Dinuclear Pentacoordinated Organoyttrium Biphenolates as Initiators for the Synthesis of High-Molecular Weight Isotactic Poly(2-vinylpyridine)

Dinuclear
organoyttrium biphenolato complexes have been synthesized for the
first time starting from Y­(CH2SiMe3)3(THF)2 and readily available biphenols with bulky substituents
at the 3,3′-positions. XRD analysis revealed that these complexes
are formed as homochiral dimers even though racemic biphenols were
employed. Such dinuclear penta-coordinated yttrium complexes were
evaluated as initiators in the polymerization of 2-vinylpyridine (2-VP).
High activity and excellent isotacticity (mm > 99%) were observed.
DSC analysis of poly­(2-VP) showed a Tm = 221 °C, which is the highest value reported to date. Attempts
to improve the low initiation efficiency of the present system were
made by co-use with several organo-main-group metal reagents. Specifically,
good molecular weight control within the high Mn region was achieved by the addition of Et3Al (Al/Y
= 10).