57034-48-7Relevant articles and documents
Syntheses and properties of anionic and neutral radical complexes containing CpM(NO)2 groups (M = Cr, Mo, or W)
Legzdins, Peter,Wassink, Berend
, p. 482 - 493 (2008/10/08)
The reduction behavior of a series of organometallic complexes containing CpM(NO)2 groups (Cp = η5-C5H5; M = Cr, Mo, or W) has been investigated by both cyclic voltammetry and chemical means. In general, neutral 18-electron CpM(NO)2Y compounds (Y = Me, Et, H, D, or Cl) undergo a single, essentially reversible, one-electron reduction in CH2Cl2/0.1 M [n-Bu4N]PF6. E1/2 values range from -0.62 to -1.01 V vs SCE, varying linearly with the νNO's of the CpM(NO)2Y reactant, and the ease of reduction increases with M as Cr 2Me which is the most difficult to reduce and exhibits two reduction waves in its cyclic voltammogram with peak potentials being dependent on scan rates. The electrochemically observed reductions can be effected on a preparative scale by employing Cp2Co as the chemical reductant, and the [Cp2Co][CpM(NO)2Y] (M ≠ Cr, Y ≠ Me) products are isolable in good yields as air- and temperature-sensitive solids. The stability of these products decreases in the order Y = Me ? Et > H ? D > Cl. IR and ESR spectra of the 19-electron [CpM(NO)2Y]?- radical anions are consistent with the anions possessing three-legged piano-stool molecular structures with linear, terminal nitrosyl ligands. Furthermore, they indicate considerable delocalization of the unpaired electron onto these nitrosyl ligands via M→NO back-bonding. The radical anions are cleanly reconverted to their neutral precursors by treatment with chemical oxidants such as AgBF4 or [Cp2Fe]BF4. In a complementary manner, the 18-electron cations of [CpM(NO)2L]+BF4- salts (M = Mo or W; L = PPh3 or P(OMe)3) undergo facile, one-electron reversible reductions in CH2Cl2, E1/2 being ～0.1 V vs SCE. Consequently, treatment of the salts with Cp2Co in CH2Cl2 affords isolable [CpM(NO)2L]? 19-electron, neutral radicals whose spectroscopic properties again reveal that their HOMO's are largely NO-based π* molecular orbitals. This delocalization of electron density evidently stabilizes all the CpM(NO)2-containing reduced species with respect to undergoing bond ruptures upon electron addition.
