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

Article abstract of DOI:10.1021/om00050a033

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) A?, β = 115.41 (1)°; space group P2₁/c; R = 0.0305, R_w = 0.0347. Variable-temperature ¹H 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 η³-η¹ isomerization at the unsubstituted and substituted ends of the allyl ligand [ΔG? = 39.4 ± 1.0 kJ/mol and 73.4 ± 1.0 kJ/mol, respectively] and butadiene flip [ΔG?(avg) = 49.8 ± 1.0 kJ/mol].