Herein we report on metal-free C-C coupling reactions mediated by the pyridine derivative 2,3,6,7-tetrakis-(tetramethylguanidino) pyridine under the action of visible light. The rate-determining step is the homo lytic N-C bond cleavage of the initially formed V-alkyl pyridinium ion upon excitation with visible light. The released alkyl radicals subsequently dimerize to the C-C coupling product. 2,3,6,7-Tetra- kis(tetramethylguanidino) pyridine, which is a strong electron donor (E_(1/2)(CH_2CI_2) = -0.76 V vs. ferrocene) is oxidized to the dication. For alkyl = benzyl and allyl, relatively high first-order rate constants of 0.23 ±0.03 and 0.13 ±0.03 s~(-1) were determined. Regeneration of neutral 2,3,6,7-tetrakis(tetrame-thylguanidino)-pyridine by reduction allows to drive the process in a cycle.
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