| Summary: | Reaction of [CpCr(NO)I]₂ with an excess of ammonia or allylamine yields the complex
salts [CpCr(NO)L₂]⁺[I]⁻ (L = NH₃, NH₂C₃H₅) . Heating these salts results in loss of L and
formation of the neutral complexes, CpCr(NO)(L)I. In contrast, reaction of [CpCr(NO)I]₂ with
the bulkier amine NH₂CMe₃ affords CpCr(NO)(lS[NH₂CMe₃)I directly. Sequential reaction of
CpCr(NO)( NH₂CMe₃)I or CpCr(NO)(P{OMe}3)I with AgPF₆ and further L affords,
respectively, the salts [CpCr(NO)(L)₂]⁺[PF₆]⁻(L = NH₂CMe₃, L = P(OMe)₃). All these species
exhibit room-temperature ESR spectra and magnetic moments consistent with their possessing
17-valence-electron configurations. Abstraction of a proton from the amine ligand of
[CpCr(NO)L₂]+ and CpCr(NO)(L)I (L = amine) compounds results in the formation of amidebridged
dimers [CpCr(NO)(NHR)]₂, which exist as mixtures of various cis- and /raws-isomers.
Reduction of [CpCr(NO)(NH₃)₂]⁺ to an 18-electron configuration results in loss ofNH₃,
so that CpCr(NO)(CO)₂ s formed in the presence of CO. In a reverse manner, oxidation of
CpCr(NO)(CO)₂ in acetonitrile produces [CpCr(NO)(NCMe)₂]⁺[PF₆]-. These observations
suggest that for CpCr(NO)L₂ complexes, a-basic ligands stabilize the 17-electron configurations
of cations whereas π-acidic ligands stabilize the 18-electron configurations of the neutral
congeners. This trend can be rationalized by the results of an Extended Hiickel molecular orbital
analysis of the CpCr(NO) fragment and the interaction of its frontier orbitals with those of various
ligands, L.
[more abstract available; see pdf]
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