Chromium(III) and Chromium(II) Phenolate Complexes with Bulky Alkylcyclopentadienyl Ligands

Smytschkow, Igor; Gidt, Wjatscheslaw; Kunz, Christoph; Sun, Yu; Langer, Jens; Oelkers, Benjamin; Böttcher, Tobias; Sitzmann, Helmut

doi:10.1002/ejic.201900275

Cited by 5 publications

(2 citation statements)

References 41 publications

(41 reference statements)

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“…In Cr/LTO , the local environment of chromium has a trigonal bipyramidal structure with a coordination number of five. − This includes a Cr–C bond (2.034 Å), two Cr–O bonds (1.940 and 1.944 Å) where the oxygen atoms originate from terminal hydroxyl groups, and two Cr–O bonds (1.944 and 2.271 Å) resulting from interactions with lattice oxygen atoms from the LTO support. Similar five-coordinate chromium(II) complexes exhibiting trigonal bipyramidal geometry have been previously reported but are generally uncommon. − …”

Section: Resultssupporting

confidence: 74%

Supported Organochromium Ethylene Oligomerization Enabled by Surface Lithiation

Kanbur,

Hall,

Kim

et al. 2024

ACS Catal.

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In this work, supported organochromium ethylene polymerization catalysts have been tuned to mediate ethylene oligomerization via surface lithiation, which provides a generalizable protocol to control stereoelectronics and redox states of surface organometallic active sites. The homoleptic chromium(IV) alkyl complex Cr(CH 2 SiMe 3 ) 4 was grafted on high-surface-area anatase titania (TiO 2 ) nanoparticles as well as on silica to produce Cr/TiO 2 and Cr/SiO 2 , respectively. Treatment of these materials with excess n-butyllithium led to the reduced chromium complexes Cr/Li x TiO 2 and Cr/Li/SiO 2 , each of which still retains one hydrocarbyl ligand on chromium. A set of heterogeneous complexes were studied by electron paramagnetic resonance and X-ray absorption spectroscopy, which indicate a reduction in the oxidation state of the major chromium species to Cr II upon lithiation. Cr/ Li x TiO 2 converts ethylene to hexenes with a high selectivity (>80%), which was persistent over 10 days at 80 °C, achieving >950 turnovers. The exclusive formation of C 4 and C 6 olefins, preferring the trimerization product, without a statistical (Flory−Schulz) distribution is characteristic of the oxidative cyclization oligomerization mechanism rather than the traditional Cossee−Arlman mechanism, whereas Cr/Li/SiO 2 produced a mixture of trimerization and polymerization products, suggesting site heterogeneity in the silica-based material. On the other hand, the unreduced chromium(IV) materials as well as low lithium-containing Cr/Li x TiO 2 (x < 0.16) exclusively produced ultrahigh molecular weight polyethylene, determined by differential scanning calorimetry and gel permeation chromatography analysis, likely formed via a linear-insertion mechanism, with a crossover from the polymerization to oligomerization regime observed at ∼16% Li intercalation.

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Section: Resultssupporting

confidence: 74%

Supported Organochromium Ethylene Oligomerization Enabled by Surface Lithiation

Kanbur,

Hall,

Kim

et al. 2024

ACS Catal.

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“…To place these observations in more context, the M–CF 3 and M–CH 3 bond lengths in structurally related metal complexes are presented in Table . − In addition, average M–CF 3 and M–CH 3 bond lengths for elements that possess structurally characterized trifluoromethyl compounds are summarized in Table . Examination of these data indicate that the notion that M–CF 3 bonds are shorter than corresponding M–CH 3 bonds is not universally observed.…”

Section: Resultsmentioning

confidence: 99%

Organozinc Fluoride and Trifluoromethyl Compounds Supported by the Bis(2-pyridylthio)methyl Ligand

Shlian

Parkin

2022

Organometallics

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The bis(2-pyridylthio)methyl ligand, [Bptm], has been employed in the synthesis of {[Bptm]Zn(μ-F)} 2 , a rare example of an organozinc fluoride compound. The dimeric nature of {[Bptm]Zn(μ-F)} 2 , which possesses an uncommon [Zn(μ-F)] 2 motif, contrasts with the monomeric structures reported for the other halide derivatives, [Bptm]ZnX (X = Cl, Br, I); this difference is supported by density functional theory calculations which indicate that the fluoride derivative favors a dimeric form with bridging fluoride ligands, whereas the other derivatives favor monomeric structures with terminal halide ligands. {[Bptm]Zn(μ-F)} 2 reacts with Me 3 SiCF 3 to afford the organozinc trifluoromethyl complex, namely [Bptm]ZnCF 3 . The Zn−CF 3 bond in this complex is longer than the Zn−CH 3 bond of the previously reported methyl derivative [Bptm]ZnMe, an observation that is precedented in related zinc compounds but counter to other metal complexes. The infrared frequency corresponding to the asymmetric C−F stretch of [Bptm]ZnCF 3 is unusually low for a metal trifluoromethyl species but is comparable to those for other zinc and cadmium complexes.

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