Alkyl-for-iodide metathesis initiated by dissociation of the phosphine ligand from CpCr(NO)(PPh3)I

Article abstract of DOI:10.1021/ja00096a029

The alkyl-for-iodide metathesis reaction that occurs when CpCr(NO)(PPh₃)I (1) is treated with 2 equiv of Me₃SiCH₂MgCl in THF to form CpCr(NO)(PPh₃)(CH₂SiMe₃) (6) has been investigated in some detail. The conversion is initiated by loss of the phosphine ligand from the chromium atom's coordination sphere, the most compelling evidence for this step being that addition of excess phosphine (e.g. 4 equiv) to the initial reaction mixture completely inhibits the reaction. Four intermediate complexes which are formed sequentially on the reaction path from 1 to 6 have been detected by IR and ESR spectroscopy. These complexes have been identified as CpCr(NO)(THF)I (2), CpCr-(NO→Mg{CH₂SiMe₃}Cl)(THF)I (3), CpCr(NO→Mg{CH₂SiMe₃}Cl)(THF)(CH₂SiMe ₃) (4), and CpCr(NO)(THF)-(CH₂SiMe₃) (5). Complexes 3 and 4 have also been detected spectroscopically during the reaction of CpCr(NO)(THF)I (2) with Me₃SiCH₂MgCl which produces CpCr(NO)(THF)(CH₂SiMe₃) (5). This understanding of the mechanistic pathway has resulted in the development of a general synthetic route to previously inaccessible 17-valence-electron CpCr(NO)(L)R complexes (L = C₅H₁₁N or NH₂CMe₃, R = CH₂SiMe₃; L = C₅H₁₁N, R = CH₂Ph).