Bis(phosphangulene)iminium Salts. Holding on to Fullerenes with Phangs

Abstract

Phosphangulene (“Phang”) is an analogue of triphenylphosphine with a conical shape and electron-rich aromatic surface that complements the electron-poor surface of fullerenes, both geometrically and electronically. Large molecular surfaces with multiple areas of concavity can be made by grafting units of Phang onto selected cores, using the ability of phosphorus to form covalent bonds with many other elements. Incorporating multiple conical subunits of Phang creates molecules that are awkwardly shaped, unable to pack efficiently, and predisposed to form cocrystals. To demonstrate the potential of this approach, we made salts of the bis­(phosphangulene)­iminium cation ([(Phang)2N]+), in which the phosphorus atoms of two Phang groups are bonded to a single atom of nitrogen. Analysis of the structures of various salts shows that [(Phang)2N]+ has a unique ability to stabilize unusual anions, including those incorporating fullerenes.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…Wuest et al reported X-ray crystal structures of various polymorphs of phosphangulene chalcogenides 116.2a – c 235 and those of the various solvates originating from the cocrystallization of 116.2a – c with C 60 or C 70 . 236 Furthermore, they characterized the crystal structures of the bis(phosphangulene)iminium salts (including [ 116.9 ][Br]) 237 and the silver(I) ( 116.10 + ) and copper(I) ( 116.11 + ) complexes featuring a metal center that is tetracoordinated by phosphangulene ( Scheme 116 ). 238 …”

Phosphangulene: A Molecule for All Chemists

“…Growth Des. 2020 , 20, 1319–1327 . A simple way to make molecules with large curved aromatic surfaces is to graft multiple units of phosphangulene onto suitable cores by exploiting the ability of phosphorus to form strong covalent bonds with other elements.…”

“…Molecules with large curved aromatic surfaces can be made by complex multistep syntheses, but a simpler approach is to graft multiple units of phosphangulene onto suitable cores by exploiting the ability of phosphorus to form strong covalent bonds with other elements. This strategy can be illustrated by synthesis of the bis­(phosphangulene)­iminium cation (abbreviated as [(Phang) 2 N] + ) . The related cation [(Ph 3 P) 2 N] + is widely used in chemistry, and over 1000 structures of its salts have been reported since the cation was first reported in 1961. − [(Ph 3 P) 2 N] + has special properties that appear to arise from its globular shape and large aromatic surface. − In particular, it is weakly coordinating, yields salts with enhanced solubility in organic solvents, facilitates crystallization, and stabilizes reactive anions.…”

“…Certain molecules are exceptional and attract wide curiosity. Among these special cases is phosphangulene ( 1 ), which can be viewed from diverse perspectives and be broadly embraced as a molecule worth special attention. − The compound was first reported in 1997 by Krebs et al, who devised an efficient five-step synthesis (Scheme ) and described the structure of crystals grown from ethyl acetate (Figure ), which is the only form reported so far. Phosphangulene is conical, and a dipole moment of 3.3 ± 0.2 D (CHCl 3 ) runs along the C 3 axis from the apex of the cone to the base, with phosphorus at the negative end …”

“…2020, 20, 1319−1327. 3 A simple way to make molecules with large curved aromatic surfaces is to graft multiple units of phosphangulene onto suitable…”