Synthesis and characterization of 17-valence-electron [CpCr(NO)X2]- anions: oxidatively induced loss of the nitrosyl ligand

Anionic and paramagnetic [CpCr(NO)X2]- complexes were synthesized by the reaction of [NBu4]I with [CpCr(NO)I]2. The CpCr(NO)X2 anions exhibited single strong nitrosyl-stretching absorption that was generated by a linear nitrosyl group. The formation of CpCr(NO)Cl2 from the oxidation of [CpCr(NO)Cl2]- also involved the formation of an initial oxidation product that was unstable due to the loss of the NO unit. Furthermore, the stability of the anionic and paramagnetic complexes were dependent on pi-donation from alkoxide or amide ligands which reinforced the low-spin state.