Unusual Nonoctahedral Geometry with Molybdenum Oxoimido Complexes Containing η²-Pyrazolate Ligands

Abstract

The preparation and oxygen-atom-transfer (OAT) reactivity of oxoimido complexes [MoO(N-t-Bu)(t-Bu(2)-4-Rpz)(2)] [where R = H (1), Br (2), and Me (3); t-Bu(2)pz = 3,5-di-tert-butylpyrazolate] are reported. The reaction of the potassium salt of the respective pyrazolate ligands and the molybdenum oxoimido precursor, [MoO(N-t-Bu)Cl(2)(dme)] (dme = dimethoxyethane), in toluene afforded complexes 1-3 in good yields. The complexes were fully characterized by (1)H and (13)C NMR and IR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray crystallography. The solid-state structures reveal that, in each case, the molybdenum center is coordinated by one oxo, one N-t-Bu group, and two sterically demanding pyrazolate ligands via their two adjacent nitrogen atoms in an η(2) fashion. Coordination around the metal center is severely distorted from octahedral and might be seen as closely approaching a distorted trigonal-prismatic geometry, which is relevant to the active site of dimethyl sulfoxide reductase in its oxidized form. The potential utility of all of the complexes 1-3 for OAT reactivity toward PMe(3) at room temperature is examined, and plausible mechanistic pathways are explored by density functional theory calculations. Furthermore, the complexes reported here open a new and convenient entry into mixed oxoimidomolybdenum complexes.

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

“…: 902 † , Figure S19, SI) and 890 cm -1 , respectively, which is 20-30 wavenumbers lower in energy compared to stretching frequencies observed for previously reported Mo oxido imido compounds. 19,27 This corroborates a weakened Mo=O bond, as also observed by X-ray crystallography (vide infra). The ν(O-O) band in 3a is observed at 924 cm -1 (calc.…”

“…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.…”

A Linear Trinuclear Oxidodiperoxido‐molybdenum(VI) Complex with Single Triazole Bridges: Catalytic Activity in Epoxidation, Alcoholysis, and Acetalization Reactions

“…Although a handful of Mo VI and W VI discrete complexes are known in which pyrazole derivatives are N,N‐chelated to the same metal center, none of these reported complexes contain inorganic peroxido ligands in the coordination sphere. Examples of discrete complexes of the former kind have, for example, been reported with 3,5‐dimethylpyrazole, 3,5‐di‐ tert ‐butylpyrazole, 3,5‐di‐ tert ‐butyl‐4‐bromopyrazole, 3,5‐di‐ tert ‐butyl‐4‐methylpyrazole, and 3,5‐diphenylpyrazole . A search in the CSD (version 5.38; 2017+3 updates) did not reveal any type of peroxido complex in which the coordination sphere contains a single N,N‐chelated pyrazole or triazole of any kind.…”

Activation of molecular oxygen by a molybdenum complex for catalytic oxidation

“…In the course of our ongoing research on high-valent molybdenum-oxo complexes bearing Schiff-base ligands and their reactivity in OAT reactions, [15][16][17] we report herein the synthesis and characterization of a new molybdenum(VI) dioxo complex which can be reduced and subsequently activate dioxygen to form a new molybdenum(VI) oxo-peroxo complex. This activation proceeds via the formation of a five-coordinated molybdenum(IV) mono-oxo complex or a highly unusual trans-[MoO(PMe) 3 ] 2+ intermediate which was characterized by NMR spectroscopy and elemental analysis.…”