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Synthesis and characterization of 17-valence-electron [CpCr(NO)X-2](-) anions: Oxidatively induced loss of the nitrosyl ligand

TitleSynthesis and characterization of 17-valence-electron [CpCr(NO)X-2](-) anions: Oxidatively induced loss of the nitrosyl ligand
Publication TypeJournal Article
Year of Publication1997
AuthorsLegzdins, P, McNeil, WS, Rettig, SJ, Smith, KM
JournalJournal of the American Chemical Society
Date PublishedApr
Type of ArticleReview
ISBN Number0002-7863

Several anionic and paramagnetic [CpCr(NO)X-2](-) complexes (X = I [1], O3SCF3 (OTf) [2], Br [3], Cl [4]) have been prepared as potential precursors to neutral CpCr(NO)X-2 species. Reaction of [CpCr(NO)I](2) with [NBu4]I provides [NBu4][1], and halide abstraction from [NBu4][1] with 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 dichloro 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 previous synthetic routes to this dimer. Similar halogenations of Cp*Cr(NO)(CO)(2) in NCMe provide access to the previously unknown [Cp*Cr(NO)I](2) (5), and [Cp*Cr(NO)Cl](2) (6), halo-bridged, and dimers. The solid-state molecular structure of [PPN][4]. CH2Cl2 has been established by single-crystal X-ray crystallography to be a normal three-legged piano stool. The one-electron oxidation of [4] has been investigated both chemically (by reaction with [Cp2Fe](+)) and electrochemically (by cyclic voltammetry). These studies suggest that upon oxidation a high-spin CpCr(NO)Cl-2 complex is initially formed which then rapidly releases NO. Extended Huckel molecular-orbital calculations have been performed on [4], [CpCr(CO)(3)](-), and [CpCrCl3](-), three CpCr-containing anions with ligands of varying pi-bonding capabilities. Correlations between their orbital energies and electron occupancies and a rationale for the lability of the NO ligand in neutral CpCr(NO)Cl-2 are provided.

URL<Go to ISI>://A1997WU27200013