세미나 신정철 교수 [덕성여자대학교, 화학과] - Photo-induced reductive elimination reactions of organonickel complexes
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일시: 2025년 5월 15일 (목) 오후 5시
장소: 과학관 B133호
초록:
While photoexcitation had become one of the acknowledged methods to activate Ni-catalyzed cross-coupling reactions, factors that determine the photoactivity of organonickel complexes are still under debates. In this presentation, the C-to-Ni charge transfer (CT) states were proposed as key excited states for photo-induced reductive elimination (RE) reactions of nickelacycles, merging two different examples of photo-induced RE reactions: 1) C–S bond-forming RE reactions of NiII complexes1 and 2) C–C bond-forming RE reactions of NiIII and NiIV complexes. 2 The excited-state RE activities of nickelacycles with the thiacycloneophyl (-SC6H4-o-C(CH3)2CH2-) ligand have been measured with five different ancillary ligands, revealing that the RE activities depend on the excitation energy and are independent of the ancillary ligand.1 The electronic structural analyses utilizing electronic absorption (Abs) and magnetic circular dichroism (MCD) spectroscopies in combination with density functional theory (DFT) computations have uncovered that d-d excitations can facilitate Ni–C bond homolysis to generate NiI intermediate via intersystem crossing to a dissociative 3(C-to-Ni CT) state. The sequential C–S bond formation occurring from NiI intermediate eventually produces the cross-coupled product. Alternatively, with cycloneophyl (-C6H4-o-C(CH3)2CH2-) NiIII and NiIV complexes, C-to-Ni CT excited states are directly accessible utilizing visible light sources, exhibiting 105-time enhanced C–C bond-forming activity compared to the ground state.2 These studies emphasize that the RE reactions can be promoted by accessing C-to-Ni CT excited states, showing the significance of an electronic structure level understanding of organometallic reaction mechanisms. Furthermore, an understanding of excited-state RE reactions of organonickel complexes can be utilized to design the Ni-catalyzed cross-coupling reactions incorporating photoexcitations.
References 1. “Ligand-field transition-induced C–S bond formation from nickelacycles” J. Shin, J. Lee, J.-M. Suh, K. Park. Chem. Sci. 2021, 12. 15908-15915. 2. “Correlation between the C–C cross-coupling activity and C-to-Ni charge transfer transition of high-valent Ni complexes” J. Shin, S. Gwon, S. Kim, J. Lee, K. Park. J. Am. Chem. Soc. 2020, 142, 4173-4183.