Abstract
Highly reducing or oxidizing photocatalysts are a fundamental challenge in photochemistry. Only a few transition metal complexes with Earth-abundant metal ions have so far advanced to excited state oxidants. All these photocatalysts require high-energy light for excitation, and their oxidizing power has not been fully exploited due to energy dissipation before reaching the photoactive state. Here we demonstrate that the complex [Mn(dgpy)2]4+, based on Earth-abundant manganese and the tridentate 2,6-diguanidylpyridine ligand (dgpy), evolves to a luminescent doublet ligand-to-metal charge transfer (2LMCT) excited state (1,435 nm, 0.86 eV) with a lifetime of 1.6 ns after excitation with low-energy near-infrared light. This 2LMCT state oxidizes naphthalene to its radical cation. Substrates with extremely high oxidation potentials up to 2.4 V enable the [Mn(dgpy)2]4+ photoreduction via a high-energy quartet 4LMCT excited state with a lifetime of 0.78 ps, proceeding via static quenching by the solvent. This process minimizes free energy losses and harnesses the full photooxidizing power, and thus allows oxidation of nitriles and benzene using Earth-abundant elements and low-energy light.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
All data generated or analysed during this study are included in this published Article or its Supplementary Information files, which include irradiations under various conditions (light sources, substrates), luminescence and TA spectroscopic data and conductivity data. Raw data for the figures and supplementary figures and Cartesian coordinates for the optimized structures are also available from Figshare (https://doi.org/10.6084/m9.figshare.24886530). Source data are provided with this paper.
References
Prier, C. K., Rankic, D. A. & MacMillan, D. W. C. Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis. Chem. Rev. 113, 5322–5363 (2013).
Romero, N. A. & Nicewicz, D. A. Organic photoredox catalysis. Chem. Rev. 116, 10075–10166 (2016).
Liu, Y. Z., Persson, P., Sundström, V. & Wärnmark, K. Fe N-heterocyclic carbene complexes as promising photosensitizers. Acc. Chem. Res. 49, 1477–1485 (2016).
Larsen, C. B. & Wenger, O. S. Photoredox catalysis with metal complexes made from Earth-abundant elements. Chem. Eur. J. 24, 2039–2058 (2018).
Wenger, O. S. Photoactive complexes with Earth-abundant metals. J. Am. Chem. Soc. 140, 13522–13533 (2018).
Otto, S. et al. Understanding and exploiting long-lived near-infrared emission of a molecular ruby. Coord. Chem. Rev. 359, 102–111 (2018).
Förster, C. & Heinze, K. Photophysics and photochemistry with Earth-abundant metals – fundamentals and concepts. Chem. Soc. Rev. 49, 1057–1070 (2020).
Dierks, P., Vukadinovic, Y. & Bauer, M. Photoactive iron complexes: more sustainable, but still a challenge. Inorg. Chem. Front. 9, 206–220 (2022).
Kitzmann, W. R., Ramanan, C., Naumann, R. & Heinze, K. Molecular ruby: exploring the excited state landscape. Dalton Trans. 51, 6519–6525 (2022).
Kitzmann, W. R., Moll, J. & Heinze, K. Spin-flip luminescence. Photochem. Photobiol. Sci. 21, 1309–1331 (2022).
Sinha, N. & Wenger, O. S. Photoactive metal-to-ligand charge transfer excited states in 3d6 complexes with Cr0, MnI, FeII, and CoIII. J. Am. Chem. Soc. 45, 4903–4920 (2023).
Sharma, N. et al. Long-lived photoexcited state of a Mn(IV)-oxo complex binding scandium ions that is capable of hydroxylating benzene. J. Am. Chem. Soc. 140, 8405–8409 (2018).
Tzirakis, M. D., Lykakis, I. N. & Orfanopoulos, M. Decatungstate as an efficient photocatalyst in organic chemistry. Chem. Soc. Rev. 38, 2609–2621 (2009).
Yu, D. et al. Luminescent tungsten(vi) complexes as photocatalysts for light-driven C–C and C–B bond formation reactions. Chem. Sci. 11, 6370–6382 (2020).
Zhang, K., Chang, L., An, Q., Wang, X. & Zuo, Z. Dehydroxymethylation of alcohols enabled by cerium photocatalysis. J. Am. Chem. Soc. 141, 10556–10564 (2019).
Yang, Q. et al. Photocatalytic C–H activation and the subtle role of chlorine radical complexation in reactivity. Science 372, 847–852 (2021).
