Dioxygen Activation with Molybdenum Complexes Bearing Amide-Functionalized Iminophenolate Ligands

Abstract

Two novel iminophenolate ligands with amidopropyl side chains (HL2 and HL3) on the imine functionality have been synthesized in order to prepare dioxidomolybdenum(VI) complexes of the general structure [MoO2L2] featuring pendant internal hydrogen bond donors. For reasons of comparison, a previously published complex featuring n-butyl side chains (L1) was included in the investigation. Three complexes (1–3) obtained using these ligands (HL1–HL3) were able to activate dioxygen in an in situ approach: The intermediate molybdenum(IV) species [MoO(PMe3)L2] is first generated by treatment with an excess of PMe3. Subsequent reaction with dioxygen leads to oxido peroxido complexes of the structure [MoO(O2)L2]. For the complex employing the ligand with the n-butyl side chain, the isolation of the oxidomolybdenum(IV) phosphino complex [MoO(PMe3)(L1)2] (4) was successful, whereas the respective Mo(IV) species employing the ligands with the amidopropyl side chains were found to be not stable enough to be isolated. The three oxido peroxido complexes of the structure [MoO(O2)L2] (9–11) were systematically compared to assess the influence of internal hydrogen bonds on the geometry as well as the catalytic activity in aerobic oxidation. All complexes were characterized by spectroscopic means. Furthermore, molecular structures were determined by single-crystal X-ray diffraction analyses of HL3, 1–3, 9–11 together with three polynuclear products {[MoO(L2)2]2(µ-O)} (7), {[MoO(L2)]4(µ-O)6} (8) and [C9H13N2O]4[Mo8O26]·6OPMe3 (12) which were obtained during the synthesis of reduced complexes of the type [MoO(PMe3)L2] (4–6).

Oxygen Atom Transfer Reactivity of Molybdenum(VI) Complexes Employing Pyrimidine- and Pyridine-2-thiolate Ligands

“…Reduction of 1 – 4 with the electron-rich and sterically less demanding PMe 3 in comparison to PPh 3 led to the monomeric complexes [MoOL 2 (PMe 3 ) 2 ] (L = PymS ( 10 ), PyS ( 11 ), 4-MePyS ( 12 )) and [MoO­(6-MePyS) 2 (PMe 3 )] ( 13 ), as displayed in Scheme . While the latter 16e – species with one coordinated PMe 3 is quite common, − the formation of the 18e – complexes with two coordinated PMe 3 donors was rather unexpected. To the best of our knowledge, this behavior of dioxidomolybdenum­(VI) complexes toward PMe 3 is unique.…”

Nature-Inspired Homogeneous Catalytic Perchlorate Reduction Using Molybdenum Complexes

“…During the reactions in CD 2 Cl 2 , no precipitate is observed, while a small amount of black solid is found in CD 3 CN after 24 h. We ascribe this observation to the formation of Mo V 2 O 3 dimers since we recently observed that they are black or deep purple and hardly soluble in any solvent . For reasons of comparison, Mo VI O 2 complexes with iminophenolate ligands recently published by our group were likewise investigated but did not show any activity toward perchlorate reduction under the applied conditions. , Regardless of the conditions, complex 1 turned out to be a slightly more efficient catalyst than 2 after 24 h.…”

“…22 For reasons of comparison, Mo VI O 2 complexes with iminophenolate ligands recently published by our group were likewise investigated but did not show any activity toward perchlorate reduction under the applied conditions. 29,30 Regardless of the conditions, complex 1 turned out to be a slightly more efficient catalyst than 2 after 24 h.…”

Photo-epoxidation of (α, β)-pinene with molecular O2 catalyzed by a dioxo-molybdenum (VI)-based Metal–Organic Framework

“…This green pathway for the reoxygenation of the metal center has previously been observed for various dioxo-molybdenum complexes in homogeneous and covalently grafted onto Ti and Si oxides allowing a reactivation of the oxidative catalytic process as shown in Fig. 5 [73][74][75][76][77].…”