Alkali Metal Complex–Mediated Ring-opening Polymerization of rac-LA, ε-Caprolactone, and δ-Valerolactone

Panda, Tarun K and Harinath, A and Bhattacharjee, Jayeeta and Sarkar, Alok (2019) Alkali Metal Complex–Mediated Ring-opening Polymerization of rac-LA, ε-Caprolactone, and δ-Valerolactone. New Journal of Chemistry. ISSN 1144-0546

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Abstract

A series of alkali metal complexes formed by N-(2-fluoro/2-nitro phenyl)-P,P-diphenylphosphinoselenoic amide [(Ph2P(Se)NH(2-RC4H4)] [R = F (1-H); NO2 (2-H)] ligands with molecular formulas [M(THF)2(Ph2P(Se)N(2-RC4H4)] [M = Li, R = F (3a), NO2 (3b)] and [M(THF)2(Ph2P(Se)N(2-RC4H4)] [M = Na, R = F (4a), NO2 (4b); M = K, R = F (5a), NO2 (5b)] have been synthesized in great yield and fully characterized. The molecular structures of protic-ligands 1-H and 2-H, and alkali metal complexes 3b, 4a, and 4b were analyzed using single-crystal X-ray diffraction analysis. Sodium and potassium complexes 4a,b and 5a,b were proved to be active catalysts for the ring-opening polymerization (ROP) of rac-LA (rac-LA), ε-caprolactone, and δ-valerolactone at room temperature only. The best isoselectivity of poly(lactide) (PLA) was achieved to a high value of Pi = 0.78 using sodium complex 4b. One exceedingly dynamic potassium complex (5a,5b) even can catalyze the polymerization of 1,000 counterparts of rac-LA and yield polylactide with a high molecular weight and narrow polydispersity record (PDI). Experimental outcomes also showed steric hindrance, and electronic impacts have noteworthy consequences for this catalysis in the ROP of rac-LA.

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