Dioxidomolybdenum(VI) and -tungsten(VI) complexes with tripodal amino bisphenolate ligands as epoxidation and oxo-transfer catalysts

Abstract

The molybdenum(VI) and tungsten(VI) complexes [MO 2 (L)] (M= Mo (1), W (2), H 2 L = bis(2-hydroxy-3,5-di-tert-butybenzyl)morpholinylethylamine)) were synthesized and the complexes were used to catalyse oxotransfer reactions, viz. sulfoxidation, epoxidation and benzoin oxidation. For comparison, the same reactions were catalysed using the known complexes [MO 2 (L')] (M= Mo (3), W (4), H 2 L' = bis(2-hydroxy-3,5-di-tertbutybenzyl)ethanolamine) and [MO 2 (L'')] (M= Mo (5), W (6), H 2 L'' = bis(2-hydroxy-3,5-ditert-butybenzyl)diethyleneglycolamine). The oxo atom transfer activity between DMSO and benzoin at 120 °C was identical for all studied catalysts. Reasonable catalytic activity was observed for sulfoxidation by the molybdenum complexes, but all tungsten complexes were found to be inactive. Similarly, the molybdenum complex 1 exhibited relatively good epoxidation activity, while the corresponding tungsten complex 2 catalysed only the epoxidation of cis-cyclooctene with low activity.

Bioinspired Mo, W and V complexes bearing a highly hydroxyl-functionalized Schiff base ligand

“…[36] Oxygen atom transfer activity cis-Dioxidomolybdenum(VI) and -tungsten(VI) complexes are well known to catalyze oxygen atom transfer (OAT) to suitable organic substrates such as, but not limited to, benzoin and triphenylphosphine. [82][83][84][85][86] The propensity of Mo/W compounds to catalyze this particular reaction is not at all surprising considering the role of these metals in enzymes such as DMSO reductase that catalyzes similar reactions. [86] As a Table 5.…”

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

“…The presence of WO 2 has been proposed in the oxidised active sites of tungstoenzymes, and several model complexes have been prepared to understand their redox chemistry [3] . Leaving the chemistry associated with these enzymes, tungsten(VI) complexes having cis ‐[WO 2 ] moiety have mostly been explored for the catalytic epoxidation of alkenes [4–10] . In spite of the good catalytic potentials of these complexes, the growth of the tungsten chemistry, particularly having cis ‐[WO 2 ] moiety is limited [4–13] .…”

“…Leaving the chemistry associated with these enzymes, tungsten(VI) complexes having cis ‐[WO 2 ] moiety have mostly been explored for the catalytic epoxidation of alkenes [4–10] . In spite of the good catalytic potentials of these complexes, the growth of the tungsten chemistry, particularly having cis ‐[WO 2 ] moiety is limited [4–13] . After the first report on dioxidotungsten(VI) complexes of hydrogenated analogue of H 2 salen [N,N’‐ethylenebis(salicylideneimine)] (i.e.…”

Synthesis, Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of (Z)-1-R-2-(4′,4′-Dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ates

“…The cis-orientation of the dioxido unit was confirmed in addition to the presence of trans-spanning N atoms and cis-enolate O-groups. The bond lengths between the metal and these atoms can be compared to structurally related examples and are otherwise typical [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. These data did not show large differences in magnitude throughout the series.…”

“…Indeed, completely insoluble and presumably highly cross-linked products (Section 2.4.1) were isolated [25]. In contrast, complexes 1-4 were useful in oxygen-transfer chemistry (Section 2.4.2), and the activity of these materials parallels similar systems [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]48] in the benchmark formation of benzil from benzoin (Scheme 5).…”