反芳香族B,N-カルベンσ配位子の開発と常磁性/アニオン性金錯体の合成と物性解明

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The interplay of aromaticity and antiaromaticity of conjugated π systems is a crucial design strategy for tuning light-initiated electron-transfer properties in designing functional molecules. For transition metal (TM) photocatalysts, while heterocyclic aromatic ligands are widely used for modulation of their (photo)redox behaviors, the effect of antiaromatic ligands remains poorly understood due to a lack of synthetic methodologies. This project proposed a design and synthesis to isolate radical and anionic gold complexes bearing a 4π B, N-heterocyclic Carbene (BNC). The expected antiaromaticity and the inclusion of boron atoms in BNC results in its super π-accepting and σ-donating abilities which are ideal to stabilize and tune unusual oxidation states and radical behaviors of the metal.The synthesis of several derivatives of BNC Au(I) complexes were established. A 2e reduction of the (BNC-Cl)AuL complex by lithium allowed isolation of a bright orange lithium aurate complex Li[(BNC)AuL]. Computational analysis indicated that, despite of the 4π electron counting, the neutral BNC ligand on Au(I) is mostly non-aromatic in character, due to the localized BN π bonds. After reduction, the gold center remained as +I, whereas the BNC moiety became a 6π aromatic system. In particular, the occupied p orbital at the ligating carbon center was shown to interact strongly with the Au(I) 6p orbital with an interaction energy between 15.5 kcal/mol. This result showed that the gold(I) can form multiple bonds with ligand through its 6p orbital ligands instead of 5d orbitals.