Redox-active ligands – a viable route to reactive main group metal compounds

Briand, Glen G.

doi:10.1039/d3dt03100d

“…Pincer ligands allow more structural variability on the metal atom than porphyrinoids while still benefiting from the chelate effect and potential for redox-activity. [31] We became interested in the tridentate, monoanionic bis(pyridylimino) isoindolide (BPI) ligand, which mimics porphyrinoids in terms of donating atoms and redox-activity. [32] Transition metal complexes of BPI ligands were already applied in asymmetric homogeneous catalysis [33] or artificial photosynthesis, [34] and our group recently investigated the π accepting properties of BPI ligands.…”

Section: Introductionmentioning

confidence: 99%

Visible‐Light Activation of Diorganyl Bis(pyridylimino) Isoindolide Aluminum(III) Complexes and Their Organometallic Radical Reactivity

Wenzel,

Werner,

Allgaier

et al. 2024

Angew Chem Int Ed

0

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We report on the synthesis and characterization of a series of (mostly) air‐stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible‐light excitation. The redox non‐innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon‐centered radicals. The photo‐induced homolytic cleavage of the Al–C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin‐free Giese‐type reactions and carbonyl alkylations under ambient conditions, which both indicated radical‐polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench‐stable aluminum organometallics.

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“…Pinzettenliganden erlauben meist mehr strukturelle Flexibilität am Metallatom als Porphyrine, während der Chelateffekt und eventuell Redoxaktivität erhalten bleiben. [31] Wir fokussierten uns daher auf das tridentate, monoanionische Bis(pyridylimino)isoindolid(BPI)À Ligandensystem, welches Porphyrine in Bezug auf Donoratome und Redoxaktivität nachahmt. [32] Übergangsmetallkomplexe von BPI-Liganden wurden bereits ausgiebig untersucht, beispielsweise im Rahmen asymmetrischer homogener Katalyse, [33] oder künstlicher Photosynthese.…”

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Aktivierung von Diorganyl‐bis(pyridylimino)isoindolid‐Aluminiumkomplexen mit sichtbarem Licht und deren organometallische Radikalreaktivität

Wenzel,

Werner,

Allgaier

et al. 2024

Angewandte Chemie

0

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We report on the synthesis and characterization of a series of (mostly) air‐stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible‐light excitation. The redox non‐innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon‐centered radicals. The photo‐induced homolytic cleavage of the Al–C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin‐free Giese‐type reactions and carbonyl alkylations under ambient conditions, which both indicated radical‐polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench‐stable aluminum organometallics.

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The Role of a Redox‐Active Ligand in Cu(II)‐Nitrenoid Formation and Its Aziridination Reactivity

Mahajan,

Gangwar,

Mondal

2024

ChemCatChem

0

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Metal‐nitrenoid species are the key intermediate in nitrene transfer reactions. The bond formation between the open‐shell transition metal and the nitrene species dictates their overall reactivity. Herein, we present an in‐depth electronic structure investigation to uncover how the formation of a Cu(II)‐nitrenoid species is assisted by redox‐active iminosemiquinone (ISQ) ligand in the [CuII(LISQ)2] complex and impact the nitrene‐transfer reactivity. The reaction energetics of the aziridination reaction between N‐tosyliminophenyliodinane and 4‐chlorostyrene is established by DFT calculations, where the formation of the Cu(II)‐nitrenoid intermediate (Int1) is found to be the rate‐determining step. Based on the natural orbital and spin populations obtained from the ab initio multi‐configurational CASSCF(13,13) calculation, the electronic nature of the elusive Cu(II)‐nitrenoid intermediate (Int1) could be formulated as “imidyl” [(LISQ)(LIBQ)CuII─•NTos] (Tos = Tosyl) species. A weak σ interaction between the Cu(II) center and the N‐atom of the nitrene moiety (Cu 20% + N 29%) involving a Cu–N distance of 1.92 Å defines the Cu‐nitrenoid bonding. The interplay between elongated Cu–N bond and high spin population on N‐atom (+0.96) corroborates its high nitrene transfer ability. Furthermore, the intrinsic bond orbital (IBO) analysis unravels a ligand‐to‐substrate electron transfer mechanism that facilitates the formation of the crucial Cu(II)‐nitrenoid species.

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Redox-active ligands – a viable route to reactive main group metal compounds

Abstract: This article highlights studies that probe the oxidation/reduction of main group metal compounds possessing redox-active ligands and comments on the prospects for this relatively untapped avenue of research.

Cited by 7 publications

References 112 publications

Visible‐Light Activation of Diorganyl Bis(pyridylimino) Isoindolide Aluminum(III) Complexes and Their Organometallic Radical Reactivity

Visible‐Light Activation of Diorganyl Bis(pyridylimino) Isoindolide Aluminum(III) Complexes and Their Organometallic Radical Reactivity

Aktivierung von Diorganyl‐bis(pyridylimino)isoindolid‐Aluminiumkomplexen mit sichtbarem Licht und deren organometallische Radikalreaktivität

The Role of a Redox‐Active Ligand in Cu(II)‐Nitrenoid Formation and Its Aziridination Reactivity

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