Dichromatic Photocatalytic Substitutions of Aryl Halides with a Small Organic Dye

Abstract

Photocatalytic bond activations are generally limited by the photon energy and the efficiency of energy and electron transfer processes. Direct two-photon processes provide sufficient energy but the ultra-short lifetimes of the excited states prohibit chemical reactions. The commercial dye 9,10-dicyanoanthracene enabled photocatalytic aromatic substitutions of non-activated aryl halides. This reaction operates under VIS-irradiation via sequential photonic, electronic, and photonic activation of the simple organic dye. The resultant highly reducing excited photocatalyst anion readily effected C-H, C-C, C-P, C-S, and C-B bond formations. Detailed synthetic, spectroscopic, and theoretical studies support a biphotonic catalytic mechanism.

Micellized Tris(bipyridine)ruthenium Catalysts Affording Preparative Amounts of Hydrated Electrons with a Green Light‐Emitting Diode

“…As trapping reagents that avoid the formation of several cross‐coupling products, we selected mesitylacetate MesAc and N ‐methylpyrrole‐2‐carboxylate NMPCA. With the former, all ring positions except meta are occupied; with the latter, it is well known that the addition of radicals to pyrroles almost exclusively occurs at the ring position adjacent to the nitrogen atom . Proof of principle for the viability of our approach is obtained from the NMR spectra in SI‐5.3.…”

“…meta are occupied;with the latter,i tiswell known that the addition of radicals to pyrroles almoste xclusively occurs at the ring position adjacent to the nitrogen atom. [38][39][40][41][42][43] Proof of principle fort he viability of our approachi so btained from the NMR spectra in SI-5.3. In the case of MesAc, the deceleration of the traget reactionb yt he overcrowdedt rapping reagent only allows am oderate yield of the coupling product, with benzoate remaining the main product;h owever, the sterically less demanding NMPCA turns the table and approximately reverses the product distribution (Scheme3).…”

A Green‐LED Driven Source of Hydrated Electrons Characterized from Microseconds to Hours and Applied to Cross‐Couplings

“…Especially promisinga sc oupling reagents are N-alkylated pyrroles,b ecause they are very reactive towards radicals and exclusively afford 2-substituted products;h ence,e ven at moderate concentrationst hey permit effective and selective radical usage. [25][26][27][28][29][30] In our strongly basic aqueous solutions, N-methyl-2-pyrrolecarboxylic acid (NMPCA)i sp articularly well suited for intercepting the e aq C À -generated radicals, as it combines this reactivity with excellent solubility.M oreover,i ts deprotonated carboxylate substituent increases its hydrophilicity,s uch as to ensurei ts exclusion from the micelles, in which it might otherwise interfere with the electron source. Figure 6a demonstrates the successful cross-coupling of NMPCA withC lAc as the radicalp recursor to give 5-(2-carboxymethyl)-N-methylpyrrole-2-carboxylate 1 in am oderate yield of 41 %( for the formulae of all cross-coupling products, see Scheme 1).…”

Laser‐Induced Wurtz‐Type Syntheses with a Metal‐Free Photoredox Catalytic Source of Hydrated Electrons

“…[22][23][24] Ta ble 1c ollectsy ields at illumination end points for a number of synthetic applicationst ested with our systems. Its five times longer optical path length made better use of the laser light by absorbing all of it but influenced the product distribu- tion only marginally,a gain in accordance with the results of SI-4.2.2.…”