Visible-Light-Induced Olefin Activation Using 3D Aromatic Boron-Rich Cluster Photooxidants

Abstract

Local Identifier(s): UCPMS ID: 1604555eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. Abstract:We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B12(OCH2Ar)12 (Ar = Ph or C6F5) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B12(OCH2C6F5)12 in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations.

Atomically precise organomimetic cluster nanomolecules assembled via perfluoroaryl-thiol SNAr chemistry

“…Notably, the initially dark red solution quickly turned colorless. 11 B NMR spectroscopy of this colorless solution revealed a singlet resonance at δ −15 characteristic of a reduced cluster in a [ 2 ] 2- oxidation state 35,36 , which is consistent with the reducing capacity of the thiolate species when exposed to [ 2 ] 0 (Fig. 2d).…”

“…1). Specifically, we demonstrate how dodecaborate clusters 29,31–36 featuring a dense layer of rigid pentafluoroaryl functional groups can serve as excellent scaffolds for constructing atomically precise, multivalent organomimetic cluster nanomolecules (OCNs). The perfluoroaryls are able to undergo facile “click”-like nucleophilic aromatic substitution (S N Ar) with a wide range of thiols at room temperature within hours, creating robust carbon–sulfur bonds (80–90 kcal/mol) 37 , thereby producing nanomolecules decorated with well-defined functional surfaces.…”

Synthesis and Applications of Perfunctionalized Boron Clusters

“…43 Given our interest in the development of chemistry and applications of perfunctionalized boron clusters, 44–46 we reexamined the reactivity of the closo -[B 6 H 7 ] 1− anion. Under microwave heating conditions, the hexaborate anion can be substituted with benzyl bromide electrophiles (Fig.…”

“…By utilizing blue LEDs as a light source under controlled conditions, we demonstrated that the perfunctionalized cluster hypercloso -B 12 (OCH 2 Ph) 12 can behave as a powerful photooxidant in the visible light-assisted polymerization of olefins. 46 The proposed mechanism involves the generation of a potent photooxidant by visible light promotion of an electron from a low lying occupied orbital localized largely on the aryl rings and oxygens to the cluster-based LUMO (Fig. 9A).…”

The chemical bonding and spectral assignments of rhodium(III)-catalyzedcloso-dodecaborate complexes: Ab initio study

“…It is well‐known that the boron hydrides (boranes) have attracted a lot of attention because of their potential applications in drug delivery, photoredox catalysts, and materials science, especially for icosahedral [B 12 H 12 ] 2− ( closo ‐dodecaborate) cluster with 12 identical B‐H vertices, that provides the fascinating physicochemical properties serving as building blocks in such diverse areas.…”