https://scholar.dgist.ac.kr/handle/20.500.11750/12074 Mon, 03 Aug 2026 12:05:30 GMT 2026-08-03T12:05:30Z https://scholar.dgist.ac.kr/handle/20.500.11750/60461 Title: Red-light photoredox catalysis with bridged fluorescein derivatives: mechanistic insights and application to fluoride-responsive photopolymerization Author(s): Lee, Dokyeong; Kim, Hoyun; Jung, Byunghyuck; Yang, Sung Ho; Lee, Hong-In; Lee, Jungkyu K. Abstract: We demonstrated bridged fluoresceins (BFLs) as a class of metal-free red-light photocatalysts that feature structurally tunable and switchable activity in aqueous solutions. Mechanistic studies using photoinitiated radical polymerizations under controlled atmospheres revealed that BFLs engage in efficient oxidative and reductive quenching cycles with co-initiators proceeding through excitation, intersystem crossing, single-electron transfer, and regeneration processes. Notably, molecular oxygen plays dual roles: (i) serving as a co-initiator through O2-derived reactive oxygen species that initiate radical chains, and (ii) functioning as a redox mediator that accelerates regeneration of BFL radical ions. Regarding the structure-performance relationship, bromine substituents on the BFL backbone considerably enhance photocatalytic efficacy by increasing spin-orbit coupling (i.e., the heavy-atom effect), thereby promoting intersystem crossing yield. These findings are supported by thermodynamic and kinetic analyses, including voltammetry, time-resolved photoluminescence under cryogenic conditions, electron paramagnetic resonance (EPR) spectroscopy, and photobleaching studies. We also developed a switchable photoredox catalyst based on a sulfonyl-protected bridged fluorescein. This latent photocatalyst is selectively activated by fluoride ions to restore its photocatalytic activity, enabling red-light photopolymerization. Thus, this work not only offers fundamental mechanistic insights into photoredox catalysis and photoinitiated polymerization, but also establishes design principles for the development of switchable photocatalysts. Thu, 30 Apr 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60461 2026-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60366 Title: Spectroscopic Evidence of a Reduced Alkenylnickel Intermediate in Catalytic Markovnikov-Selective Alkyne Hydroboration Author(s): Lee, Jeong Woo; Kim, Gun Ha; Jeong, Seo Yeong; Jeon, Ji Hwan; Kwon, Hyejin; Kim, Yung Sam; Jung, Byunghyuck; Seo, Sangwon; Rohde, Jan-Uwe; Hong, Sung You Abstract: Nickel-catalyzed hydrofunctionalization reactions, including the hydroboration of alkynes, have been generally proposed to proceed via classical two-electron pathways or, alternatively, through a NiIH-based insertion mechanism. Despite efforts to discern these pathways, explicit spectroscopic observation of NiIH species and relevant mechanistic information on LNiI(alkenyl) species remain lacking. Herein, we provide experimental evidence of formal NiI intermediates, suggestive of a NiIH-based insertion mechanism for alkyne hydroboration. The formation of a NiI catalyst precursor, LnNiI(dpm) (dpm = dipivaloylmethanate anion) and an LnNi(alkenyl) intermediate was confirmed by EPR spectroscopy and HRMS analysis. Their involvement in the catalytic reaction was demonstrated by stoichiometric and catalytic reactivity studies. The origin of the counterintuitive Markovnikov selectivity in the formation of the α-alkenylboronate product was probed by systematic ligand electronic effect studies. Computational analyses rationalize the selectivity by a kinetic preference for formation of the α regioisomer of the LnNi(alkenyl) intermediate through noncovalent interactions. Tue, 31 Mar 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60366 2026-03-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60350 Title: Cu-Catalyzed Stereo- and Regioselective Diborylation and trans-Protoborylation of 1,3-Enynes Author(s): Lee, Yeonjoo; Kim, Minseop; Lee, Dohun; Lee, Yunmi; Seo, Sangwon; Jung, Byunghyuck Abstract: As multifunctional chemical tools, organodiboron compounds present an important challenge in organic synthesis, with respect to their synthesis and functionalization. Although readily available 1,3-enynes have been employed as a platform for various regioselective difunctionalization reactions, the diborylation reactions of 1,3-enynes remain limited, and the installation of a CF3 group is often a prerequisite. In this study, we report a copper-catalyzed selective diborylation reaction of 1,3-enynes to access synthetically useful 1,1- and 1,4-diborylalkenes. The synthetic utility of this method is demonstrated by a gram-scale synthesis of a natural antifouling agent. Furthermore, the Cu-catalyzed trans-protoborylation reaction of aryl-substituted (Z)-enynes is reported. The thorough computational studies and the deuterium-labeling experiments provide insights into the reaction mechanism and the regio- and stereoselectivity of diborylated products. Sat, 28 Feb 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60350 2026-02-28T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58586 Title: Regioselective Transformations of Unsaturated Systems Catalyzed by Low-Valent Nickel: Cycloaddition, Hydrosilylation, and Dicarbofunctionalization Author(s): Kim, Gun Ha; Jeon, Ji Hwan; Jung, Byunghyuck; Rohde, Jan-Uwe; Hong, Sung You Abstract: In this Account, we describe our recent research progress in the development of the functionalization of unsaturated substrates catalyzed by low-valent nickel. In particular, we discuss nickel-catalyzed azide–alkyne cycloaddition (NiAAC), [2 + 2 + 2] cycloaddition of diynes and nitriles, hydrosilylation of alkynes, and dicarbofunctionalization of 1,3-enynes. Moreover, we highlight our mechanistic studies aimed at elucidating catalytically active nickel intermediates, thereby contributing to the understanding and expansion of nickel-catalyzed synthetic methodologies. © 2025. Thieme. All rights reserved. Thu, 31 Jul 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58586 2025-07-31T15:00:00Z