The influence of reversible trianionic pincer OCO³⁻μ-oxo Cr^ivdimer formation ([Cr^iv]₂(μ-O)) and donor ligands in oxygen-atom-transfer (OAT)

Abstract

The oxygen-atom-transfer (OAT) from [(t)BuOCO]Cr(V)(O)(THF) (2) (where (t)BuOCO = [2,6-C(6)H(3)(6-(t)BuC(6)H(3)O)(2)](3-), THF = tetrahydrofuran) to triphenylphosphine (PPh(3)) in THF produces [(t)BuOCO]Cr(III)(THF)(3) (1) and triphenylphosphine oxide (OPPh(3)) at a rate of 69.5(±1.9) M(-1) s(-1) (22 °C). Identical rate constants were attained when acetonitrile (MeCN) and dichloromethane/THF (CH(2)Cl(2)/THF) were used as solvents. Electron paramagnetic resonance (EPR) data shows that the six-coordinate complex, [(t)BuOCO]Cr(V)(O)(THF)(2) (2a) forms upon addition of THF to 2, suggesting 2a as the active OAT species in THF. Similarly, addition of OPPh(3) has no influence on the rate of OAT, but the addition of triphenylphosphorus ylide (CH(2)PPh(3)) to form [(t)BuOCO]Cr(V)(O)(CH(2)PPh(3)) (4) prevents OAT to PPh(3). In CH(2)Cl(2), a [Cr(IV)](2)(μ-O) intermediate forms during the OAT from 2 to PPh(3). The OAT from {[(t)BuOCO]Cr(IV)(THF)}(2)(μ-O) (3) to PPh(3) reveals a zero-order dependence in PPh(3) indicating the dimer must first dissociate prior to OAT. The decay of 3versus time does not follow first-order kinetics due to the formation of a [(t)BuOCO]Cr(III)(THF) species (5) that inhibits the dissociation of 3. The change in concentration of 3versus time during OAT was simulated to obtain approximate rate constants.

Synthesis, Characterization, and Reactivity of Iron(III) Complexes Supported by a Trianionic ONO3– Pincer Ligand

“…Complex 5·H 2 O comprises a distorted octahedral Fe(III) ion coordinated by the [CF 3 −ONO] 3− pincer-type ligand, a bidentate 2,2′-bipyridine, and a H 2 O molecule. The main distortion from an ideal octahedral geometry is the acute angle (74.50 (6) 15 (125.50(7)°) also exhibit small bite angles and feature a pincer ligand spanning the equatorial sites of a trigonal bipyramid instead of the most commonly observed orientation of meridional coordination within a square pyramid or octahedral complex.…”

New Alkylidyne Complexes Featuring a Flexible Trianionic ONO3– Pincer-Type Ligand: Inorganic Enamine Effect versus Sterics in Electrophilic Additions

“…At 0.09, the Addison parameter 47 τ is consistent with a square-pyramidal geometry. Around the nitrogen atom, the sum of angles measures 339.64 (14)°, indicating pyramidalization, and again, the proton was refined freely (N1−H1 = 0.82(2) Å). Consistent with 1D-NOE data (see Figure S43 in the Supporting Information), the proton on the nitrogen adopts an anti configuration with respect to the alkylidyne fragment.…”

Compelling mechanistic data and identification of the active species in tungsten-catalyzed alkyne polymerizations: conversion of a trianionic pincer into a new tetraanionic pincer-type ligand

“…48 The notion was that trianionic pincer ligands should be capable of supporting highoxidation state metal complexes bearing M-X multiple bonds and vacant coordination sites (X ¼ N, O, C). [49][50][51][52][53][54][55] These ligands conne three anionic donors to a meridional plane, [56][57][58][59] and thus provide the necessary space for incoming alkyne substrates to interact with the metal center. 48 Our approach to creating a coordinatively unsaturated species for highly active alkyne polymerization catalysts seemed correct; however, the unusually high activity of 1 as a precatalyst is not derived from the presence of a trianionic pincer ligand, but rather the in situ formation of a complex featuring a novel tetraanionic pincer-alkylidene ligand [O 2 C(R)C]] 4À , where R ¼ Ph, and t Bu (Fig.…”