Synthesis of ((dimethylamino)alkyl)zirconocene complexes and their dynamic behavior

Article abstract of DOI:10.1021/om00038a006

PhCH(K)NMe₂ and LiCH₂NMe₂ react with zirconocene or hafnocene chlorides in THF to give satisfactory yields of their (dimethylamino)alkyl derivatives. Cp₂Zr(R)CH(Ph)NMe₂ (R = Cl, 5; R = Me, 6) was prepared by treating Cp₂Zr(R)Cl with PhCH(K)NMe₂. Cp(η⁵-C₅H₄R)M(Cl)CH₂N(CH ₃)₂ (M = Zr, X = Cl, R = H, 7; M = Hf, X = Cl, R = H, 8; M = Zr, X = Cl, R = CPh(CH₃)₂, 11) was prepared by treating the appropriate metallocene dichloride with LiCH₂N(CH₃)₂. Acidic reagents (CF₃CO₂H, CpMo(CO)₃H, [M-Bu₃NH][BPh₄]) cleaved the methyl ligand from 6 and gave the ^-O₂CCF₃ complex (10), the ^-(μ-OC)Mo(CO)₂Cp complex (12), or the solvated cation (13). Complex 7 did not react with excess LiCH₂N(CH₃)₂, LiPh, MeI, CO(g) (1 atm), or Na(Hg), but a low yield of its methyl derivative was obtained by treating it with LiCH₃. The inequivalence of the N-methyl groups in the ¹H NMR spectra of complexes 5, 6, and 10-13 at low temperatures showed that the CH(R)NMe₂ ligands were bound in an η² fashion. Simulation of the temperature-dependent ¹H NMR spectra of CDCl₃ solutions of 11 gave ΔH^? and ΔS^? values of 17.1 ± 0.8 kcal/mol and 2.3 ± 2.7 eu, respectively, for N-methyl exchange. The Zr-N interaction energy in 11 can thus be estimated at 8 kcal/mol.