The iron catalyst refers to an elemental iron or iron compound which has a catalytic function. Iron is a white or silvery white metal. Iron is a good reducing agent and is chemically active. At room temperature, iron does not readily react with other substances in dry air. Iron containing impurities is easily corroded in humid air. At high temperatures, iron burns violently in oxygen to form Fe3O4. Iron is widely distributed, accounting for 4.75% of the earth's crust. The valence of iron has 0, +2 , +3 and +6 . The valence of iron in most iron catalysts is 0, +2 or +3. Elemental iron and some iron compounds (such as iron oxide and carbonyl iron) have good catalysis and can catalyze some specific reactions.
Iron has the characteristics of abundant reserves, low cost and low toxicity, and various valence states. Therefore, iron catalyst is an ideal catalyst. Due to its high catalytic activity, high selectivity and environmental protection, iron catalysts have a wide range of applications in the field of organic synthesis and environmental protection.
- Polymerization: Polyolefins are widely used in people's daily life, and olefins can be prepared into polyolefins by polymerization. The iron complex can be used as a catalyst for the polymerization reaction. For example, the 2,6-diarylamidopyridine iron (II) complex can be used as a catalyst to catalyze the polymerization of acetylene, while the bispyridine diimine iron complex can catalyze the polymerization of olefin. When the iron complex is used as a catalyst to catalyze the polymerization, it has good thermal stability, high catalytic activity, low catalyst dosage, and long catalytic life. In addition, a product having a high degree of polymerization can be obtained in the catalytic process.
Figure 1. Iron catalyst catalyzed polymerization
- Hydrogenation reaction: Asymmetric hydrosilation/borohydride reactions can be used to synthesize chiral compounds such as chiral alcohols, amines and silanes. Carbonyl ironl is one of the most stable and inexpensive Fe(0) compounds. Since the carbonyl iron complex can be partially dissociated under certain conditions to produce an active site, it can be used as a catalyst for the hydrogenation reaction. The mechanism of the catalytic hydrogenation of carbonyl iron is that the zero-valent iron catalyst activates H2 by oxidative addition to produce a ferrous iron-negative hydrogen intermediate, and then undergoes subsequent steps such as insertion and reduction elimination to complete the catalytic cycle. The carbonyl iron catalyst can catalyze the asymmetric hydroboration of olefins, the asymmetric hydrosilylation of olefins, and the hydrosilylation of ketones.
Figure 2. Iron catalyst catalyzed hydrogenation reaction
- Coupling reaction: Transition metal catalyzed coupling reactions are an important means of constructing carbon-carbon bonds. Iron is an ideal transition metal catalyst due to its abundant reserves. The coupling reaction catalyzed by iron catalyst includes the coupling reaction of halogenated hydrocarbon with metal reagent, oxidative coupling reaction and reduction coupling reaction. In addition, the iron catalyst can catalyze the C-H direct functional grouping reaction to construct a carbon-carbon bond.
Figure 3. Iron catalyst catalyzed coupling reaction
- Cycloaddition reaction: The cycloaddition reaction can simultaneously construct multiple chemical bonds in one step, and it's one of the most popular fields in organic synthesis. Iron catalysts can catalyze a variety of cycloaddition reactions, including asymmetric [3+2] cycloaddition reactions, asymmetric [3+3] cycloaddition reactions, and [2+2+2] cycloaddition reactions. The iron catalyst has good catalytic activity in the catalytic cycloaddition reaction. In addition, high stereoselectivity and high enantioselectivity can be achieved by using different iron catalysts.
- Other reactions: In addition to the above reactions, the iron catalyst can catalyze many other reactions in organic synthesis. For example, iron catalysis can catalyze an asymmetric conjugate addition reaction of an ɑ,β-unsaturated carbonyl compound for the preparation of natural products and physiologically active drugs or intermediates. Iron catalysis can catalyze the amination of aryl halohydrocarbons/aromatics under mild conditions. In addition, iron catalysis can also catalyze N-methylation, chlorination of toluene, and elimination of alcohol.
- Environmental protection: In the field of environmental protection, iron catalysts also have important applications. Iron phosphate has unique catalytic properties and can be used as a catalyst for photocatalytic reactions to degrade industrial wastewater and domestic sewage.
- Liu, Wei. (2019). "Iron-Catalyzed Intramolecular Amination of Aliphatic C-H Bonds of Sulfamate Esters with High Reactivity and Chemoselectivity." Organic Letters 21(8), 2673
- Derdour, Karima. (2018), " Removal of Cr(VI) from aqueous solutions by using activated carbon supported iron catalysts as efficient adsorbents." World Journal of Engineering 15(1), 3-13.
- Hu, Meng-Yang. (2019), "Iron-Catalyzed Dihydrosilylation of Alkynes: Efficient Access to Geminal Bis(silanes)" Journal of the American Chemical Society 141(11), 4579-4583.
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