Mono- and Dimeric Phosphine Complexes of Cyclopentadienylvanadium(II) Halides

Reduction of CpVX2(PR3)2 (X = Cl, R = Me, Et; X = Br, R = Et) with Al or Zn in THF gives dimeric vanadium(II) complexes [CpVX(PR3)]2. Methylcyclopentadienyl compounds are accessible by the same method. Treating the dimers with an excess of PR3 gives CpVx(PR3)2, and treating the dimers with bidentate phosphines, CpVCl(DMPE) and CpVCl(DPPE) are obtained. All compounds are paramagnetic with, in principle, three unpaired electrons on the metal atom. 1H NMR spectra of the complexes show large downfield shifts of the cyclopentadienyl protons (range of 64-250 ppm). The phosphine ligands show smaller shifts, varying between -3.0 and 4.60 ppm for the dimers [CpVX(PR3)], and between -25.5 and -17.0 ppm for CpVCl(DMPE). The complexes are very reactive and their reactions with a variety of substrates, e.g., dioxygen, cyclohexene oxide, alkynes, and carbon monoxide, proceed easily. With α-olefins no reaction (hydrogenation, isomerization, or oligomerization) was observed