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Laser‐Induced Wurtz‐Type Syntheses with a Metal‐Free Photoredox Catalytic Source of Hydrated Electrons
Author(s) -
Kohlmann Tim,
Kerzig Christoph,
Goez Martin
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201901618
Subject(s) - chemistry , photochemistry , micelle , flash photolysis , solvated electron , radical , catalysis , electron donor , moiety , electron transfer , radiolysis , kinetics , organic chemistry , reaction rate constant , aqueous solution , physics , quantum mechanics
Upon irradiation with ns laser pulses at 355 nm, 2‐aminoanthracene in SDS micelles readily produces hydrated electrons. These “super‐reductants” rapidly attack substrates such as chloro‐organics and convert them into carbon‐centred radicals through dissociative electron transfer. For a catalytic cycle, the aminoanthracene needs to be restored from its photoionization by‐product, the radical cation, by a sacrificial donor. The ascorbate monoanion can only achieve this across the micelle–water interface, but the monoanion of ascorbyl palmitate results in a fully micelle‐contained regenerative electron source. The shielding by the micelle in the latter case not only increases the life of the catalyst but also strongly suppresses the interception of the carbon‐centred radicals by the hydrogen‐donating ascorbate moiety; and in conjunction with the high local concentrations effected by the pulsed laser, termination by radical dimerization thus dominates. We have obtained a complete and consistent picture through monitoring the individual steps and the assembled system by flash photolysis on fast and slow timescales, from microseconds to minutes; and in preparative studies on a variety of substrates, we have achieved up to quantitative dimerization with a turnover on the order of 1 mmol per hour.