The crystal structure of 2,4,4-triphenyl-4H-benzo[b][1,4]oxaphosphinin-4-ium bromide – dichloromethane (1/1), C₂₇H₂₂BrCl₂OP

Source of materials

A modified synthesis that was similar to our previous report was performed [5]. (2-Bromophenyl)diphenylphosphine (2 mmol) and 2-bromo-1-phenylethan-1-one (2.2 mmol) were dissolved in toluene (10 mL) in a Schlenk bottle. After stirring at 90 °C for 3 h, the reaction was cooled to room temperature and then toluene was removed under reduced pressure. The residue is cleaned and then filtered with Et₂O to give the intermediate 2-bromophenyl)(2-oxo-2-phenylethyl)diphenylphosphonium bromide as white solid. The intermediate were dissolved in toluene (10 mL) again and then t-BuOK (4.5 mmol) and Pd(PPh₃)₃ (0.1 mmol) was added under argon gas atmosphere. The reaction mixture was stirred at 110 °C for 5 h, and then it was cooled to room temperature and the toluene was removed under reduced pressure. Some CH₂Cl₂ (10 mL) and water (10 mL) were subsequently added to the resulting mixture. The organic layer was separated, and the aqueous layer was extracted with CH₂Cl₂ (10 mL × 2). All combined organic solutions were dried with anhydrous Na₂SO₄, and the solvent was removed under reduced pressure. The residue was washed by Et₂O to afford the title compound (362 mg, 69%). Crystals of the title compound were obtained by slow evaporation (n-hexane/Et₂O/CHCl₂) within three days.

Experimental details

Coordinates of hydrogen atoms were included using constraints or restraints. Their U_iso values were set to 1.2U_eq of the parent atoms.

Comment

Phosphacycle-based p-conjugated materials have become an attractive research area due to their unique structural and electronic properties of p-block elements [6]. In last decades, most of the research is focusing development of p-conjugated five-membered phosphacycles, especially (benzo)phospholes [7], [8], [9]. Very recently, the six-membered phosphacycles frameworks has gradually attracted attention from material and synthetic chemists [10, 11]. On the other hand, the p-conjugated molecules containing a cationic phosphorus center usually show tunable electron-accepting properties, defining the appealing photophysical and electrochemical characteristics of organophosphorus ionic chromophores [12]. Therefore, six-membered [1,4]oxaphosphonium salts skeletons could have many potential applications in the functional materials research field.

The title structure (see the Figure) contains one 2,4,4-triphenyl-benzo[b][1,4]phosphapyranium cation, one bromine anion, and one dichloromethane solvent molecule. The [1,4]phosphapyranium-core is not perfectly coplanar with a puckering angle of 6.8°. The phosphorous(V) with two phenyl substituents is in a tetrahedral structure. In addition, the obvious interactions between C8–H and bromine anion is observed (distance of C8H–Br is 2.7140(5) Å).