Yatham, V. R., Bellotti, P. & König, B. Decarboxylative hydrazination of unactivated carboxylic acids by cerium photocatalysis. Chem. Commun. 55, 3489–3492 (2019).
West, J. G., Bedell, T. A. & Sorensen, E. J. The uranyl cation as a visible-light photocatalyst for C(sp3)–H fluorination. Angew. Chem. Int. Ed. 55, 8923–8927 (2016).
Abderrazak, Y., Bhattacharyya, A. & Reiser, O. Visible-light-induced homolysis of earth-abundant metal-substrate complexes: a complementary activation strategy in photoredox catalysis. Angew. Chem. Int. Ed. 60, 21100–21115 (2021).
Zhang, Y., Petersen, J. L. & Milsmann, C. A luminescent zirconium(IV) complex as a molecular photosensitizer for visible light photoredox catalysis. J. Am. Chem. Soc. 138, 13115–13118 (2016).
Zhang, Y., Lee, T. S., Petersen, J. L. & Milsmann, C. A zirconium photosensitizer with a long-lived excited state: mechanistic insight into photoinduced single-electron transfer. J. Am. Chem. Soc. 140, 5934–5947 (2018).
Pal, A. K., Li, C., Hanan, G. S. & Zysman-Colman, E. Blue-emissive cobalt(III) complexes and their use in the photocatalytic trifluoromethylation of polycyclic aromatic hydrocarbons. Angew. Chem. Int. Ed. 57, 8027–8031 (2018).
Chábera, P. et al. A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature 543, 695–699 (2017).
Kjær, K. S. et al. Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science 363, 249–253 (2019).
Rosemann, N. W. et al. Tracing the full bimolecular photocycle of iron(III)−carbene light harvesters in electron-donating solvents. J. Am. Chem. Soc. 142, 8565–8569 (2020).
Aydogan, A. et al. Accessing photoredox transformations with an iron(III) photosensitizer and green light. J. Am. Chem. Soc. 143, 15661–15673 (2021).
Steube, J. et al. Janus-type emission of a cyclometalated iron(iii) complex. Nat. Chem. 45, 468–474 (2023).
Stevenson, S. M., Shores, M. P. & Ferreira, E. M. Photooxidizing chromium catalysts for promoting radical cation cycloadditions. Angew. Chem. Int. Ed. 54, 6506–6510 (2015).
Sittel, S., Naumann, R. & Heinze, K. Molecular rubies in photoredox catalysis. Front. Chem. 10, 887439 (2022).
Bürgin, T. H., Glaser, F. & Wenger, O. S. Shedding light on the oxidizing properties of spin-flip excited states in a CrIII polypyridine complex and their use in photoredox catalysis. J. Am. Chem. Soc. 144, 14181–14194 (2022).
Sittel, S. et al. Visible-light induced fixation of SO2 into organic molecules with polypyridine chromium(III) complexes. Chem. Cat. Chem. 15, e202201562 (2023).
Li, C., Kong, X. Y., Tan, Z. H., Yang, C. T. & Soo, H. S. Emergence of ligand-to-metal charge transfer in homogeneous photocatalysis and photosensitization. Chem. Phys. Rev. 3, 021303 (2022).
Förster, C. & Heinze, K. Bimolecular reactivity of 3d metal-centered excited states (Cr, Mn, Fe, Co). Chem. Phys. Rev. 3, 041302 (2022).
Connelly, N. G. & Geiger, W. E. Chemical redox agents for organometallic chemistry. Chem. Rev. 96, 877–910 (1996).
Kim, D. & Teets, T. S. Strategies for accessing photosensitizers with extreme redox potentials. Chem. Phys. Rev. 3, 021302 (2022).
Choi, G. J., Zhu, Q., Miller, D. C., Gu, C. J. & Knowles, R. R. Catalytic alkylation of remote C–H bonds enabled by proton-coupled electron transfer. Nature 539, 268–271 (2016).
Tlili, A. & Lakhdar, S. Acridinium salts and cyanoarenes as powerful photocatalysts: opportunities in organic synthesis. Angew. Chem. Int. Ed. 60, 19526–19549 (2021).
Natarajan, P. & König, B. Excited-state 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ*) initiated organic synthetic transformations under visible-light irradiation. Eur. J. Org. Chem. 2021, 2145–2161 (2021).
Huang, H. & Lambert, T. H. Electrophotocatalytic SNAr reactions of unactivated aryl fluorides at ambient temperature and without base. Angew. Chem. Int. Ed. 59, 658–662 (2020).
