Lanthanum Tribenzyl Complexes as Convenient Starting Materials for Organolanthanum Chemistry

Simple tribenzyl complexes of lanthanum, [La(CH2C6H4-4-R)3(THF)3] (R = H (1a), Me (1b)), were
prepared in a remarkably straightforward fashion from LaBr3(THF)4 and potassium benzyl reagents. Single-crystal X-ray diffraction revealed a fac arrangement of the three THF ligands and η2 binding of the
benzyl groups. These compounds are convenient precursors to other organolanthanum complexes. Reaction
of 1a with the amidine ArNCPhNHAr (Ar = 2,6-Pri2C6H3) affords the corresponding mono(amidinate)
dibenzyl derivative 2. Complex 1b reacts with LiCH2C6H4-4-Me to give the THF-free anion [La(CH2C6H4-4-Me)4]- (3). Reactions of 1 with 1 or 2 equiv of [PhNMe2H][B(C6X5)4] (X = H, F) generate the
corresponding mono- and dicationic benzyl species [La(CH2C6H4-4-R)2(THF)4]+ (4) and [La(CH2C6H4-4-R)(THF)6]2+ (5), which were structurally characterized. Scouting ethylene polymerization experiments
indicate that these species are only modestly active catalysts but suggest that the monocationic dibenzyl
species is more efficient. Both neutral and cationic lanthanum benzyl complexes effect the catalytic
intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine. It was also observed that
polycationic La species without ancillary ligands effectively catalyze the isomerization of the substrate
to (E)-2,2-dimethyl-3-pentenylamine.