Lithium, magnesium, and zinc iminophosphorano(8-quinolyl)methanide complexes:: Syntheses, characterization, and activity in ε-caprolactone polymerization

Lithiation of R2P(CH2C9H6N-8)NBut (R = Ph, 3; R = Pr-i, 4) with an equivalent of (BuLi)-Li-n afforded lithium iminophosphorano(8-quinolyl)methanide [Li{CH(8-C9H6N)P(Ph-2)NBut}(THF)] (5) and [Li{CH(8-C9H6N)P(Pr-2(i))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(Pr-2(i))NBut}] (8), which was transformed into alkylated zinc complexes [Zn(R-1){CH(8-C9H6N)P(Pr-2(i))NBut}] (R-1 = Ph, 9; R-1 = Me, 10) by treating with (RLi)-Li-1 or (RMgX)-Mg-1. Ethylzinc complexes [Zn(Et){CH(8-C9H6N)P(R-2)NBut}] (R = Ph, 11; R = Pr-i, 12) were obtained by reaction of 3 or 4 with an equivalent of Et2Zn. Compounds 2 and 4-12 were characterized by H-1, C-13{H-1}, and P-31{H-1} 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 epsilon-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 epsilon-CL in the presence of benzyl alcohol and exhibited first-order dependence on monomer concentration.