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Keywords:

  • Molybdenum;
  • N ligands;
  • Nitrogen fixation;
  • Supported catalysts;
  • Immobilization

Abstract

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.