Biomimetic Oxidative Bromination by cis ‐Dioxidotungsten(VI) Complexes of Salan Type N,N’‐Capped Linear Tetradentate Amino Bisphenol

Reaction of [W VI O 2 (acac) 2 ] (Hacac=acetylacetone) with salan‐type dibasic tetradentate ONNO donor Mannich bases derived from ethylenediamine, formaldehyde and 2,4‐di‐ tert ‐butylphenol (H 2 L 1 ), 2‐ tert ‐butyl‐4‐methylphenol (H 2 L 2 ), 2,4‐dimethylphenol (H 2 L 3 ) and 2,4‐dichlorophenol (H 2 L 4 ) in a 1 : 1 ([W VI O 2 (acac) 2 ] : H 2 L) molar ratio in refluxing MeOH gave the corresponding cis ‐dioxidotungsten(VI) complexes [W VI O 2 L 1 ] ( 1 ), [W VI O 2 L 2 ] ( 2 ), [W VI O 2 L 3 ] ( 3 ) and [W VI O 2 L 4 ] ( 4 ), respectively. Characterization by elemental analysis, various spectroscopic (FT‐IR, UV‐vis, 1 H and 13 C NMR) studies, DFT calculations and single‐crystal X‐ray analysis of 2 and 3 suggest six‐coordinated octahedral α‐ cis (symmetric) isomeric form of the complexes where ligands coordinate through the two phenolate oxygen and two amine nitrogen atoms (in a cis ‐α type symmetric binding mode) with one of the N atoms of the ligand and one of the terminal O atoms of the cis ‐WO 2 group in the axial position. These complexes are potential catalyst precursors for the oxidative bromination of thymol and styrene. Thymol upon bromination gave three products, namely, 2‐bromothymol, 4‐bromothymol, and 2,4‐dibromothymol; later one being the major product. Oxidative bromination of styrene resulted in 2‐bromo‐1‐phenylethanol and 1‐phenylethane‐1,2‐diol; the later one is the result of nucleophilic attack of water on the α as well as β carbons both of the initially formed 1,2‐dibromo‐1‐phenylethane.