Syntheses, structures, and NMR spectroscopy of paramagnetic open vanadocenes and open chromocenes

The syntheses and characterizations of the M[1,5-(Me3Si)(2)C5H5](2) complexes for M = V and Cr have been achieved, as well as that for the unsymmetric Cr[1-Me3Si-3-MeC5H5](2). Structural data for the vanadium complex reveal substantial steric crowding, in accord with the observation that this complex is only weakly coordinated by CO. Structural data have also been determined for Cr(C5H5)(2,4-C7H11) (C7H11 = dimethylpentadienyl), revealing the presence of both eclipsed and staggered conformations in the solid state and much shorter Cr-C bonds for the open dienyl ligand. Proton NMR spectra have been recorded for these and related paramagnetic complexes. While one observes relatively narrow signals and small upfield shifts for methyl and silyl substituents in the chromium complexes, much broader signals and greater shifts, downfield, are observed for hydrogen substituents; furthermore, these resonances are substantially broadened relative to those in chromocene. For V(2,4C(7)H(11))(2), the broadening is so great that only the methyl signals can be assigned with certainty.