Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone.
Dalton Trans
; 53(3): 1346-1354, 2024 Jan 16.
Article
em En
| MEDLINE
| ID: mdl-38164613
ABSTRACT
Anionic donor-functionalized NHC (N-heterocyclic carbene) complexes of Al are rare. We report one such case here, an NHC-aryloxido AlMe2 complex [Al(L)Me2] (2), following a stepwise synthesis from the proligand [HO-4,6-tBu2-C6H2-2-CH2{CH(NCHîCHNAr)}]Br [LH2Br; Ar = 2,6-iPr2-C6H3 (Dipp)] and AlMe3via the zwitterionic intermediate [Al(LH)Me2Br] (1). The ligand's flexibility in 2 is evident from the conformational fluxionality revealed by VT-1H NMR spectroscopic analysis. The â O-Al-C (ca. 100.5°) bite angle is also wider than the â O-Ti-C (ca. 80.6°) as seen in our recently reported Ti complex [Ti(L)(NMe2)2Br]. DFT analysis showed that the CNHC-Al bond is significantly ionic, as is the CNHC-Ti bond. Both 1 and 2 are active in the ring-opening polymerization (ROP) of ε-caprolactone (CL). 2, similar to [Ti(L)(NMe2)2Br], exhibits bifunctional MLC-type monomer activation, but only at an elevated temperature. However, the 2/BnOH combination is catalytically active at room temperature, likely through a zwitterionic [Al(LH)Me2(OBn)]. The 1/BnOH combination follows a similar mechanism but surprisingly at a faster rate.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Dalton Trans
Assunto da revista:
QUIMICA
Ano de publicação:
2024
Tipo de documento:
Article
País de afiliação:
Índia