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General Synthesis of Cyclopentadienylchromium(II) η 3 -Allyl Dicarbonyl Complexes

2004; American Chemical Society; Volume: 23; Issue: 9 Linguagem: Inglês

10.1021/om030690q

1520-6041

David W. Norman, Michael J. Ferguson, Jeffrey M. Stryker,

Synthetic Organic Chemistry Methods

Thermally stable chromium(II) dicarbonyl complexes bearing substituted η3-allyl and η5-cyclopentadienyl ligands have been prepared via oxidative addition of the allyl bromide to tris(acetonitrile)tricarbonylchromium at −30 °C in acetonitrile, followed by in situ addition of the ancillary cyclopentadienyl ligand anion at low temperature. Spectroscopic data for allyl complexes 1, 2, and 4−7 indicate that the solution configuration of the allyl ligand is preferentially exo, while the data for the 2-methylallyl derivative 3 suggest the formation of a 65:35 mixture of endo and exo isomers. The cyclohexenyl and indenyl complexes 5 and 7, respectively, exhibit interesting spectroscopic and structural characteristics. While most complexes were prepared in good yield, the addition of sterically larger ancillary ligands was problematic: the addition of indenyllithium led to low yields of the allylchromium complex, while treatment with (pentamethylcyclopentadienyl)lithium led to the isolation of only organic products. These diminished returns are attributed to attack of the ancillary ligand anion directly on the coordinated allyl ligand of the intermediate formed by oxidative addition. Solid-state structures of the η3-allyl, crotyl, and cyclohexenyl complexes, all in the exo configuration, have been determined by X-ray crystallography.