Methyl- and propylacetamidinates of lanthanides: Structures, catalytic and some physical properties

The acetamidinates {[MeNC(Me)NMe]2Ln}2[μ-η2-η2-MeNC(Me)NMe]2 (Ln = Y (1), Dy (2)) and {[PrnNC(Me)NPrn]2Y}2[μ-η2-η2-PrnNC(Me)NPrn]2 (3) have been prepared by the reactions of amides Ln[N(SiMe3)2]3 with respective N,N′-disubstituted amidines MeNC(Me)NHMe or PrnNC(Me)NHPrn. The reaction of Er[N(SiMe3)2]3 with excess of monosubstituted amidine HNC(Me)NHPri or in a ratio of 1:2 resulted in the formation of compound {Er[NC(Me)NHPri]3}x (4). The same reaction with 1:1 ratio yielded heteroleptic complex {Er[N(SiMe3)2]2[NC(Me)NHPri]}x (5). The complexes 1, 2 and 3 have similar structures and contain four terminal and two μ-η2:η2-N,N-bridging amidinate groups binding the metal atoms. Volatility of 1, 2 and 3 is comparable to that of known monomeric La[PriNC(R)NPri]3. Compound 1 efficiently catalyzes the ring-opening polymerization of rac-lactide to give polylactide with Mn 53 085 and polydispersity 1.84.