Synthesis and structural characterization of well-defined anionic aluminum alkoxide complexes supported by NON-type diamido ether tridentate ligands and their use for the controlled ROP of lactide.
The tridentate proligands (RNH-o-C6H4)2O (1a, R = C5H9; 1b, R = Cy) were found to readily react with LiAlH4 to yield the corresponding lithium aluminium dihydrido salt species [eta(2)-N,N-{(RN-o-C6H4)2O}AlH(mu-H)Li(THF)]2 (2a, R = C5H9; 2b, R = Cy) in 50% and 42% yield, respectively. The solid-state structure of both complexes 2a and 2b were determined by X-ray crystallographic studies. Compounds 2a and 2b readily react with one equivalent of benzaldehyde to afford the corresponding mono-benzyloxide species eta(2)-N,N-{RN-o-C6H4)2O}Al(H)(mu-OCH2Ph)Li(THF)2 (4a, R = C4H9; 4b, R = Cy), as confirmed by X-ray studies in the case of 4b. In a similar manner, when compounds 2a and 2b are reacted with two equivalents of benzaldehyde the bis-benzyloxide derivatives 5a and 5b eta(3)-N,N,O-{RN-o-C6H4)2O}Al( -OCH2Ph)2Li(THF)2 (5a, R = C4H9; 5b, R = Cy) may be prepared. While the lithium Al mono-alkoxide species 4a-b are inactive in the ring-opening polymerization (ROP) of lactide, their bis-alkoxide Al analogues 5a-b polymerize rac-lactide and (S)-lactide at room temperature, which is rather uncommon for Al-based alkoxide systems. Kinetic studies of the lactide ROP initiated by compound 5a suggest a strong preference for racemic enchainment during the ROP chain growth; the resulting PLAs are however moderately heterotactic due to detrimental transesterification processes occurring as the chain grows.
Hild
Frédéric
F
Laboratoire DECOMET, Institut de Chimie (UMR CNRS 7177), Université de Strasbourg, 4 rue Blaise Pascal, 67000, Strasbourg, France.
Haquette
Pierre
P
Brelot
Lydia
L
Dagorne
Samuel
S
D000535:Aluminum / Q000737:chemistry*; D017607:Aluminum Compounds / Q000737:chemistry; D000838:Anions / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D008024:Ligands; D018020:Lithium Compounds / Q000737:chemistry; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry
D017607:Aluminum Compounds; D000838:Anions; D056831:Coordination Complexes; D004146:Dioxanes; D008024:Ligands; D018020:Lithium Compounds; D011108:Polymers; C042073:lithium aluminum hydride; C091880:dilactide; D000535:Aluminum