SYNTHESIS AND CHARACTERIZATION OF 17-VALENCE-ELECTRON [CPCR(NO)X-2](-) ANIONS - OXIDATIVELY INDUCED LOSS OF THE NITROSYL LIGAND

Several anionic and paramagnetic [CpCr(NO)X-2](-) complexes (X = I [1] , O3SCF3 (OTf) [2], Br [3], Cl [4]) have been prepared as potential pr ecursors to neutral CpCr(NO)X-2 species. Reaction of [CpCr(NO)I](2) wi th [NBu4]I provides [NBu4][1], and halide abstraction from [NBu4][1] w ith 2 equiv of AgOTf affords [NBu4][2]. The weakly-bound OTf- ligands of [NBu4][2] are readily displaced by Br- to produce [NBu4][3]. The di chloro complexes [NEt4][4] and [PPN][4] are obtained by treating [CpCr (NO)Cl](2) with [NE4]Cl and [PPN]Cl, respectively. Use of acetonitrile as reaction solvent allows generation of the requisite [CpCr(NO)Cl](2 ) directly from CpCr(NO)(CO)(2) and PCl5, a marked improvement over pr evious synthetic routes to this dimer. Similar halogenations of CpCr( NO)(CO)(2) in NCMe provide access to the previously unknown [CpCr(NO) I](2) (5), and [CpCr(NO)Cl](2) (6), halo-bridged, and dimers. The sol id-state molecular structure of [PPN][4]. CH2Cl2 has been established by single-crystal X-ray crystallography to be a normal three-legged pi ano stool. The one-electron oxidation of [4] has been investigated bot h chemically (by reaction with [Cp2Fe](+)) and electrochemically (by c yclic voltammetry). These studies suggest that upon oxidation a high-s pin CpCr(NO)Cl-2 complex is initially formed which then rapidly releas es NO. Extended Huckel molecular-orbital calculations have been perfor med on [4], [CpCr(CO)(3)](-), and [CpCrCl3](-), three CpCr-containing anions with ligands of varying pi-bonding capabilities. Correlations b etween their orbital energies and electron occupancies and a rationale for the lability of the NO ligand in neutral CpCr(NO)Cl-2 are provide d.