Novel tungsten catalysts grafted onto polymeric materials: a comparison with phase transfer catalysis

Another Example of the Instability of a Keggin‐Type Heteropolyanion in the Presence of Aqueous Hydrogen Peroxide: From [AsW12O40]3– to Low‐Nuclearity Oxoperoxotungstates – Crystal Structure of [(nHex)4N]3[AsO4{W2O2(μ‐O2)2(O2)2}2]

“…Limonene oxide (0.7:1 to 1:1 mixtures of cis and trans 1,2-epoxide) was characterised and isolated. [13,30] Figure 3 shows that half of the peroxide oxygen is transferred to the olefinic substrate at room temperature, a result which differs from that of the MTO/H 2 O 2 systems. [29,53] Comparative experiments with "CH 3 ReO 3 + 2H 2 O 2 /solvent" show complete transfer of the peroxide oxygen.…”

“…[11,30,42,43,54] The Arquad 2HT ® salts of complexes "AsW 4 " and "AsW 2 " are active precursors and catalysts in olefin oxidation, and form epoxides in the range 20-60°C in two-phase "H 2 O 2 / H 2 O/CHCl 3 or toluene" systems under phase-transfer catalysis (PTC) conditions (see Table 3, Entries 2 to 4). They transfer active oxygen to (R)-(+)-limonene to mostly give the monoepoxides, which are known to be acid-sensitive.…”

“…), the pH of the aqueous phase, the presence of Na + Cl -and the W/X/Q + ratios, and these factors have been analysed in detail by several groups. [30,58,59] For example, it has recently been shown that under PTC, a system such as W/[PO 4 ] 3-/ Q + = 2:1:0.4 was more effective than the system 2:1:2 or 4:1:3 corresponding to the onium salts of "PW 2 " and "PW 4 ", respectively. [31] The use of a large excess of Q + leads to low yields and turnover numbers, as shown previously.…”

“…[31] The use of a large excess of Q + leads to low yields and turnover numbers, as shown previously. [30] If a tetra-n-hexylammonium cation is used instead of Arquad 2HT ® , the conversion is very low (see Table 3, Entry 1).…”

“…[6,25] Although it was formerly accepted that the O-O bond lengths are fairly constant and do not depend on the nature of the metal ligands, we were interested in a systematic study of the heteroligand effect. This is of major importance for catalysis in homogeneous [6,29] or two-phase-medium [6,9,13,22,23,30,31] conditions, for grafting onto (or inserting in) polymeric supports [6,30,[32][33][34][35][36][37][38] or for the comprehensive study of the synthesis of transition-metal-containing mesostructured materials from peroxo species. [39,40] We report here the synthesis and structural characterisation of [(nHex) 4 …”