Abstract
Gold(III) coordination of new chiral polydentate (N,)N,O‐pyridine based ligands is reported. Successful coordination afforded novel chiral N,N,O‐tridentate Au(III) complexes with the 2‐pyridyl‐6‐[(1S,2S,5R)‐neomenthol‐1‐yl]pyridine ligand (1H, 13C, 15N NMR, HRMS, IR, XRD). The chiral 2‐aryl‐6‐alkylpyridine alcohol ligands were prepared from 2,6‐dibromopyridine by initial stereoselective addition to (–)‐menthone and (+)‐camphor, respectively, and subsequent Suzuki cross‐coupling with a series arylboronic acids. Testing of catalytic activity in propargyl cyclopropanation demonstrated that the new N,N,O‐ligated gold(III) complex was highly catalytic active and outperformed AuCl3.
Highlights
Gold(III) complexes are less developed and have received less attention as catalysts in organic synthesis compared to their gold(I) counterparts
Different from the linear coordination mode of Au(I) complexes, Au(III) complexes prefer a square-planar geometry, which allows for better tuning of the spatial environment of the gold centre by ligand design
Subsequent Suzuki cross-coupling of monobromopyridines 4–5 with various boronic acids A–E gave the new chiral 2-aryl-6-alkylpyridine alcohols 6–7 in moderate to excellent yields (41–99 %)
Summary
Gold(III) complexes are less developed and have received less attention as catalysts in organic synthesis compared to their gold(I) counterparts. Catalysis by gold(III) is still mainly dominated by inorganic gold(III) salts, such as AuCl3 and K(AuCl4).[1] Different from the linear coordination mode of Au(I) complexes, Au(III) complexes prefer a square-planar geometry, which allows for better tuning of the spatial environment of the gold centre by ligand design. The Au(III) complexes may have a greater potential to achieve chemo- and enantioselectivity by being able to bring the ligand(s) closer to the substrate through its square-planar geometry. The Au(III)-ligand concept was mainly developed for bioactive studies. A number of stable Au(III)-ligand complexes were designed as promising candidates for biological testing.[2]
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