Photooxidative Generation of Dodecaborate-Based Weakly Coordinating Anions

Abstract

Redox-active proanions of the type B_(12)(OCH_2Ar)_(12) [Ar = C_6F_5 (1), 4-CF_3C_6H_4 (2), 3,5-(CF_3)_2C_6H_3 (3)] are introduced in the context of an experimental and computational study of the visible-light-initiated polymerization of a family of styrenes. Neutral, air-stable proanions 1–3 were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (M_n) ranging from ∼6 to 100 kDa. Shorter polymer products were observed in the majority of experiments, except in the case of monomers containing 4-X (X = F, Cl, Br) substituents on the styrene monomer when polymerized in the presence of 1 in CH_2Cl_2. Only under these specific conditions are longer polymers (>100 kDa) observed, strongly supporting the formulation that reaction conditions significantly modulate the degree of ion pairing between the dodecaborate anion and cationic chain end. This also suggests that 1–3 behave as weakly coordinating anions (WCA) upon one-electron reduction because no incorporation of the cluster-based photoinitiators is observed in the polymeric products analyzed. Overall, this work is a conceptual realization of a single reagent that can serve as a strong photooxidant, subsequently forming a WCA.