Details

Autor(en) / Beteiligte

• MacLeod, K. Cory
• Patrick, Brian O
• Smith, Kevin M

Titel

Reactivity of Cr(III) μ-Oxo Compounds: Catalyst Regeneration and Atom Transfer Processes

Ist Teil von

• Inorganic chemistry, 2012-01, Vol.51 (1), p.688-700

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2012

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Oxidation of CpCr[(XylNCMe)2CH] (Xyl = 2,6-Me2C6H3) with pyridine N-oxide or air generated the μ-oxo dimer, {CpCr[(XylNCMe)2CH]}2(μ-O). The μ-oxo dimer was converted to paramagnetic Cr(III) CpCr[(XylNCMe)2CH](X) complexes (X = OH, O2CPh, Cl, OTs) via protonolysis reactions. The related Cr(III) alkoxide complexes (X = OCMe3, OCMe2Ph) were prepared by salt metathesis and characterized by single crystal X-ray diffraction. The interconversion of the Cr(III) complexes and their reduction back to Cr(II) with Mn powder were monitored using UV–vis spectroscopy. The related CpCr[(DepNCMe)2CH] (Dep = 2,6-Et2C6H3) Cr(II) complex was studied for catalytic oxygen atom transfer reactions with PPh3 using O2 or air. Both Cr(II) complexes reacted with pyridine N-oxide and γ-terpinene to give the corresponding Cr(III) hydroxide complexes. When CpCr[(DepNCMe)2CH] was treated with pyridine N-oxide in benzene in the absence of hydrogen atom donors, a dimeric Cr(III) hydroxide product was isolated and structurally characterized, apparently resulting from intramolecular hydrogen atom abstraction of a secondary benzylic ligand C–H bond followed by intermolecular C–C bond formation. The use of very bulky hexaisopropylterphenyl ligand substituents did not preclude the formation of the analogous μ-oxo dimer, which was characterized by X-ray diffraction. Attempts to develop a chromium-catalyzed intermolecular hydrogen atom transfer process based on these reactions were unsuccessful. The protonolysis and reduction reactions of the μ-oxo dimer were used to improve the previously reported Cr-catalyzed radical cyclization of a bromoacetal.