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A multi-iron system capable of rapid N2 formation and N2 cleavage.

MacLeod KC, Vinyard DJ, Holland PL - J. Am. Chem. Soc. (2014)

Bottom Line: Surprisingly, these mild reagents generate high yields of iron(I) products from the iron(II/III) starting material.This is the first molecular system that both breaks and forms the triple bond of N2 at room temperature.These results highlight the ability of multi-iron species to decrease the energy barriers associated with the activation of strong bonds.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States.

ABSTRACT
The six-electron oxidation of two nitrides to N2 is a key step of ammonia synthesis and decomposition reactions on surfaces. In molecular complexes, nitride coupling has been observed with terminal nitrides, but not with bridging nitride complexes that more closely resemble catalytically important surface species. Further, nitride coupling has not been reported in systems where the nitrides are derived from N2. Here, we show that a molecular diiron(II) diiron(III) bis(nitride) complex reacts with Lewis bases, leading to the rapid six-electron oxidation of two bridging nitrides to form N2. Surprisingly, these mild reagents generate high yields of iron(I) products from the iron(II/III) starting material. This is the first molecular system that both breaks and forms the triple bond of N2 at room temperature. These results highlight the ability of multi-iron species to decrease the energy barriers associated with the activation of strong bonds.

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ORTEP diagrams of the X-ray crystal structures of LFe(CNXyl)3 (3, left) and LFe(CO)3 (4, right) using 50% thermal ellipsoids. The xylyl groups on the isocyanidesin 3 are omitted for clarity.
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fig1: ORTEP diagrams of the X-ray crystal structures of LFe(CNXyl)3 (3, left) and LFe(CO)3 (4, right) using 50% thermal ellipsoids. The xylyl groups on the isocyanidesin 3 are omitted for clarity.

Mentions: To our knowledge, there is only one reported iron systemwherea nitride complex is generated from N2.4 Our group described a reaction sequence that started withreduction of LFeCl (L = bulky β-diketiminate ligand, shown inFigure 1) to the iron(I) oxidation level. Inthe presence of 1 atm N2, the N–N triple bond of N2 was cleaved to give two bridging nitridesin a tetranuclear complex that has two iron(II) ions and two iron(III)ions (1 in Scheme 1). Herein, we report the selective formation of N–Nbonds in the bis(nitride) complex to release the two bridging nitrideligands as N2 in high yield. This is the first demonstrationof N–N triple bond cleavage and N–N triple bond formationby a single homogeneous system. Both reactions occur at or below roomtemperature, indicating that the multi-iron active site greatly lowersthe kinetic barriers for N2 formation and cleavage.


A multi-iron system capable of rapid N2 formation and N2 cleavage.

MacLeod KC, Vinyard DJ, Holland PL - J. Am. Chem. Soc. (2014)

ORTEP diagrams of the X-ray crystal structures of LFe(CNXyl)3 (3, left) and LFe(CO)3 (4, right) using 50% thermal ellipsoids. The xylyl groups on the isocyanidesin 3 are omitted for clarity.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4353015&req=5

fig1: ORTEP diagrams of the X-ray crystal structures of LFe(CNXyl)3 (3, left) and LFe(CO)3 (4, right) using 50% thermal ellipsoids. The xylyl groups on the isocyanidesin 3 are omitted for clarity.
Mentions: To our knowledge, there is only one reported iron systemwherea nitride complex is generated from N2.4 Our group described a reaction sequence that started withreduction of LFeCl (L = bulky β-diketiminate ligand, shown inFigure 1) to the iron(I) oxidation level. Inthe presence of 1 atm N2, the N–N triple bond of N2 was cleaved to give two bridging nitridesin a tetranuclear complex that has two iron(II) ions and two iron(III)ions (1 in Scheme 1). Herein, we report the selective formation of N–Nbonds in the bis(nitride) complex to release the two bridging nitrideligands as N2 in high yield. This is the first demonstrationof N–N triple bond cleavage and N–N triple bond formationby a single homogeneous system. Both reactions occur at or below roomtemperature, indicating that the multi-iron active site greatly lowersthe kinetic barriers for N2 formation and cleavage.

Bottom Line: Surprisingly, these mild reagents generate high yields of iron(I) products from the iron(II/III) starting material.This is the first molecular system that both breaks and forms the triple bond of N2 at room temperature.These results highlight the ability of multi-iron species to decrease the energy barriers associated with the activation of strong bonds.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States.

ABSTRACT
The six-electron oxidation of two nitrides to N2 is a key step of ammonia synthesis and decomposition reactions on surfaces. In molecular complexes, nitride coupling has been observed with terminal nitrides, but not with bridging nitride complexes that more closely resemble catalytically important surface species. Further, nitride coupling has not been reported in systems where the nitrides are derived from N2. Here, we show that a molecular diiron(II) diiron(III) bis(nitride) complex reacts with Lewis bases, leading to the rapid six-electron oxidation of two bridging nitrides to form N2. Surprisingly, these mild reagents generate high yields of iron(I) products from the iron(II/III) starting material. This is the first molecular system that both breaks and forms the triple bond of N2 at room temperature. These results highlight the ability of multi-iron species to decrease the energy barriers associated with the activation of strong bonds.

Show MeSH