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

Abstract

Reaction of [WVIO2(acac)2] (Hacac=acetylacetone) with salan‐type dibasic tetradentate ONNO donor Mannich bases derived from ethylenediamine, formaldehyde and 2,4‐di‐tert‐butylphenol (H2L1), 2‐tert‐butyl‐4‐methylphenol (H2L2), 2,4‐dimethylphenol (H2L3) and 2,4‐dichlorophenol (H2L4) in a 1 : 1 ([WVIO2(acac)2] : H2L) molar ratio in refluxing MeOH gave the corresponding cis‐dioxidotungsten(VI) complexes [WVIO2L1] (1), [WVIO2L2] (2), [WVIO2L3] (3) and [WVIO2L4] (4), respectively. Characterization by elemental analysis, various spectroscopic (FT‐IR, UV‐vis, 1H and 13C 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‐WO2 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.

Substituent Controlled Synthesis of Dioxidomolybdenum(VI) Complexes of N,N,N’,N’‐Tetrakis(2‐Hydroxyl‐3,5‐Disubstitutedbenzyl)‐1,2‐Diaminoethane, Their Trans‐Metalation to Oxidovanadium(V) Complexes and Biocatalytic Applications

“…This information is in accordance with the transformation of oxidovanadium(V) complex to oxidoperoxidovanadium(V) form. [41b] In support of the transformation of oxidovanadium(V) complex to oxidoperoxidovanadium(V) upon addition of H 2 O 2 , 51 V NMR of complex 10 was also recorded in the presence of H 2 O 2 (Figure 16). Adding 10 mmol 30 % aqueous H 2 O 2 to 2 mmol of 10 in d 6 -[DMSO] did not show any change in the signal, however, addition of 100 mmol H 2 O 2 caused the appearance of another signal of high intensity at À 496 ppm.…”

“…, respectively, with α-cis, symmetric isomeric structure [51,54] where ligands behave as dibasic ONNO tetradentate. On the other hand, the t-butyl group at 3-and 5-positions or t-butyl at 3-and methyl group at 5-positions of phenol, resulted in the formation of…”

“…Using N,N,N’,N’‐tetrakis(2‐hydroxy‐3,5‐disubstitutedbenzyl)‐1,2‐diaminoethane, a N 2 O 4 donor tetrabasic hexadentate ligands having smaller spacer and different substituents on the phenol moieties we have been able to isolate two different types of complexes as was aimed in the introduction. The methyl or chloro substituents at 3‐ and 5‐positions gave Type 1 complexes [(Mo VI O 2 )H 2 en(3,5‐dmb) 4 ] ( 3 ) and [(Mo VI O 2 )H 2 en(3,5‐dcb) 4 ] ( 4 ), respectively, with α‐ cis , symmetric isomeric structure [51,54] where ligands behave as dibasic ONNO tetradentate. On the other hand, the t ‐butyl group at 3‐ and 5‐positions or t ‐butyl at 3‐ and methyl group at 5‐positions of phenol, resulted in the formation of Type 2 complexes, [{Mo VI O 2 (MeOH)}H 2 en(3,5‐dtbb) 4 ] ( 1 ) and [{Mo VI O 2 (MeOH)}H 2 en(3‐tb,5‐mb) 4 ] ( 2 ), respectively.…”

“…These structures belong to α-cis, symmetric type, a common isomeric form found in most complexes having cis-[MO 2 ] (M = V, Mo and W) structure and two nitrogen atoms are in a cis-α type binding mode. [50][51][52][53][54] The β-cis, asymmetric form along with one terminal O of cis-[MoO 2 ] trans to N and other one trans to O has been observed in complexes where more steric back bone like homopiperazine in place of ethylene was present. [7] Trans influence is evident in the link distances of the Mo to nitrogen atoms.…”

“…NMR study of vanadium complexesThe51 V NMR spectra of all complexes(7)(8)(9)(10)(11)(12) were measured in d 6 -[DMSO], except 11 which was recorded in CDCl 3 , and the data are summarized in Table5. Complexes 7-10 exhibit only one signal between À 471 to À 485 ppm while complexes 11 and 12 display two signals of almost same intensity.…”