Huang, H. et al. Electrophotocatalysis with a trisaminocyclopropenium radical dication. Angew. Chem. Int. Ed. 58, 13318–13322 (2019).
Huang, H. & Lambert, T. H. Electrophotocatalytic acetoxyhydroxylation of aryl olefins. J. Am. Chem. Soc. 143, 7247–7252 (2021).
Cotic, A. et al. Anti-dissipative strategies toward more efficient solar energy conversion. J. Am. Chem. Soc. 145, 5163–5173 (2023).
Penfold, T. J., Gindensperger, E., Daniel, C. & Marian, C. M. Spin-vibronic mechanism for intersystem crossing. Chem. Rev. 118, 6975–7025 (2018).
Auböck, G. & Chergui, M. Sub-50-fs photoinduced spin crossover in Fe(bpy3)2+. Nat. Chem. 7, 629–633 (2015).
Juban, E. A. & McCusker, J. K. Ultrafast dynamics of 2E state formation in Cr(acac)3. J. Am. Chem. Soc. 127, 6857–6865 (2005).
Wang, C. et al. Efficient triplet-triplet annihilation upconversion sensitized by a chromium(III) complex via an underexplored energy transfer mechanism. Angew. Chem. Int. Ed. 61, e202202238 (2022).
Dose, E. V., Hoselton, M. A., Sutin, N., Tweedle, M. F. & Wilson, L. J. Dynamics of intersystem crossing processes in solution for six-coordinate d5, d6, and d7 spin-equilibrium metal complexes of iron(III), iron(II), and cobalt(II). J. Am. Chem. Soc. 100, 1141–1147 (1978).
Siddique, Z. A., Yamamoto, Y., Ohno, T. & Nozaki, K. Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds. Inorg. Chem. 42, 6366–6378 (2003).
Iwamura, M., Takeuchi, S. & Tahara, T. Real-time observation of the photoinduced structural change of bis(2,9-dimethyl-1,10-phenanthroline)copper(I) by femtosecond fluorescence spectroscopy: a realistic potential curve of the Jahn–Teller distortion. J. Am. Chem. Soc. 129, 5248–5256 (2007).
Shaw, G. B. et al. Ultrafast structural rearrangements in the MLCT excited state for copper(I) bis-phenanthrolines in solution. J. Am. Chem. Soc. 129, 2147–2160 (2007).
Gonçalves, P. J. De, Boni, L., Borissevitch, I. E. & Zílio, S. C. Excited state dynamics of meso-tetra(sulphonatophenyl) metalloporphyrins. J. Phys. Chem. A 112, 6522–6526 (2008).
Dorn, M. et al. A vanadium(III) complex with blue and NIR-II spin-flip luminescence in solution. J. Am. Chem. Soc. 142, 7947–7955 (2020).
Antolini, C. et al. Photochemical and photophysical dynamics of the aqueous ferrate(VI) ion. J. Am. Chem. Soc. 144, 22514–22527 (2022).
East, N. R., Förster, C., Carrella, L. M., Rentschler, E. & Heinze, K. The full d3–d5 redox series of mononuclear manganese complexes: geometries and electronic structures of [Mn(dgpy)2]n+. Inorg. Chem. 61, 14616–14625 (2022).
Holleman, A. F. Lehrbuch der Anorganischen Chemie 101 edn (eds Wiberg E. & Wiberg N.) (Walter de Gruyter Verlag, 1995).
Troian-Gautier, L. et al. Halide photoredox chemistry. Chem. Rev. 119, 4628–4683 (2019).
Ward, W. M., Farnum, B. H., Siegler, M. & Meyer, G. J. Chloride ion-pairing with Ru(II) polypyridyl compounds in dichloromethane. J. Phys. Chem. A 117, 8883–8894 (2013).
Li, P., Deetz, A. M., Hu, J., Meyer, G. J. & Hu, K. Chloride oxidation by one- or two-photon excitation of N‑phenylphenothiazine. J. Am. Chem. Soc. 144, 17604–17610 (2022).
Harris, J. P. et al. Near-infrared 2Eg → 4A2g and visible LMCT luminescence from a molecular bis-(tris(carbene)borate) manganese(IV) complex. Can. J. Chem. 95, 547–552 (2017).
Reichenauer, F. et al. Strongly red-emissive molecular ruby [Cr(bpmp)2]3+ surpasses [Ru(bpy)3]2+. J. Am. Chem. Soc. 143, 11843–11855 (2021).
