Synthesis, Characterization, and Ligand Rearrangement of Tungsten Cyclopropyl Complexes

In an effort to study the β-H abstraction/1,3-addition mechanism for CH bond activation, the syntheses of tungsten organometallic complexes featuring a cyclopropyl ligand were undertaken. Attempts to prepare the chloro cyclopropyl complex Cp*W­(NO)­Cl­(<i>c</i>-C₃H₅) instead afforded the previously reported allyl complex Cp*W­(NO)­Cl­(η³-CH₂CHCH₂), due to a ring-opening rearrangement of the cyclopropyl ligand. The alkyl cyclopropyl complex Cp*W­(NO)­(CH₂SiMe₃)­(<i>c</i>-C₃H₅) (<b>1</b>_<b>TMS</b>) was prepared and characterized in solution via NMR spectroscopy but also undergoes a ligand rearrangement process to afford the allyl complex Cp*W­(NO)­(CH₂SiMe₃)­(η³<i>-</i>CH₂CHCH₂) (<b>2</b>_<b>TMS</b>), which was characterized by NMR spectroscopy and an X-ray diffraction study. Attempts to inhibit the ligand rearrangement or isolate <b>1</b>_<b>TMS</b> in the solid state have been unsuccessful. In order to investigate the mechanism of the conversion of <b>1</b>_<b>TMS</b> to <b>2</b>_<b>TMS</b>, a kinetic study was undertaken, and some preliminary results are discussed