigid,multidentate ligand scaffolds have been successfully deployed for diverse photochemical processes.Challenges remain,however,in addressing deficiencies in reaction scalability,selectivity,and media penetration.In this regard,the development of new materials with intense red or near-infrared(NIR)absorption is of great interest.Herein,we report the synthesis,structure,and spectroscopic characterization of air-stable,dicationic transition metal complexes[M(CNC)_(2)]^(2+)(M=Cr,Mn,and Fe)supported by bis(carbene)-amide CNC pincer ligands.Results show intense NIR absorption(ε_(max)≈10000 M^(−1) cm^(-1))with the metal-dependent peak maxima spanning the first and second NIR regions.Importantly,the lowest energy main NIR absorption in each complex is assigned to the ligand-to-metal charge-transfer(LMCT)transition from the amide-based non-bonding orbital to the three-centered N–M–Nπ-antibonding orbital.Broadly,our studies provide a blueprint for the design of intense NIR-absorbing metal complexes based on a parallel N–M–Nπ-bonding motif with flanking strong field carbene donors.展开更多
Hydrogen atom transfer (HAT) reactions of metal–oxygen intermediates such as metal-oxo, -hydroxo and -superoxo species have so far been studied extensively. However, HAT reactions of metal-aqua complexes are yet to b...Hydrogen atom transfer (HAT) reactions of metal–oxygen intermediates such as metal-oxo, -hydroxo and -superoxo species have so far been studied extensively. However, HAT reactions of metal-aqua complexes are yet to be studied in comparison with those of the corresponding metal-hydroxo complexes. In this study, a series of Mn(Ⅲ)-aqua complexes, [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) (dpaq^(5R) = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate with a substituent at the 5-position;R = NO_(2), Cl, H, Me and OMe) were synthesized by protonating the corresponding Mn(Ⅲ)-hydroxo complexes, [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+), with trifluoromethanesulfonic acid (HOTf). X-ray crystal structures of both [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+) and [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) complexes showed a mononuclear Mn^(Ⅲ) center in a distorted octahedral environment. The electronic substitution effect of the dpaq ligand on the HAT reactions of [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+) and [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) was then examined by determining the rate constants (k2) of the HAT reactions from 4-methoxy-2,6-di-tert-butylphenol to the Mn(Ⅲ)-hydroxo and -aqua complexes. Hammett plots indicate that HAT from 4-methoxy-2,6-di-tert-butylphenol to [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+) proceeds via an oxidative asynchronous coupled proton–electron transfer (CPET), whereas HAT from 4-methoxy-2,6-di-tert-butylphenol to [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) proceeds mainly via a basic asynchronous CPET. The contribution of a stepwise electron transfer (ET)/proton transfer (PT) pathway is discussed by comparing the electronic substitution effect on the rate constants of outer-sphere electron transfer and HAT reactions. This study has provided valuable insights into the asynchronous CPET mechanisms of HAT reactions in which the oxidative vs. basic pathways are determined to exhibit reversed electronic substitution effects on HAT reactions of Mn(Ⅲ)-hydroxo and Mn(Ⅲ)-aqua complexes.展开更多
基金supported by the National Research Foundation of Korea(2022M3C1A3092056 to Y.L.and RS-2025-02634479 to S.L.)Seoul National University(Mid-Career Bridging Program to Y.L.and Ascending SNU Future Leader Fellowship to S.L.).
文摘Photoactive,octahedral transition metal complexes supported by rigid,multidentate ligand scaffolds have been successfully deployed for diverse photochemical processes.Challenges remain,however,in addressing deficiencies in reaction scalability,selectivity,and media penetration.In this regard,the development of new materials with intense red or near-infrared(NIR)absorption is of great interest.Herein,we report the synthesis,structure,and spectroscopic characterization of air-stable,dicationic transition metal complexes[M(CNC)_(2)]^(2+)(M=Cr,Mn,and Fe)supported by bis(carbene)-amide CNC pincer ligands.Results show intense NIR absorption(ε_(max)≈10000 M^(−1) cm^(-1))with the metal-dependent peak maxima spanning the first and second NIR regions.Importantly,the lowest energy main NIR absorption in each complex is assigned to the ligand-to-metal charge-transfer(LMCT)transition from the amide-based non-bonding orbital to the three-centered N–M–Nπ-antibonding orbital.Broadly,our studies provide a blueprint for the design of intense NIR-absorbing metal complexes based on a parallel N–M–Nπ-bonding motif with flanking strong field carbene donors.
基金supported by the NRF of Korea through CRI(NRF-2021R1A3B1076539 to W.N.)the Basic Science Research Program(NRF-2020R1I1A1A01074630 to Y.-M.L.and NRF-2019R1I1A1A01055822 to M.S.S.)+1 种基金supported by Grants-in-Aid(no.16H02268 to S.F.)from the Ministry of Education,Culture,Sports,Science and Technology(MEXT)Japan.
文摘Hydrogen atom transfer (HAT) reactions of metal–oxygen intermediates such as metal-oxo, -hydroxo and -superoxo species have so far been studied extensively. However, HAT reactions of metal-aqua complexes are yet to be studied in comparison with those of the corresponding metal-hydroxo complexes. In this study, a series of Mn(Ⅲ)-aqua complexes, [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) (dpaq^(5R) = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate with a substituent at the 5-position;R = NO_(2), Cl, H, Me and OMe) were synthesized by protonating the corresponding Mn(Ⅲ)-hydroxo complexes, [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+), with trifluoromethanesulfonic acid (HOTf). X-ray crystal structures of both [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+) and [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) complexes showed a mononuclear Mn^(Ⅲ) center in a distorted octahedral environment. The electronic substitution effect of the dpaq ligand on the HAT reactions of [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+) and [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) was then examined by determining the rate constants (k2) of the HAT reactions from 4-methoxy-2,6-di-tert-butylphenol to the Mn(Ⅲ)-hydroxo and -aqua complexes. Hammett plots indicate that HAT from 4-methoxy-2,6-di-tert-butylphenol to [(dpaq^(5R))Mn^(Ⅲ)(OH)]^(+) proceeds via an oxidative asynchronous coupled proton–electron transfer (CPET), whereas HAT from 4-methoxy-2,6-di-tert-butylphenol to [(dpaq^(5R))Mn^(Ⅲ)(OH_(2))]^(2+) proceeds mainly via a basic asynchronous CPET. The contribution of a stepwise electron transfer (ET)/proton transfer (PT) pathway is discussed by comparing the electronic substitution effect on the rate constants of outer-sphere electron transfer and HAT reactions. This study has provided valuable insights into the asynchronous CPET mechanisms of HAT reactions in which the oxidative vs. basic pathways are determined to exhibit reversed electronic substitution effects on HAT reactions of Mn(Ⅲ)-hydroxo and Mn(Ⅲ)-aqua complexes.
