(Allyl)zirconium(IV) complexes with the N,N'-bis(trimethylsilyl)benzamidinato (''siam'') ligand - Molecular structures and eta(1)-eta(3) interconversions of the allyl groups

Complexes of the type (siam)(2)Zr(allyl)(2) (1a) and (siam)Zr(allyl)(n)Cl-m are described (2a: n = 1, m = 2; 2b: n = 2, m = 1; 2c: n = 3, m = 0; slam: N,N'-bis(trimethylsilyl)benzamidinato group). The molecular structure of la shows that both allyl groups are differently bonded. One allyl ligand is eta(3)-, the other eta(1)-coordinated. The X-ray crystal structure of the tris(allyl) complex 2c shows a chiral molecule with two eta(3)-allyl ligands. The third allyl ligand is coordinated in a mode intermediate between eta(3) and eta(1), thus serving as a model for an intermediate in the eta(3)-eta(1) intramolecular rearrangement of the allyl ligands observed in solution. Temperature-dependent H-1- and C-13-NMR spectra of 1a, 2b and 2c indicate a rapid eta(1)-eta(3) rearrangement of the allyl groups at 60 degrees C. At -50 degrees C two different coordination modes of the allyl groups can be observed in the case of 2b and 2c.