Proton and Electron Transfer to a Polymer-Supported Nitrido Molybdenum(VI) Complex


  • Dedicated to Professor Werner Uhl on the occasion of his 60th birthday


The protonation and reduction of nitrido and imido complexes are important steps during the reduction of dinitrogen to NH3 mediated by transition-metal complexes. A polymer-immobilized analogue (P-2) of the Schrock–Yandulov nitrido molybdenum(VI) complex has been prepared from a sterically unencumbered polymer-anchored triamidoamine ligand (P-1) and [MoCl3N(CH3CN)]4 as an “MoN” source. The polymer-confined nitrido complex has been protonated by [2,6-lutH][Al{OC(CF3)3}4] (2,6-lut = 2,6-lutidine) at the nitrido ligand to form the corresponding imido complex P-3, as shown by a variety of spectroscopic techniques and DFT calculations. Specifically, the NH stretching vibration of P-3 and the ND stretching vibration of the N-deuterated analogue P-3D as well as the vibrations of the counterion are particularly useful for unambiguous characterization. Single-electron transfer to the supported molybdenum(VI) complexes P-3/P-3D by cobaltocene as one-electron reductant gave the imido molybdenum(V) congeners P-4/P-4D as shown by diffuse reflectance UV/Vis (DR-UV/Vis) and IR spectroscopy in combination with DFT calculations. The electron paramagnetic resonance (EPR) spectra of the immobilized d1 complex P-4 and its deuterated isotopomer P-4D reveal spin density on the molybdenum center and the imido ligand. For comparison of their spectroscopic and reactivity properties, the analogous soluble ligand 1 and its nitrido (2) and imido (3) complexes have also been synthesized. Compounds 1 and 2 were also characterized by single-crystal X-ray diffraction.