Otto, S. et al. [Cr(ddpd)2]3+: a molecular, water-soluble, highly NIR-emissive ruby analogue. Angew. Chem. Int. Ed. 54, 11572–11576 (2015).
Fuchigami, T., Inagi, S. & Atobe, M. (eds) Fundamentals and Applications of Organic Electrochemistry Appendix B, 217–222 (John Wiley & Sons, 2015).
Romero, N. A., Margrey, K. A., Tay, N. E. & Nicewicz, D. A. Site-selective arene C-H amination via photoredox catalysis. Science 349, 1326–1330 (2015).
Pistritto, V. A., Liu, S. & Nicewicz, D. A. Mechanistic investigations into amination of unactivated arenes via cation radical accelerated nucleophilic aromatic substitution. J. Am. Chem. Soc. 144, 15118–15131 (2022).
Foley, J. K., Korzeniewski, C. & Pons, S. Anodic and cathodic reactions in acetonitrile/tetra-n-butylammonium tetrafluoroborate: an electrochemical and infrared spectroelectrochemical study. Can. J. Chem. 66, 201–206 (1988).
Hammerich, O. & Parker, V. D. Reaction of the anthracene cation radical with acetonitrile. A novel anodic acetamidation. J. Chem. Soc. Chem. Commun. 1974, 245–246 (1974).
Shen, T. & Lambert, T. H. C–H amination via electrophotocatalytic Ritter-type reaction. J. Am. Chem. Soc. 143, 8597–8602 (2021).
Jones, R. W. et al. Direct determination of the rate of intersystem crossing in a near-IR luminescent Cr(III) triazolyl complex. J. Am. Chem. Soc. 145, 12081–12092 (2023).
Schröder, D., Shaik, S. & Schwarz, H. Two-state reactivity as a new concept in organometallic chemistry. Acc. Chem. Res. 33, 139–145 (2000).
Geary, W. J. The use of conductivity measurements in organic solvents for the characterisation of coordination compounds. Coord. Chem. Rev. 7, 81–122 (1971).
Basu, U., Otto, S., Heinze, K. & Gasser, G. Biological evaluation of the NIR-emissive ruby analogue [Cr(ddpd)2][BF4]3 as a photodynamic therapy photosensitizer. Eur. J. Inorg. Chem. 2019, 37–41 (2019).
Kavarnos, G. J. & Turro, N. Photosensitization by reversible electron transfer: theories, experimental evidence, and examples. Chem. Rev. 86, 401–449 (1986).
Van Duyne, R. P. & Reilly, C. N. Low-temperature electrochemistry. I. Characteristics of electrode reactions in the absence of coupled chemical kinetics. Anal. Chem. 44, 142–152 (1972).
Fulmer, G. R. et al. NMR chemical shifts of trace impurities: common laboratory solvents, organics, and gases in deuterated solvents relevant to the organometallic chemist. Organometallics 29, 2176–2179 (2010).
Snellenburg, J. J., Laptenok, S., Seger, R., Mullen, K. M. & van Stokkum, I. H. M. Glotaran: a Java-based graphical user interface for the R package TIMP. J. Stat. Softw. 49, 1–22 (2012).
UHP-T-LA LED: ultra high power collimated LED array light source. Prizmatix https://www.prizmatix.com/LEDUHP/LED-UHP-TLA.aspx (2024).
Neese, F. Software update: the ORCA program system—version 5.0. WIREs Comput. Mol. Sci. 12, e1606 (2022).
Becke, A. D. Density‐functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 98, 5648–5652 (1993).
Miehlich, B., Savin, A., Stoll, H. & Preuss, H. Results obtained with the correlation energy density functionals of Becke and Lee, Yang and Parr. Chem. Phys. Lett. 157, 200–206 (1989).
Lee, C., Yang, W. & Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 37, 785–789 (1988).
Neese, F., Wennmohs, F., Hansen, A. & Becker, U. Efficient, approximate and parallel Hartree–Fock and hybrid DFT calculations. A ‘chain-of-spheres’ algorithm for the Hartree–Fock exchange. Chem. Phys. 356, 98–109 (2009).
Izsák, R. & Neese, F. An overlap fitted chain of spheres exchange method. J. Chem. Phys. 135, 144105 (2011).
Pantazis, D. A., Chen, X.-Y., Landis, C. R. & Neese, F. All-electron scalar relativistic basis sets for third-row transition metal atoms. J. Chem. Theory Comput. 4, 908–919 (2008).
Miertus, S., Scrocco, E. & Tomasi, J. Electrostatic interaction of a solute with a continuum: a direct utilization of ab initio molecular potentials for the prevision of solvent effects. Chem. Phys. 55, 117–129 (1981).
