New ligand platforms featuring boron-rich clusters as organomimetic substituents

Abstract

200 years of research with carbon-rich molecules have shaped the development of modern chemistry. Research pertaining to the chemistry of boron-rich species has historically trailed behind its more distinguished neighbor (carbon) in the periodic table. Notably, a potentially rich and, in many cases, unmatched field of coordination chemistry using boronrich clusters remains fundamentally underdeveloped. Our work has been devoted to examining several basic concepts related to the functionalization of icosahedral boron-rich clusters and their use as ligands, aimed at designing fundamentally new hybrid molecular motifs and materials. Particularly interesting are icosahedral carboranes, which can be regarded as 3D analogs of benzene. These species comprise a class of boron-rich clusters that were discovered in the 1950s during the “space race” while researchers were developing energetic materials for rocket fuels. Ultimately, the unique chemical and physical properties of carborane species, such as rigidity, indefinite stability to air and moisture, and 3D aromaticity, may allow one to access a set of properties not normally available in carbon-based chemistry. While technically these species are considered as inorganic clusters, the chemical properties they possess make these boron-rich species suitable for replacing and/or altering structural and functional features of the organic and organometallic molecules—a phenomenon best described as “organomimetic”. Aside from purely fundamental features associated with the organomimetic chemistry of icosahedral carboranes, their use can also provide new avenues in the development of systems relevant to solving current problems associated with energy production, storage, and conversion.

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

“…Using this organomimetic strategy 29 , we show that one can mimic the rigid surface of a Au-based nanoparticle core while producing assemblies that are fully covalent and thus stable under relatively harsh conditions (Fig. 1).…”

“…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.…”

Coordinating Ability of the Iminophosphorane Group in ortho‐Carborane Derivatives

“…However, the main application for exo ‐metallated carborane derivatives is in the field of catalysis , . Although the o ‐carborane moiety usually gets used because of its stability and bulky character,, the different inductive effects of the o ‐carborane moiety have also been used to modulate the coordinating ability of vicinal sulfur and phosphorus donor atoms in coordination compounds. Thus, a thioether group shows reduced donor ability when connected to a C‐ m ‐carboranyl moiety, but presents enhanced donor strength when connected to the antipodal boron atoms of o ‐ and m ‐carborane groups .…”

N,O-Type Carborane-Based Materials

“…Our interest in N/O-functionalized carboranes primarily stems from our rationale that introducing a carborane moiety in the place of a conventional carbon-based moiety would strongly influence the coordination chemistry of such compounds, in addition to other relevant properties, such as higher stability, hydrophobicity, etc. Integration of carboranes in place of organic ring systems (typically benzene) is a very popular strategy to trigger desirable properties in (bio)medicine [7,8] but is much less exploited in chemistry or materials science [35].…”