Replacement of an Oxo by an Imido Group in Oxotransferase Model Compounds: Influence on the Oxygen Atom Transfer

Abstract

Treatment of [MoO(N-t-Bu)Cl(2)(dme)] (dme = dimethoxyethane) with 2 equiv of the potassium salts of Schiff base ligands of the type KArNC(CH(3))CHC(CH(3))O afforded oxo imido molybdenum(VI) compounds [MoO(N-t-Bu)L(2)] {1, with Ar = phenyl (L(Ph)), 2 with Ar = 2-tolyl (L(MePh)), 3 with Ar = 2,6-dimethylphenyl (L(Me2Ph)) and 4 with Ar = 2,6-diisopropylphenyl (L(iPr2Ph))}. We have also prepared related bisimido complexes [Mo(N-t-Bu)(2)L(2) (5 with L = L(Ph), 6 with L = L(MePh), and 7 with L = L(Me2Ph)) by treatment of [Mo(N-t-Bu)(2)Cl(2)(dme)] with 2 equiv of the potassium salt of the respective ligand. 1, 3, 5, and 6 were characterized via single crystal X-ray diffraction. The oxo imido complexes exhibit oxygen atom transfer (OAT) reactivity toward trimethyl phosphine. Kinetic data were obtained for 1 and 3 by UV/vis spectroscopy revealing decreased OAT reactivity in comparison to related dioxo complexes with the same Schiff base ligands and decreased reactivity of 1 versus 3. Cyclic voltammetry was used to probe the electronic situation at the molybdenum center showing reversible reduction waves for 3 and [MoO(2)(L(Me2Ph))(2)] at comparable potentials while 1 exhibits a significant lower potential. Density functional theory (DFT) calculations showed a higher electron density on oxygen in the oxo imido complexes.

Bioinspired functional analogs of the active site of molybdenum enzymes: Intermediates and mechanisms

“…With the imido complex Mo(L 3 ) 2 (N t Bu)O selective oxygen atom transfer to PMe 3 is realized without any hints for imido transfer [82]. This behavior is similar to the reactivity of the imido/oxido di(ˇ-ketiminato) complexes of Mösch-Zanetti [94] but contrasts the imido group transfer reaction of Mo(dtc) 2 (NTs)O to phosphanes observed by Holm [95]. The observed OAT reactivity instead of imido group transfer of Mo(L 3 ) 2 (N t Bu)O fits to the calculated higher energy of its Mo N t Bu * orbital compared with that of its Mo O * orbital as suggested by DFT calculations [82].…”

Dioxygen Activation with Molybdenum Complexes Bearing Amide-Functionalized Iminophenolate Ligands

“…Molybdenum is an earth-abundant transition metal with crucial biological relevance for most organisms including humans [1,2,3]. The molybdenum(VI) dioxido motif, which is widespread in oxygen atom transfer (OAT) enzymes [1,4,5], sparked the intensive investigation of mononuclear dioxidomolybdenum(VI) complexes over the past decades, both in biomimetic chemistry as well as in oxygenation catalysis [2,6,7,8,9,10,11,12,13]. A major drawback in virtually all reported catalytic systems is, however, the necessity of a terminal oxidant [13,14,15,16,17,18,19,20,21].…”

Activation of Molecular Oxygen by a Molybdenum(IV) Imido Compound

“…For this reason, we envisioned to exchange the "spectator" oxido ligand with an electron donating imido group to leave more electron density at the metal to increase π-backbonding, possibly enabling the transfer of the peroxido oxygen atoms. [17][18][19] In contrast to oxido peroxido complexes, which are usually easily accessible via the reaction of MoO3 with H2O2 and appropriate ligand addition, 20,21 the substance class of imido peroxido complexes is so far only accessible via molecular oxygen activation and has not been described.…”