Yttrium bis(alkyl) and bis(amido) complexes bearing N,O multidentate ligands. Synthesis and catalytic activity towards ring-opening polymerization of L-lactide
作者：Xiaomin Shang, Xinli Liu, Dongmei Cui
关键字：activity; alkyl complex; catalysts; biodegradable; polyesters; yttrium
论文来源：期刊
具体来源：http://apps.webofknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=2&SID=V2hxdXl
发表时间：2007年
Methoxy-modified
beta-diimines HL1 and HL2 reacted with Y(CH2SiMe3)(3)(THF)(2) to afford the
corresponding bis(alkyl)s [(LY)-Y-1(CH2SiMe3)(2)] (1) and
[(LY)-Y-2(CH2SiMe3)(2)] (2), respectively. Amination of 1 with 2,6-diisopropyl
aniline gave the bis(amido) counterpart
[(LY)-Y-1{N(H)(2,6-iPr(2)-C6H3)}(2)] (3), selectively. Treatment of
Y(CH2SiMe3)(3)(THF)(2) with methoxy-modified anilido imine HL3 yielded bis(alkyl)
complex [(LY)-Y-3(CH2SiMe3)(2)(THF)] (4) that sequentially reacted with
2,6-diisopropyl aniline to give the bis(amido) analogue
[(LY)-Y-3{N(H)(2,6-iPr(2)-C6H3)}(2)] (5). Complex 2 was "base-free"
monomer, in which the tetradentate beta-diiminato ligand was meridional with
the two alkyl species locating above and below it, generating
tetragonal bipyramidal core about the metal center. Complex 3 was asymmetric
monomer containing trigonal bipyramidal core with trans-arrangement of the amido ligands.
In contrast, the two cis-located alkyl species in complex 4 were endo
and exo towards the 0,N,N tridentate anilido-imido moiety. The bis(amido)
complex 5 was confirmed to be structural analogue to 4 albeit without THF
coordination. All theseyttrium complexes are highly active initiators
for the ring-opening polymerization Of L-LA at room temperature. The catalytic
activity of the complexesand their "single-site" or
"double-site" behavior depend on the ligand framework and the
geometry of the alkyl (amido) species in the correspondingcomplexes.
(c) 2007 Wiley Periodicals, Inc.