STRUCTURES, DYNAMICS, AND REACTIVITY OF TRIPODAL AMIDO LIGANDS COORDINATED TO TIIV CENTERS

A new class of amido titanium(IV) halides containing tripodal ligands H3CC(CH2NR)3TiX (R = Me, X = Cl: 1; R = Me3Si, X = Cl: 2a, Br: 2b; R = SiMe2tBu, X = Cl: 3a, Br: 3b) has been synthesised. Compound 1 has been structurally characterised by X-ray crystallography and found to be dimeric in the crystal displaying an idealised C2 symmetry with bridging amido functions linking the two halves of the molecule. The dimeric structure is retained in solution as has been shown by H-1- and C-13-NMR spectroscopy which has also revealed a high degree of ligand dynamics, effecting the interconversion of the two enantiomeric forms of the molecule. This process has been investigated by variable temperature NMR studies and phase-sensitive H-1-NOESY/EXSY spectra. The dimeric mu-imido complexes [H3CC(CH2NSiMe3)2(H)CH2NTiX]2 (X = Cl: 4a, Br: 4b) have been isolated as a byproduct in the synthesis of 2a/b, and a single-crystal X-ray structure analysis of 4a has established its molecular structure.