Zinc Complexes Supported by Hydroxyl‐Containing Schiff‐Base Ligands as Efficient Catalysts for the Borylation of Aryl Iodides

Abstract

AbstractThe application of a series of hydroxyl‐containing Schiff‐base ligands in the synthesis of zinc complexes is reported. The substituents on the benzene rings, the positions of the C=N double bonds, and the ratio of the ligands to ZnEt2 affect the nuclearities of the zinc compounds. Complexes of various nuclearities were prepared, ranging from trinuclear cluster and dinuclear complexes to mononuclear compounds. Treatment of HL1 (HL1=2‐(((1‐(2‐(dimethylamino)ethyl)‐1H‐pyrrol‐2‐yl)methylene) amino)phenol) with one equivalent of ZnEt2 generated a trinuclear compound [(L1)ZnEt]3 ⋅ 0.8Tol (1 ⋅ 0.8Tol). Three dinuclear compounds [(L2)ZnEt]2 ⋅ Tol (2 ⋅ Tol), [(L3)ZnEt]2 (3), and [(L4)ZnEt]2 (4), and two mononuclear complexes [(L5)ZnEt] (5) and [(L6)ZnEt] (6) were formed by the reactions of HL2−HL6, respectively, with ZnEt2. The HL2−HL6 ligands were obtained by slightly modifying the backbone of the HL1 ligand. Three homoleptic compounds [(L1)2Zn] ⋅ THF (7 ⋅ THF), [(L4)2Zn] ⋅ Tol (8 ⋅ Tol), and [(L5)2Zn] (9) were afforded by changing the ratio of the ligands to ZnEt2 from 1 : 1 (compounds 1 ⋅ 0.8Tol, 4 and 5) to 1 : 0.5. The catalytic potential of all nine compounds for the borylation of aryl iodides by B2Pin2 was explored. The catalytic activity of 2 ⋅ Tol was the highest. The reactions catalyzed by 2 ⋅ Tol possess the features of high functional group tolerance and broad substrate scope.