Photooxidative Generation of Dodecaborate-Based Weakly Coordinating Anions

Abstract

Redox-active proanions of the type B₁₂(OCH₂Ar)₁₂ [Ar = C₆F₅ (<b>1</b>), 4-CF₃C₆H₄ (<b>2</b>), 3,5-(CF₃)₂C₆H₃ (<b>3</b>)] 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 <b>1</b>-<b>3</b> were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (<i>M</i>_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 <b>1</b> in CH₂Cl₂. 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 <b>1</b>-<b>3</b> 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.