CYCLOPENTADIENYL(ALLYL)(BUTADIENE)HAFNIUM COMPOUNDS - SYNTHESIS, CRYSTAL-STRUCTURE, AND DYNAMICS OF CYCLOPENTADIENYL(1,2,3-TRIMETHYLALLYL)(1,2-DIMETHYLBUTADIENE)HAFNIUM AND CYCLOPENTADIENYL(1,1,2-TRIMETHYLALLYL)(2,3-DIMETHYLBUTADIENE)HAFNIUM

The reaction of CpHfCl3.2THF with 2 equiv of (1,2,3-Me3allyl)MgBr or (1,1,2-Me3allyl)MgBr yields Cp(1,2,3-Me3allyl)(1,2-Me2butadiene)Hf (3) or Cp(1,1,2-Me3allyl)(2,3-Me2butadiene)Hf (4). X-ray crystallography of 3 shows that both the allyl and butadiene ligands assume a prone orientation with respect to Cp. For 3: cell constants a = 15.109 (5), b = 7.150 (2), c = 15.587 (6) angstrom, beta = 115.41 (1)degrees; space group P2(1)/c; R = 0.0305, R(w) = 0.0347. Variable-temperature H-1 NMR studies indicate that compound 3 is static on the NMR time scale whereas 4 exists in two isomeric forms and undergoes three separate dynamic processes involving eta-3-eta-1 isomerization at the unsubstituted and substituted ends of the allyl ligand [DELTA-G double-ended-dagger = 39.4 +/- 1.0 kJ/mol and 73.4 +/- 1.0 kJ/mol, respectively] and butadiene flip [DELTA-G double-ended-dagger (avg) = 49.8 +/- 1.0 kJ/mol].