Barone, V. & Cossi, M. Quantum calculation of molecular energies and energy gradients in solution by a conductor solvent model. J. Phys. Chem. A 102, 1995–2001 (1998).
Weigend, F. Accurate Coulomb-fitting basis sets for H to Rn. Phys. Chem. Chem. Phys. 8, 1057–1065 (2006).
Weigend, F. & Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: design and assessment of accuracy. Phys. Chem. Chem. Phys. 7, 3297–3305 (2005).
Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132, 154104 (2010).
Grimme, S., Ehrlich, S. & Goerigk, L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 32, 1456–1465 (2011).
Plasser, F. TheoDORE. http://theodore-qc.sourceforge.net (2024).
Plasser, F. TheoDORE: a toolbox for a detailed and automated analysis of electronic excited state computations. J. Chem. Phys. 152, 084108 (2020).
Hess, B., Kutzner, C., van der Spoel, D. & Lindahl, E. GROMACS 4: algorithms for highly efficient, load-balanced, and scalable molecular simulation. J. Chem. Theory Comput. 4, 435–447 (2008).
Jorgensen, W. L., Maxwell, D. S. & Tirado-Rives, J. Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. J. Am. Chem. Soc. 118, 11225–11236 (1996).
Shao, Y. et al. Advances in molecular quantum chemistry contained in the Q-Chem 4 program package. Mol. Phys. 113, 184–215 (2015).
Darden, T., York, D. & Pedersen, L. Particle mesh Ewald: an N⋅log(N) method for Ewald sums in large systems. J. Chem. Phys. 98, 10089 (1993).
Allen, M. & Tildesley, D. Computer Simulations of Liquids 2nd edn (Oxford Academic, 2017).
Hess, B., Bekker, H., Berendsen, H. J. & Fraaije, J. G. LINCS: a linear constraint solver for molecular simulations. J. Comput. Phys. 18, 1463–1472 (1997).
Bussi, G., Donadio, D. & Parrinello, M. Canonical sampling through velocity rescaling. J. Chem. Phys. 126, 014101 (2007).
Berendsen, H. J. C., Postma, J. P. M., DiNola, A. & Haak, J. R. Molecular dynamics with coupling to an external bath. J. Chem. Phys. 81, 3684–3690 (1984).
Acknowledgements
This work was supported by the Max Planck Graduate Center with the Johannes Gutenberg University Mainz (MPGC). N.R.E. is a recipient of a position through the DFG Excellence Initiative by the Graduate School Materials Science in Mainz (GSC 266). This work was further supported by the Deutsche Forschungsgemeinschaft through grant INST 247/1018-1 FUGG to K.H. Parts of this research were conducted using the supercomputer Mogon and advisory services offered by Johannes Gutenberg University Mainz (http://www.hpc.uni-mainz.de) and the supercomputer Elwetritsch and advisory services offered by the Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau (https://hpc.rz.rptu.de), which are members of the Allianz für Hochleistungsrechnen Rheinland-Pfalz (AHRP) and the Gauss Alliance e.V. We thank D. Zorn for performing the HPLC analyses. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the paper.
Author information
Authors and Affiliations
Contributions
N.R.E. performed the syntheses, the reactivity studies, the irradiation experiments and the computational studies. R.N. performed and analysed the luminescence and ultrafast time-resolved experiments and provided data interpretation. C.F. performed and assisted with the computational studies. C.R. assisted with the time-resolved experiments. G.D. performed and analysed the molecular dynamics simulations. K.H. conceptualized the research, conceived the experiments and performed data analyses and interpretation. All authors discussed the results and commented on the paper.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature Chemistry thanks the anonymous reviewer(s) for their contribution to the peer review of this work.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Supplementary Information
Supplementary Figs. 1–57 and Tables 1 and 2.
Supplementary Data 1
Source data of Supplementary Figs. 1–57.
Source data
Source Data Fig. 1
Absorption and emission spectra of [Mn(dgpy)2]4+ and photooxidation of naphthalene.
Source Data Fig. 2
TA spectra of [Mn(dgpy)2]4+ in MeCN and time-dependent DFT transitions of the doublet.
Rights and permissions
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
About this article
Cite this article
East, N.R., Naumann, R., Förster, C. et al. Oxidative two-state photoreactivity of a manganese(IV) complex using near-infrared light. Nat. Chem. (2024). https://doi.org/10.1038/s41557-024-01446-8
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41557-024-01446-8