Four-Legged Piano Stool Molybdenum(II) Compounds without Carbonyl Ligands. 4. Cyclopentadienylmolybdenum(II) Complexes with 16-Electron and 18-Electron Configurations

Monocyclopentadienyl complexes of Mo(II) with 16- and 18-electron configurations of the form (Ring)MoClL x ( x = 2, Ring = Cp, L = PMe 2 Ph; x = 2, Ring = Cp*, L = PMe 3, PMe 2 Ph, L 2 = dppe; x = 3, Ring = Cp, L = PMe 2 Ph) are described. All of the 16-electron complexes are paramagnetic with an S = 1 ground state, as shown by magnetic measurements in the solid state and in solution, and by the contact-shifted 1 H NMR spectra. The structure of Cp*MoCl(dppe) was determined by X-ray diffraction methods. The 18-electron complex CpMoCl(PMe 2 Ph) 3 has been synthesized by reduction of {CpMoCl 2 } n with Na in the presence of 3 equiv of phosphine. It has been fully characterized by 1 H and 31 P NMR, chemical analysis, and X-ray structural determination. Thermolysis of a THF or C 6 D 6 solution of this 18-electron species generates the 16-electron paramagnetic Mo(II) complex CpMoCl(PMe 2 Ph) 2 . The Cp*MoClL 2 (L = PMe 3 and PMe 2 Ph) systems react with 2-electron-donor ligands, i.e. CO and H 2, to afford stable 18-electron complexes. The carbonyl derivative Cp*MoCl(CO)(PMe 2 Ph) 2 has also been characterized by X-ray crystallography.