Iridium‐Catalyzed Direct C−H Amidation Polymerization: Step‐Growth Polymerization by C−N Bond Formation via C−H Activation to Give Fluorescent Polysulfonamides

Abstract

We report a powerful strategy for activation of C-H bonds to produce polysulfonamides by an atom-economical and green method using iridium-catalyzed direct C-H amidation polymerization (DCAP). After screening various directing groups, additives, silver salts, concentrations, and temperatures to optimize DCAP, high-molecular-weight (up to 149 kDa) and defect-free polysulfonamides were synthesized from various bis-sulfonyl azides. Although these polymers do not have conventional fluorescent conjugated cores, they emit blue light with large Stokes shifts and high quantum yields upon photoexcitation owing to an excited-state intramolecular proton-transfer process.

Iridium-Catalyzed Direct C–H Amidation Producing Multicolor Fluorescent Molecules Emitting Blue-to-Red Light and White Light

“…24,46,50−54 Inspired by the highly efficient DCA, we recently reported direct C−H amidation polymerization (DCAP) of bis-sulfonyl azides and bis-benzamides to produce polysulfonamides by an atom-economical and green method (Scheme 1b). 55,56 Interestingly, unique intramolecular hydro-gen-bonds are formed between the proton on the sulfonamide group and adjacent carbonyl group throughout the polymer backbone, causing polysulfonamides to undergo an excitedstate intramolecular proton-transfer (ESIPT) process and emit blue-light with high quantum yields. This process occurs when photoexcited molecule emits light with a very large Stokes shift by transfer of protons, leading to keto−enol tautomerization.…”

“…During the last two decades, C–H activation chemistry has gained widespread attention, because it provides an atom- and step-economical route for preparing not only complex molecules, such as natural products and pharmaceuticals, − but also fluorophores that can be applied in organic light-emitting diodes (OLEDs). − In the field of C–H activation chemistry, C–C bond formation has been mainly studied so far, but recently, direct C–H amination/amidation strategies resulting in C–N bond formation have also been actively investigated. − Among them, Chang’s group developed iridium-catalyzed direct C–H amidation (DCA) reactions between sulfonyl azides and arenes containing carbonyl (or imine) directing groups, thus enabling efficient synthesis of various sulfonamides under mild conditions (Scheme a). ,,− Inspired by the highly efficient DCA, we recently reported direct C–H amidation polymerization (DCAP) of bis-sulfonyl azides and bis-benzamides to produce polysulfonamides by an atom-economical and green method (Scheme b). , Interestingly, unique intramolecular hydrogen-bonds are formed between the proton on the sulfonamide group and adjacent carbonyl group throughout the polymer backbone, causing polysulfonamides to undergo an excited-state intramolecular proton-transfer (ESIPT) process and emit blue-light with high quantum yields. This process occurs when photoexcited molecule emits light with a very large Stokes shift by transfer of protons, leading to keto–enol tautomerization.…”

Recent Advances in Using Transition-Metal-Catalyzed C–H Functionalization to Build Fluorescent Materials

“…In 2017, the Choi group used the iridium-catalyzed direct C-H amidation polymerization to prepare fluorescent polysulfonamides (Scheme 90). 86 Polysulfonamides 156 was obtained with higher M n of 59.6 kDa. This polymer showed strong blue emission with a large Stokes shift of 166 nm in THF due to an ESIPT process (Figure 39).…”

Recent Progress in the C−N Bond Formation via High‐Valent Group 9 Cp*M(III)‐Catalyzed Directed sp2 C−H Activation

“…Choi et al [49] employed organic azides 139 for the polymerization reaction by using the amidation reaction to synthesize polysulfonamides 140 (Scheme 45). These defect-free polysulfonamides can be synthesized in a high molecular-weight (up to 149 kDa).…”

“…Choi et al [49] . employed organic azides 139 for the polymerization reaction by using the amidation reaction to synthesize polysulfonamides 140 (Scheme 45).…”