Living ROMP Synthesis and Redox Properties of Triblock Metallocopolymers Containing Side-Chain Iron and Cobalt Sandwich Complexes

Metalloblock copolymers are intensively researched because of their multifunctionalities and potential applications in biomedicine and materials science. In addition, metal fragments with redox stabilities are of interest toward conductors, sensors, and batteries. Here, Grubb's third-generation metathesis catalyst is efficiently used in ring-opening metathesis polymerization (ROMP) reactions leading to the synthesis of two triblock metallopolymers in which each block contains a redox-reversible iron or cobalt sandwich site. For each metallocopolymer, among six possibilities, only one involving a precise order of introduction of blocks is efficient with the completion of 25 units per block. Cyclic voltammetry measurements show the respective ability of the metal centers to exchange electrons with the electrode, with some electron transfer paths being marred by the positive charges and ligand bulk. Overall, these systems provide a cascade of chemically reversible electron transfers, their number being reasonably estimated using the empirical Bard-Anson model within approximately 20% of the number of redox sites determined by H-1 NMR.