鉗型配位基（Pincer ligands）因其剛性且穩定的三齒配位構型，廣泛應用於過渡金屬錯合物的設計與催化反應中。其結構有助於固定金屬中心並提供良好的電子調控能力，進而提升反應的穩定性與選擇性。本研究延續本實驗室先前對含咔唑（Carbazole）與吡唑（Pyrazole）基團之NNN鉗型配位基的研究，設計三種新型鉗型配位基，分別為NCbzCNHCNAmd、NCbzCNHCPPPh 和 PPPhCNHCNAmd，皆以氮雜環碳烯 (N-heterocyclic carbene, NHC) 為核心架構，並搭配不同電子效應與立體障礙性質的側臂官能基，以探討其對金屬配位行為之影響。所有配位基皆經由 ¹H NMR 鑑定其結構與純度。其中，以強給電子基團為設計主軸的 NCN 配位基，成功合成出對應之 Ni(II) NCN 錯合物，並發現含大立體障礙的側臂基團配位基 (NCNdipp) 有不同的配位模式，並經由X-ray單晶繞射鑑定其結構。 在電化學實驗中，我們於循環伏安法（Cyclic voltammetry）中觀察到可逆的氧化還原峰，顯示該Ni(II) NCN錯合物有氧化為Ni(III)的可能性。並進一步以質譜確認 Ni(III) 錯合物的存在，支持該系列高電子密度配位基能有效穩定高氧化態金屬中心。此結果顯示，該系列配位基設計具有應用於高氧化態金屬錯合物的潛力。 ;Pincer ligands, owing to their rigid and geometrically stable tridentate coordination mode, have been extensively employed in the design of transition metal complexes and in catalytic applications. Their structural framework effectively anchors the metal center and provides enhanced electronic control, thereby improving the stability and selectivity of the associated catalytic transformations. Building upon our previous studies on NNN-type pincer ligands containing carbazole and pyrazole moieties, we have designed three new pincer ligands—NCbzCNHCNAmd, NCbzCNHCPPPh and PPPhCNHCNAmd. These ligands feature a central N-heterocyclic carbene (NHC) core and are functionalized with side arms exhibiting varied electronic effects and steric properties, enabling a systematic investigation of their influence on metal coordination behavior. All ligands were fully characterized by ¹H NMR spectroscopy to confirm their structures and purity. Among them, the NCN-type ligand, which incorporates strongly electron-donating substituents, successfully yielded the corresponding Ni(II) NCN complex. Notably, the ligand bearing a highly sterically hindered side arm (NCNdipp) exhibited an alternative coordination mode, as revealed by single-crystal X-ray diffraction analysis. Electrochemical measurements using cyclic voltammetry revealed a reversible redox couple attributed to the Ni(II)/Ni(III) redox peaks, suggesting the accessibility of the Ni(III) oxidation state. The formation of a Ni(III) species was further confirmed by mass spectrometry, supporting the ability of these electron-rich ligands to stabilize high-valent metal centers. These findings demonstrate the potential of this ligand system in the development of high-valent transition metal complexes.
