ABC and ABAB Block Copolymers by Electrochemically Controlled Ring-Opening Polymerization.

An electrochemically controlled synthesis of multiblock copolymers by alternating the redox states of (salfan)Zr(OtBu)2 (salfan = 1,1'-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene) is reported. Aided by electrochemistry with a glassy carbon working electrode, an in situ potential switch alters the catalyst's oxidation state and its subsequent monomer (l-lactide, ß-butyrolactone, or cyclohexene oxide) selectivity in one pot. Various multiblock copolymers were prepared, including an ABAB tetrablock copolymer, poly(cyclohexene oxide-b-lactide-b-cyclohexene oxide-b-lactide), and an ABC triblock copolymer, poly(hydroxybutyrate-b-cyclohexene oxide-b-lactide). The polymers produced using this technique are similar to those produced via a chemical redox reagent method, displaying moderately narrow dispersities (1.1-1.5) and molecular weights ranging from 7 to 26 kDa.

An Unsymmetric Ligand Framework for Noncoupled Homo- and Heterobimetallic Complexes.

We introduce a new unsymmetric ligand, PDIpCy (PDI = pyridyldiimine; Cy = cyclam), that offers two distinct, noncoupled coordination sites. A series of homo- and heterobimetallic complexes, [Zn2(PDIpCy)(THF)(OTf)4] (1; THF = tetrahydrofuran and OTf = triflate), [Ni2(PDIpCy)(THF)(OTf)2](OTf)2 (2), and [NiZn(PDIpCy)(THF)(OTf)4] (3), are described. The one-electron-reduced compounds, [Zn2(PDIpCy)(OTF)3] (4), [Ni2(PDIpCy)(OTf)](OTf)2 (5), and [NiZn(PDIpCy)(OTf)3] (6), were isolated, and their electronic structures were characterized. The reduced compounds are charge-separated species, with electron storage at either the PDI ligand (4) or at the PDI-bound metal ion (5 and 6).