Zinc complexes incorporating with symmetrical and asymmetrical polydentate nitrogen-donor pyrrolyl ligands: Synthesis, characterization, and ring-opening polymerization

The reactions of Zn-alkyls with bidentate as well as symmetrical and asymmetrical tridentate pyrrolyl ligands, have been carried out and characterized. Reacting ZnR2 with 1 equiv of C4H3NH(2-CH2NHtBu) in diethyl ether yields [Zn{C4H3N(2-CH2NHtBu)}R] (1, R = Me; 2, R = Et) in high yield. Similarly, the reactions of 2 equiv of C4H3NH(2-CH2NHtBu) and ZnR2 (R = Me, Et) in toluene both produce [Zn{C4H3N(2-CH2NHtBu)}2] (3). Furthermore, while subjecting 2 equiv of C4H2NH(2-CH2NHtBu)(5-CH2NMe2) with ZnMe2 in diethyl ether, affords [Zn{C4H2N(2-CH2NHtBu)(5-CH2NMe2)}2] (4) and additionally, reacting C4H2NH(2,5-CH2NHtBu)2 with ZnMe2 generates [Zn{C4H2N(2,5-CH2NHtBu)2}2] (5) in satisfactory yield. All the aforementioned compounds were characterized by 1H and 13C NMR spectrometry and the molecular structures were determined by single crystal X-ray diffractometry. Compounds 1, 3, 4 and 5 are moderate catalysts for the ring-opening polymerization of ε-caprolactone in toluene.