Comparative Study of Lactide Polymerization with Lithium, Sodium, Potassium, Magnesium, Calcium, and Zinc Azonaphthoxide Complexes

A series of lithium, sodium, potassium, magnesium, calcium and zinc azonaphthoxide complexes [M(κ m ‐{2‐O(C 10 H 6 )N=N(C 6 H 4 R)})] n (R = H, m = 2; M = Li 1 , Na 2 , K 3 ; R = OMe, m = 3; M = Li 4 , Na 5 , K 6 ) and [M(κ m ‐{2‐O(C 10 H 6 )N=N(C 6 H 4 R)}) 2 ] n (R = H, m = 2; M = Mg 7 , Zn 8 , Ca 9 ; R = OMe, m = 3; M = Mg 10 , Zn 11 , Ca 12 ) have been synthesized and fully characterized. The solid‐state molecular structures of the zinc complexes 8 and 11 and the magnesium derivative 10 have been determined by X‐ray diffraction studies. The alkali‐metal compounds 1 – 6 are extremely active catalysts for the ring‐opening polymerization (ROP) of L ‐lactide. A catalytic‐activity study has been performed by varying the metal complex and the coordination sphere of the metal in the presence and absence of a coinitiator. Stoichiometric reactions involving the catalysts, BnOH and lactide have been performed to elucidate mechanistic aspects related to the polymerization of L ‐lactide.