Peroxomolybdenum Complexes as Epoxidation Catalysts in Biphasic Hydrogen Peroxide Activation: Raman Spectroscopic Studies and Density Functional Calculations

Abstract

Density functional calculations and Raman spectroscopic data were correlated with the unique catalytic epoxidation activity of peroxomolybdenum complexes [MoO(O 2 ) 2 (O-ER 3 )] (E N, P, As; R n-dodecyl) in a biphasic chloroform ± 1-octene/aqueous hydrogen peroxide system. Crystal structure determinations on [MoO(O 2 ) 2 (OPtBu 3 )(OCMe 2 )] and two complexes containing chelating hemilabile ether ± phosphane oxide and ether ± arsane oxide ligands [MoO(O 2 ) 2 -{iPr 2 E(O)CH 2 CH 2 OCH 3 }] (E P, As) are reported. A mechanistic study with these model complexes reveals the importance of free coordination sites for peroxide activation. Calculations and Raman spectroscopic data indicate the tendency of coordinatively unsaturated species [MoO(O 2 ) 2 (L)] to dimerize in noncoordinating solvents. The catalytic activity in the presence of water as competing ligand could be correlated with the calculated proton affinity of the ligands OER 3 (R N, P, As). Elucidation of the vibrational behavior of the structurally characterized peroxo complexes was supported by normal-coordinate analyses.

Olefin Epoxidation with Transition Metal η2-Peroxo Complexes: The Control of Reactivity

“…[8] Beside Herrmann-type diperoxorhenium compounds, [6] Mimoun-type diperoxo complexes of group 6 metals have been utilized as oxidants for olefins. As a promising method based on the stoichiometric epoxidation with Mimoun-type diperoxomolybdenum complexes [MoO(O 2 ) 2 (OPR 3 )] (R ϭ NMe 2 ), [9] a biphasic catalytic system (R ϭ n-dodecyl) has recently been developed [10] and patented by BASF. [11] Furthermore, catalytic methods in one homogeneous phase involving oxo-and diperoxomolybdenum compounds with the hmpa ligand (R ϭ NMe 2 ) [12] and the 3-pyrazolylpyridine-N,NЈ ligand [13] were reported.…”

“…The small reactivity of monoperoxomolybdenum compounds was supported by experiments [10,43] and a recent theoretical [18] study. However, the data provided in Table 3 reveal that the reactivities of the tungsten compounds are different.…”

“…[10,11] Thus, we have investigated the reactivity of the diperoxo complexes [MO(O 2 ) 2 {OE(CH 3 ) 3 }] with M ϭ Cr, Mo, W and with E ϭ N, P, As. The results given in Table 4 are similar for the three metals; we focus on the molybdenum compounds for which the largest differences in the activation barriers are found.…”

“…[16] Note that, in the catalytic systems, the coordination of the oxidant such as hydrogen peroxide, silyl peroxides, or tert-butyl hydroperoxide to the metal center and subsequent proton transfer can yield different species which are potentially more reactive than the parent η 2 -peroxo complex. [10,13,17,21] Unless otherwise Scheme 3. Concepts for the control of reactivity of olefin oxidation with Mimoun-type peroxo complexes stated, transfer of the peroxo oxygen atom, which is located trans to the phosphane oxide, has been considered.…”

Oxidation of Alkenes with H2O2 by an in-Situ Prepared Mn(II)/Pyridine-2-carboxylic Acid Catalyst and the Role of Ketones in Activating H2O2

“…Their relatively low toxicity and cost and the often high turnover numbers (TONs) that can be achieved position manganese-, 4−6 iron-, 7 tungsten-, 8−12 and molybdenum-based 13 catalysts at the focus of current attention. 3 Notable examples are the "off the shelf" systems based on molybdenum and tungsten oxides developed by Payne, 8 Venturello, 9,10 and Noyori 2,11,12 and coworkers and the methyltrioxorhenium (MTO) system developed by Herrmann 14,15 and others.…”