Lithium, Magnesium, and Zinc Iminophosphorano(8-quinolyl)methanide Complexes: Syntheses, Characterization, and Activity in ε-Caprolactone Polymerization

Abstract

Lithiation of R2P(CH2C9H6N-8)NBut (R = Ph, 3; R = Pri, 4) with an equivalent of BunLi afforded lithium iminophosphorano(8-quinolyl)methanide [Li{CH(8-C9H6N)P(Ph2)NBut}(THF)] (5) and [Li{CH(8-C9H6N)P(Pri2)NBut}]2 (6), respectively. Reaction of 4 with Et2Mg yielded magnesium iminophosphorano(8-quinolyl)methanide complex (7). Treatment of 6 with ZnCl2 gave [Zn(Cl){CH(8-C9H6N)P(Pri2)NBut}] (8), which was transformed into alkylated zinc complexes [Zn(R1){CH(8-C9H6N)P(Pri2)NBut}] (R1 = Ph, 9; R1 = Me, 10) by treating with R1Li or R1MgX. Ethylzinc complexes [Zn(Et){CH(8-C9H6N)P(R2)NBut}] (R = Ph, 11; R = Pri, 12) were obtained by reaction of 3 or 4 with an equivalent of Et2Zn. Compounds 2 and 4−12 were characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy and elemental analyses. Structures of complexes 6−8 and 10 were further characterized by single-crystal X-ray diffraction techniques. The catalytic behaviors of complexes 7 and 9−12 in the ring-opening polymerization of ε-caprolactone was studied. Complex 7 exhibited high catalytic activity in the presence or absence of benzyl alcohol. Complexes 9−12 catalyzed the ring-opening polymerization of ε-CL in the presence of benzyl alcohol and exhibited first-order dependence on monomer concentration.