Synthesis and Catalytic Properties in Olefin Epoxidation of Novel Iron(II) Complexes with Pyridine-Containing Macrocycles Bearing an Aminopropyl Pendant Arm

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• 作者：Sonia Taktak ; Wanhua Ye ; Aida M. Herrera ; Elena V. Rybak-Akimova
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：April 2, 2007
• 年：2007
• 卷：46
• 期：7
• 页码：2929 - 2942
• 全文大小：210K
• 年卷期：v.46,no.7(April 2, 2007)
• ISSN：1520-510X

文摘

Three novel iron(II) complexes with pyridine-containing macrocycles bearing an aminopropyl pendant arm weresynthesized and characterized. Crystal structures of two of the complexes revealed high-spin iron(II) centerscoordinated to the five ligand nitrogen atoms with no coordination of either the solvent molecules or anions, resultingin an unusual square-pyramidal geometry. Related tetradentate ligand CRH formed a low-spin iron(II) complex(meso form was structurally characterized) with a planar arrangement of the four nitrogen atoms from the macrocycleand two axial acetonitrile molecules. Similarly to the corresponding nickel and copper complexes of the pentadentateligands, the protonation of the amino group on the ligand arm in iron(II) complexes was found to be reversible.Spectral changes and magnetic susceptibility measurements indicated that a change in the geometry and spinstate of the metal center is associated with this acid-base process. In the presence of noncoordinating acids (e.g.,triflic acid), these complexes, as well as their nonmethylated analogue, can efficiently catalyze the epoxidation ofcyclooctene and 1-decene under mild conditions, using hydrogen peroxide as the oxidant. However, in thedeprotonated form or in the presence of coordinating acids like HCl, no epoxidation occurs.