Synthesis, reactivity, and structure of strictly homologous 18 and 19 valence electron iron nitrosyl complexes

The 18 and 19 valence electron (VE) nitrosyl complexes [Fe(NO)-('pyS(4)') ( [1]BF4) and [Fe(NO)-('pyS4')] (2) have been synthesized from [Fe('pyS(4)')] x ('pyS(4)'(2-) = 2,6-bis-(2-mercaptophenylthiomethyl)pyridine-(2-)) and ei ther NOBF4 or NO gas. Complex [1]BF, was also obtained from [Fe(CO)('pyS(4) ')] and NOBF4. The cation [1]- is reversibly reduced to give 2. Oxidation o f 2 by [Cp2Fe]PF6 afforded [Fe(NO)('pyS(4)')]PF6 ([1]PF6). The molecular st ructures of [1]PF6 and 2 were electron to [1](-) causes a significant elong ation of the Fe-donor atom bonds and a bending of the FeNO angle. Density f unctional calculations show that the unpaired electron in 2 occupies determ ined by X-ray crystallography. They demonstrate that addition of one electr on to [1] causes a significant an orbital. which is antibonding with respec t to all Fe-ligand interactions. As expected from qualitative Molecular Orb ital (MO) theory, it has a large contribution from a pi* type NO orbital. T he v(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 r eady reaction of 2 with excess NO to give [Fe(NO)(2)('py(S)')] (3), the fac ile NO/CO exchange of 2 to afford [Fe(CO)-('pyS(4)')], and the easy oxidati on of 2 to [1](-).