Multistage Activation Barriers in the Chiral Metallosupramolecular Polymerization of Alkynylplatinum(II) Complexes

Abstract

In the process of supramolecular polymerization, kinetic barriers are pivotal in dictating the polymerization pathway and dynamics, thereby intricately modulating both the binding rate and the mechanism involved in the formation of supramolecular polymers. Here, the multistage activation barriers associated with dynamic pathway complexity are reported in the helical metallosupramolecular polymerization of chiral terpyridine-based alkynylplatinum(II) complexes (R-L1-Pt and S-L1-Pt) in a DMSO and H2O mixture (6:4 v/v). The kinetic experiments reveal the presence of a kinetically favored aggregate (Agg-I) that initially forms and subsequently converts to another, more stable kinetic aggregate (Agg-II), accompanied by helicity inversion. Finally, the kinetic aggregate transforms into a thermodynamically favored form (Agg-III) through an additional metal-to-metal ligand charge transfer (MMLCT). The average rate constants (k1 and k2) in nucleation and elongation steps, as well as the activation barriers associated with both kinetic and thermodynamic aggregates, are determined using the Finke-Watzky (F-W) two-step model and the Eyring-type plot method, respectively, confirming that the process follows Eyring behavior. Notably, the activation barrier of the formation of Agg-III is the highest observed. Additionally, the activation barrier is modulated by the addition of Agg-III seeds.