Early transition metal and lanthanide metallocenes bearing dihydroazulenide ligands

A generally applicable synthetic protocol for preparing early transition metal and lanthanide metallocenes bearing dihydroazulenide ligands has been developed. Lithium dihydroazulenide precursors such as lithium 4-methyldihydroazulenide ( 2 , = LiC 11 H 11 ), lithium 7-isopropyl-1,4,8-trimethyldihydroazulenide ( 4 , = LiC 16 H 21 ), and lithium 7-isopropyl-1,4-dimethyl-8-phenyldihydroazulenide ( 5 , = LiC 21 H 23 ) were prepared by treatment of azulene or guaiazulene with methyllithium or phenyllithium, resp. While variable-temperature 7 Li NMR revealed the presence of monomeric and dimeric structures in solution, an X-ray diffraction study of the DME adduct LiC 16 H 21 (DME) ( 4a ) showed a monomer with η 5 -coordination of the azulene-derived ligand in the solid state. Reactions of MCl 4 (THF) 2 (M = Ti, Zr) with 2 equivalents of the lithium dihydroazulenides in THF solution provided the Ti and Zr metallocenes 6 – 11 as inseparable mixtures of stereoisomers. However, pure products could be isolated by introducing only one dihydroazulenide ligand as in the mixed-ligand zirconium sandwich complexes (C 5 Me 5 )(C 11 H 11 )ZrCl 2 ( 12A ) and (C 5 Me 5 )(guaiazulenide)ZrCl 2 ( 13 ). In contrast, two related neodymium(III) sandwich complexes containing dihydroazulenide ligands ( 14 , 15 ) also formed mixtures of stereoisomers.