799267-43-9Relevant academic research and scientific papers
Studies of low-coordinate iron dinitrogen complexes
Smith, Jeremy M.,Sadique, Azwana R.,Cundari, Thomas R.,Rodgers, Kenton R.,Lukat-Rodgers, Gudrun,Lachicotte, Rene J.,Flaschenriem, Christine J.,Vela, Javier,Holland, Patrick L.
, p. 756 - 769 (2007/10/03)
Understanding the interaction of N2 with iron is relevant to the iron catalyst used in the Haber process and to possible roles of the FeMoco active site of nitrogenase. The work reported here uses synthetic compounds to evaluate the extent of NN weakening in low-coordinate iron complexes with an FeNNFe core. The steric effects, oxidation level, presence of alkali metals, and coordination number of the iron atoms are varied, to gain insight into the factors that weaken the NN bond. Diiron complexes with a bridging N2 ligand, LRFeNNFeLR (LR = β-diketiminate; R = Me, tBu), result from reduction of [LRFeCl]n under a dinitrogen atmosphere, and an iron(I) precursor of an N2 complex can be observed. X-ray crystallographic and resonance Raman data for LRFeNNFeLR show a reduction in the N-N bond order, and calculations (density functional and multireference) indicate that the bond weakening arises from cooperative back-bonding into the N2 π* orbitals. Increasing the coordination number of iron from three to four through binding of pyridines gives compounds with comparable N-N weakening, and both are substantially weakened relative to five-coordinate iron-N 2 complexes, even those with a lower oxidation state. Treatment of LRFeNNFeLR with KC8 gives K2L RFeNNFeLR, and calculations indicate that reduction of the iron and alkali metal coordination cooperatively weaken the N-N bond. The complexes LRFeNNFeLR react as iron(I) fragments, losing N2 to yield iron(I) phosphine, CO, and benzene complexes. They also reduce ketones and aldehydes to give the products of pinacol coupling. The K2LRFeNNFeLR compounds can be alkylated at iron, with loss of N2.
Reversible beta-hydrogen elimination of three-coordinate iron(II) alkyl complexes: Mechanistic and thermodynamic studies
Vela, Javier,Vaddadi, Sridhar,Cundari, Thomas R.,Smith, Jeremy M.,Gregory, Elizabeth A.,Lachicotte, Rene J.,Flaschenriem, Christine J.,Holland, Patrick L.
, p. 5226 - 5239 (2008/10/09)
High-spin organometallic complexes have not received extensive mechanistic study, despite their potential importance as unsaturated intermediates in catalytic transformations. We have found that, with a suitably bulky bidentate ligand, three-coordinate, high-spin alkyl complexes of iron(II) are stable. They undergo isomerization and exchange reactions of the alkyl group through β-hydride elimination and reinsertion, and the β-hydride elimination step is rate-limiting. The alkyl complexes transfer a β-hydrogen atom to C=C, C=N, and C=O double bonds and undergo deprotonation by Bronsted acids. The reversible β-hydride elimination reactions can be used to explore relative M-C bond energies. Competition experiments and density functional calculations demonstrate an enthalpic preference for alkyl isomers with iron bound to the terminal carbon of the alkyl fragment. This preference arises from steric and electronic effects. The steric preference could be overcome with a phenyl substituent, which steers iron to the benzylic position. A Hammett correlation and density functional calculations suggest that the substituent effect is attributable to resonance stabilization of partial negative charge on the alkyl ligand.
