Synthesis, Reactivity, and Structure of Strictly Homologous 18 and 19 Valence Electron Iron Nitrosyl Complexes

• Published in: Chemistry : a European journal 2001-05, Vol.7 (9), p.1874-1880
• Main Authors: Sellmann, Dieter, Blum, Nicole, Heinemann, Frank W., Hess, Bernd A.
• Format: Article
• Language: English
• Subjects: density functional calculations; iron; nitrosyl complexes; S ligands; structure elucidation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20010504)7:9<1874::AID-CHEM1874>3.0.CO;2-2

The 18 and 19 valence electron (VE) nitrosyl complexes [Fe(NO)(′pyS4′)]BF4 ([1]BF4) and [Fe(NO)(′pyS4′)] (2) have been synthesized from [Fe(′pyS4′)]x (′pyS4′2−=2,6‐bis(2‐mercaptophenylthiomethyl)pyridine(2−)) and either NOBF4 or NO gas. Complex [1]BF4 was also obtained from [Fe(CO)(′pyS4′)] and NOBF4. The cation [1]+ is reversibly reduced to give 2. Oxidation of 2 by [Cp2Fe]PF6 afforded [Fe(NO)(′pyS4′)]PF6 ([1]PF6). The molecular structures of [1]PF6 and 2 were determined by X‐ray crystallography. They demonstrate that addition of one electron to [1]+ causes a significant elongation of the Fe‐donor atom bonds and a bending of the FeNO angle. Density functional calculations show that the unpaired electron in 2 occupies an orbital, which is antibonding with respect to all Fe‐ligand interactions. As expected from qualitative Molecular Orbital (MO) theory, it has a large contribution from a π* type NO orbital. The ν(NO) frequency decreases from 1893 cm−1 in [1]BF4 to 1648 cm−1 in 2 (in KBr). The antibonding character of the unpaired electron explains the ready reaction of 2 with excess NO to give [Fe(NO)2(′pyS4′)] (3), the facile NO/CO exchange of 2 to afford [Fe(CO)(′pyS4′)], and the easy oxidation of 2 to [1]+. Without precedent, the influence of one unpaired electron upon structure and reactivity could be elucidated by X‐ray crystallography and DFT calculations for strictly homologous 18 and 19 valence electron nitrosyl complexes with identical donor atom sets and connectivities. The complexes [Fe(NO)(′pyS4′)]+ ([1]+) and [Fe(NO)(′pyS4′)] (2) (see scheme) result from the reactions of [Fe(′pyS4′)]x with NOBF4 or NO gas and they are redox interconvertible.