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Optimization of the Efficiency of Oxidation Catalysts Based on Iron Bispidine Complexes
Author(s) -
Comba Peter,
Wadepohl Hubert,
Wiesner Sebastian
Publication year - 2011
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201100212
Subject(s) - chemistry , catalysis , nonane , pyridine , styrene , medicinal chemistry , yield (engineering) , redox , catalytic oxidation , styrene oxide , polymer chemistry , inorganic chemistry , organic chemistry , copolymer , polymer , materials science , metallurgy
High‐valent bispidine iron‐oxo complexes are among the most efficient nonheme iron oxidation catalysts. Here, we report the synthesis and structural analysis of two derivatives of the known pentadentate bispidine ligand L 1 {L 1 = 2,4‐pyridyl‐7‐(pyridine‐2‐ylmethyl)‐3,7‐diazabicyclo[3.3.1]nonane}: L 2 and L 3 {L 2 = 2,4‐pyridyl‐7‐[1‐(pyridine‐2‐yl)ethyl]‐3,7‐diazabicyclo[3.3.1]nonane; L 3 = 2,4‐pyridyl‐7‐[phenyl(pyridine‐2‐yl)methyl]‐3,7‐diazabicyclo[3.3.1]nonane}, and of their Fe II complexes. The yield of the catalytic epoxidation of cyclooctene and styrene with iodosylbenzene as oxidant increases from the L 1 ‐ to the L 2 ‐ to the L 3 ‐based catalyst (e.g., the yield of styrene oxide, with MeCN as solvent, under anaerobic conditions, is 40 %, 90 %, 96 %, respectively), and this is correlated to the Fe III/II reduction potentials {[Fe(L 1 )(NCMe)] n + (1.01 V), [Fe(L 2 )(NCMe)] n + (1.13 V), and [Fe(L 3 )(NCMe)] n + (1.19 V), in MeCN, vs. SCE}. Although this correlation is not unexpected, the interpretation is not entirely trivial, and this is discussed in detail. The rigidity of the bispidine ligands and their preference for relatively large metal ions (low oxidation states, high spin multiplicities) is believed to be responsible for the efficiency of the bispidine‐based catalyst systems, and the present results show possible approaches to further improve the performance of these catalysts.