SYNTHESIS AND CHARACTERIZATION OF TI, CR, MO AND W BIS(FLUORENE) COMPLEXES

The new eta(6)-bisfluorene complexes of Ti, Cr, Mo, and W were prepare d using the Metal Vapour Synthesis (MVS) technique and characterised b y spectroscopic methods. The reactivity displayed by fluorene using MV S is different than for other ligands with acidic hydrogens: cyclopent adiene produces the same eta(5) complexes that can be obtained by more conventional synthesis, while indene (where acidic hydrogens coexist with an aromatic ring) originates both eta(5) or/and eta(6) complexes, sometimes as an isomeric mixture (Mo and W). In the present case of f luorene, only eta(6) complexes were isolated by MVS. In order to expla in this reactivity the stability of Mo and W eta(5) and eta(6) metal c omplexes with fluorene, indene and cyclopentadiene is interpreted usin g Molecular Orbital Calculations by determining the corresponding Over lap Populations. These calculations are also used to explain the chemi cal shifts observed in the H-1 NMR spectra of the bisfluorene complexe s of group 6 metals in terms of p(2) electronic density. (C) 1997 Else vier Science S.A.