Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)

Fayad, Remi; Engl, Sebastian; Danilov, Evgeny O.; Hauke, Cory E.; Reiser, Oliver; Castellano, Felix N.

doi:10.1021/acs.jpclett.0c01601

Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)

Journal Article · Mon Jun 15 04:00:00 EDT 2020 · Journal of Physical Chemistry Letters

DOI:https://doi.org/10.1021/acs.jpclett.0c01601· OSTI ID:1634193

Fayad, Remi ^[1]; Engl, Sebastian ^[2]; ^[3]; ^[3]; ^[2]; ^[3]

North Carolina State Univ., Raleigh, NC (United States); Princeton University
Univ. of Regensburg (Germany)
North Carolina State Univ., Raleigh, NC (United States)

Developments in the field of photoredox catalysis that leveraged the long-lived excited states of Ir(III) and Ru(II) photosensitizers to enable radical coupling processes paved the way for explorations of synthetic transformations that would otherwise remain unrealized. While first row transition metal photocatalysts have not been as extensively investigated, valuable synthetic transformations covering broad scopes of olefin functionalization have been recently reported featuring photoactivated chlorobis(phenanthroline) Cu(II) complexes. In this study, the photochemical processes underpinning the catalytic activity of [Cu(dmp)₂Cl]Cl (dmp = 2,9-dimethyl-1,10-phenanthroline) were studied. The combined results from static spectroscopic measurements and conventional photochemistry, ultrafast transient absorption, and electron paramagnetic resonance spin trapping experiments strongly support blue light (λ_ex = 427 or 470 nm)-induced Cu–Cl homolytic bond cleavage in [Cu(dmp)₂Cl]⁺ occurring in <100 fs. On the basis of electronic structure calculations, this bond-breaking photochemistry corresponds to the Cl → Cu(II) ligand-to-metal charge transfer transition, unmasking a Cu(I) species [Cu(dmp)₂]⁺ and a Cl atom, thereby serving as a departure point for both Cu(I)- or Cu(II)-based photoredox transformations. No net photochemistry was observed through direct excitation of the ligand-field transitions in the red (λ_ex = 785 or 800 nm), and all combined experiments indicated no evidence of Cu–Cl bond cleavage under these conditions. As a result, the underlying visible light-induced homolysis of a metal–ligand bond yielding a one-electron-reduced photosensitizer and a radical species may form the basis for novel transformations initiated by photoinduced homolysis featuring in situ-formed metal–substrate adducts utilizing first row transition metal complexes.

View Accepted Manuscript (DOE)

Research Organization:: Princeton Univ., NJ (United States); North Carolina State Univ., Raleigh, NC (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: SC0019370; SC0011979

OSTI ID:: 1634193

Alternate ID(s):: OSTI ID: 1643989

Journal Information:: Journal of Physical Chemistry Letters, Journal Name: Journal of Physical Chemistry Letters Vol. 11; ISSN 1948-7185

Publisher:: American Chemical SocietyCopyright Statement

Country of Publication:: United States

Language:: English

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