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Complexes of Group 3 Metals and Lanthanides That Contain Siloxane‐Bridged Bisaminopyridinato Ligands: Synthesis, Structure, and Application in the Ring‐Opening Polymerization of Lactones
Author(s) -
Noss Henrik,
Oberthür Markus,
Fischer Christine,
Kretschmer Winfried P.,
Kempe Rhett
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199912)1999:12<2283::aid-ejic2283>3.0.co;2-t
Subject(s) - chemistry , ligand (biochemistry) , steric effects , polymerization , ring opening polymerization , lanthanide , ring (chemistry) , monomer , stereochemistry , siloxane , cyclopentadienyl complex , delocalized electron , polyester , moiety , polymer chemistry , medicinal chemistry , crystallography , polymer , catalysis , organic chemistry , ion , biochemistry , receptor
The reaction of one equivalent of dilithiated O(SiMe 2 ‐Ap‐H) 2 [Ap‐H = ‐N(2‐amino‐4‐methylpyridine)] ( 1 ), generated in situ, with LnCl 3 (Ln = Y, Sm) in THF affords O(SiMe 2 ‐Ap) 2 YCl(THF) 2 ( 2 ) or O(SiMe 2 ‐Ap) 2 SmCl(THF) 3 ( 3 ). In contrast, the reaction of one or two equivalents of dilithiated 1 , again generated in situ, with LaBr 3 in THF affords O(SiMe 2 ‐Ap) 2 ) 2 LaLi(THF) 3 ( 4 ). An X‐ray structural analysis of 2 and 3 reveal the O(SiMe 2 ‐Ap) 2– ligand to bind in a planar tetradentate manner. Equivalent Sm–N distances in 3 indicate a delocalized binding mode. Compound 2 reacts with Bu 4 NBH 4 , NaBH 4 or LiCH(SiMe 3 ) 2 to give the corresponding “ate” complexes O(SiMe 2 ‐Ap) 2 Y(BH 4 )Cl(THF) Bu 4 N ( 5 ), O(SiMe 2 ‐Ap) 2 Y(BH 4 ) 2 Na(THF) 2 ( 6 ) and O(SiMe 2 ‐Ap) 2 Y(CH(TMS) 2 ) 2 Li(THF) 3 ( 7 ), respectively. The steric demand of the O(SiMe 2 ‐Ap) 2– ligand is not large enough to stabilize monoalkyl or monoborohydride complexes. Complex 4 has been used as an initiator for the ring‐opening polymerization of ϵ‐caprolactone or δ‐valerolactone. In both cases an almost linear relation between the monomer‐to‐initiator ratio and the molecular weight of the obtained polyester is observed. By conducting the polymerization in neat ϵ‐caprolactone at room temperature a solid polyester block is formed after 3 min (3 g · mol −1 , M w /M n 2.3).