Highly 2,3-Selective Polymerization of Phenylallene and Its Derivatives with Rare-Earth Metal Catalysts: From Amorphous to Crystalline Products.

Rare-earth metal complexes (Flu-CH2 -Py)Ln(CH2 SiMe3 )2 (THF)n (Ln=Sc(1), Lu(2), Tm(3), Y(4) and Gd(5)), upon the activation of [Ph3 C][B(C6 F5 )4 ] and Al(i) Bu3 , were employed to catalyze the polymerization of allene derivatives under mild conditions. The Gd, Y, Tm, Lu metal based precursors exhibited distinguished 2,3-selectivity (>99.9 %) for phenylallene (PA) polymerization, whereas the smallest Sc metal based precursor showed a moderate 2,3-selectivity. The activity increased with the central metal size following the trend of Gd(5)>Tm(4)>Y(3)>Lu(2)>Sc(1). Moreover, Gd(5) also realized the purely 2,3-selective polymerizations of polar or nonpolar allene derivatives, para-methylphenylallene, para-flourophenylallene and para-methoxyphenylallene, regardless of electron-donating or -withdrawing substituents. Owing to the highly regular backbones, these polymers (except PPA) were crystalline, thus being the first crystalline polymers based on allene derivatives.