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The series of half-sandwich metallocenes of group 4 metals containing the C,N-chelating ligand (η5-C5Me4R)MCl2(C6H4CH2NMe2-κ2C,N) (M = Ti(1), Zr(2), Hf(3); R = Me(C), H(D)) were prepared by reacting the corresponding pentamethyl- and tetramethyl-substituted cyclopentadienylmetal trichlorides (η5-C5Me4R)MCl3 (M = Ti(1), Zr(2), Hf(3); R = Me(A), H(B)) with 2-[(dimethylamino)methyl]phenyl lithium. The X-ray crystal structure analysis of 1C–3C showed that they are isostructural/isomorphous containing two pairs of enantiomers in a P21/c unit cell, whereas crystals of 2D and 3D contained only one enantiomer in a P212121 unit cell. The presence of enantiomers in solution was resolved in variable temperature 1H NMR spectra below the temperature of signal coalescence. The transition state for interconversion of the two enantiomers for 1C was identified by DFT results to be on a 2nd order saddle point. Synthesis of η5-tetramethylcyclopentadienylmetal trichlorides 2B and 3B and their tetrameric and dimeric crystal structures are also reported. |
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