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

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• 作者：K. Cory MacLeod ; Brian O. Patrick ; Kevin M. Smith
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：January 2, 2012
• 年：2012
• 卷：51
• 期：1
• 页码：688-700
• 全文大小：620K
• 年卷期：v.51,no.1(January 2, 2012)
• ISSN：1520-510X

文摘

Oxidation of CpCr[(XylNCMe)₂CH] (Xyl = 2,6-Me₂C₆H₃) with pyridine N-oxide or air generated the 渭-oxo dimer, {CpCr[(XylNCMe)₂CH]}₂(渭-O). The 渭-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鈥搗is 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 纬-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鈥揌 bond followed by intermolecular C鈥揅 bond formation. The use of very bulky hexaisopropylterphenyl ligand substituents did not preclude the formation of the analogous 渭-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 渭-oxo dimer were used to improve the previously reported Cr-catalyzed radical cyclization of a bromoacetal.