Insertions of Electrophiles into Metal-Carbon Bonds: Formation of New Carbon-Nitrogen Linkages Mediated by the (ν5-Cyclopentadienyl)dinitrosylchromium Group

Article abstract of DOI:10.1021/ja00188a024

Electrophiles NE⁺ (E=O, p-O2NC6H4N, or S) undergo unprecedented insertions into the Cr-C ? bonds of CpCr(NO)2R complexes (Cp-η⁵-C5H5; R=Me, CH2SiMe3, or Ph) to afford ⁺ cationic complexes.Present evidence is consistent with these insertions occurring via charge-controlled, intramolecular attacks by NE⁺ at the Cr-R groups in classical S_E2 processes.When R=Me and E=O, the initially formed product isomerizes intramoleculary to the novel formaldoxime complex, ⁺, which is isolable as its PF₆^- salt.Single crystals of this salt and that resulting from the reaction of ⁺BF4^- with CpCr(NO)2Me have been subjected to X-ray crystallographic analyses. ⁺PF6^- crystallizes in the monoclinic space group P2₁/c with cell dimensions a=7.903 (3) Angstroem, b=12.192 (2) Angstroem, c=13.417 (5) Angstroem, β=95.59 (3) deg.Similarly, crystals of ⁺BF4^- are also monoclinic , space group P2₁/c, but with cell dimensions a=8.300 (1) Angstroem, b=16.964 (2) Angstroem, c=12.536 (2) Angstroem, and β=101.87 (1) deg.The structures of the complexes were refined to final R_F values of 0.045 and 0.054, respectively.The most chemically interesting feature of both molecular structures is that the newly formed formaldoxime and p-nitrophenylmethyldiazene ligands function as Lewis bases through nitrogen atoms toward the formally 16-electron ⁺ cations.These ligands may be displaced from the chromium's coordination sphere by the more strongly coordinating Cl^- anion.The resulting CpCr(NO)2Cl can be reconverterd to CpCr(NO)2R by treatment with the appropriate Grignard or organoaluminum reagent, thereby completing a cycle by regenerating the initial organometallic reactant.The entire sequence of stoichiometric reactions forming the cycle thus constitutes a selective method for the formation of new carbon-nitrogen bonds, the net organic conversions mediated by the CpCr(NO)2 group being NE⁺ + R^- -> N(E)R.