Organometallic complexes of sequential tetradentate monoanionic ligands and uses thereof in ring opening polymerization of cyclic esters

An organometallic complex represented by Formula IA:

• wherein:
• the dashed line represents a coordinative bond;
• M is zinc, magnesium, or calcium;
• X is a monoanionic ligand;
• A is a bridging moiety of 1 to 12 carbon atoms;
• m is an integer of from 1 to 6, or from 1 to 4, or from 1 to 2;
• n is an integer of from 1 to 6, or from 1 to 4, or from 1 to 2;
• Ra and Rb are each independently hydrogen alkyl, or cycloalkyl, wherein when m is other than 1, Ra and Rb in each (CRaRb) unit can be the same or different, and one or both Ra and Rb in one unit can form a 5-membered, 6-membered or 7-membered alicyclic ring with one or both Ra and Rb of an adjacent unit;
• Rc and Rd are each independently hydrogen, alkyl, or cycloalkyl, wherein when n is other than 1, Rc and Rd in each (CRcRd) unit is the same or different and, optionally, one or both Rc and Rd in one unit form a 5-membered, 6-membered or 7-membered alicyclic ring with one or both Rc and Rd of an adjacent unit;
• R1 and R2 are each independently hydrogen, unsubstituted alkyl, unsubstituted cycloalkyl, benzyl or aryl, or alternatively, one or both of R1 and R2 form together, optionally with one or more carbon atoms in A, a heteroalicyclic or heteroaromatic, 5-membered, 6-membered or 7-membered ring;
• and
• R23-R30 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, halo, heteroalicyclic and heteroaryl,
• wherein said A bridging moiety has a general Formula A1, A2 or A3:
• wherein R5-R12, R15 and R16 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, and aryl,
• R13 and R14 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, and aryl, or, alternatively,
• at least two of R1, R2 and R5-R6 in Formula A1, or at least two of R1, R2 and R7-R10 in Formula A2 or at least two of R1, R2 and R11-R16 in Formula A3 form a 5 to 7-membered alicyclic, heteroalicyclic, aromatic or heterocyclic ring.