Synthesis and characterization of multidentate ethylene bridged pyrrole- and ketoamine-morpholine aluminum compounds. Structure, theoretical calculation and catalytic study

Pyrrole and keto-amine based morpholine ligands are conveniently synthesized and their corresponding Al-compounds are afforded accordingly. The combination of 1, {C₄H₃NH-2-[CH[dbnd]NCH₂CH₂N(CH₂CH₂)₂O]} and two equivalents of PhNCO generates compound 3, {C₄H₃N(CONPh)CH[sbnd]N(CONPh)(CH₂)₂NC₄H₄O} in relatively high yield. In addition, reacting 1 with one and two equivalents of AlMe₃in toluene render mono- and di-aluminum compounds, AlMe₂{C₄H₃N[2-CH[dbnd]NCH₂CH₂N(CH₂CH₂)₂O]} (4) and AlMe₂{C₄H₃N[2-CH[dbnd]NCH₂CH₂N(CH₂CH₂)₂O]AlMe₃} (5), respectively. Similarly, reactions of morpholine bounded keto-amine ligands OCMeCHCMeNHCH₂CH₂N(CH₂CH₂)₂O (2a) and OCPhCHCMeNHCH₂CH₂N(CH₂CH₂)₂O (2b) with one and two equivalents of AlMe₃result the formation of mono- and di-aluminum compounds, AlMe₂{OCRCHCMeN[CH₂CH₂N(CH₂CH₂)₂O] (6a, R = Me; 6b, R = Ph) and AlMe₂{OCRCHCMeN[CH₂CH₂N(CH₂CH₂)₂O]·AlMe₃(7a, R = Me; 7b, R = Ph), respectively in moderate yield. Compounds 1, 3, 4 and 6b are subjected to X-ray diffraction analysis to ensure the geometry around Al atom. All the aluminum compounds could effectively commence the ring-opening polymerization (ROP) of ε-caprolactone in a well-controlled manner with molecular weight distributions (PDI = 1.08–1.37).