137919-01-8Relevant academic research and scientific papers
Synthesis of ((dimethylamino)alkyl)zirconocene complexes and their dynamic behavior
Pl?ssl, Karl,Norton, Jack R.,Davidson, James G.,Barefield, E. Kent
, p. 534 - 539 (1992)
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.
