Reinvestigation on the synthesis of hexakis(phenylseleno)benzene

Access to NHC-Boryl Mono- and Bis-Selenide and Utility as Mild Selenium Transfer Reagent Including to the C-F Bond

Reactions of 5-SIDipp ⋅ BH3 (5-SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) (1) with diphenyldiselenide provide access to 5-SIDipp-boryl mono- (5-SIDipp ⋅ BH2 SePh) (2) and bis-selenide (5-SIDipp ⋅ BH(SePh)2 ) (3). The facile cleavage of the B-Se bond makes 2 a neutral source of selenium nucleophiles in substitutions reactions with benzyl bromides, and provide access to the corresponding selenoethers. The direct transformations of one of the C(sp2 )-F bonds of C5 F5 N and C6 F5 CF3 to C-Se bonds have also been achieved by the use of 2 without employing transition-metal catalysts. While it was previously established that C6 F6 could undergo complete defluoroselenation under harsh conditions, we successfully achieved partial defluorination of C6 F6 by employing 2 as a mild selenide transfer reagent. During the formation of C-Se bonds through the cleavage of C-F bonds, the potential by-product NHC ⋅ BH2 F undergoes ring expansion of the NHC, leading to the formation of the six-membered diaazafluoroborinane (7).

Synthesis of benzo[d]imidazo[2,1-b]benzoselenoazoles: Cs2CO3-mediated cyclization of 1-(2-bromoaryl)benzimidazoles with selenium

The synthesis of benzimidazo[2,1-b]benzoselenoazoles is described. The novel ring-closure reaction of 1-(2-bromoaryl)benzimidazoles with Se powder is promoted by Cs₂CO₃ (2 equiv) in DMF at 150 °C. Moreover, the obtained tetracyclic heterocycles are all novel compounds. Single-crystal X-ray analysis of the parent benzimidazo[2,1-b]benzoselenoazole revealed that the tetracyclic ring is almost planar. Absorption spectroscopy data of the benzimidazo[2,1-b]benzoselenoazoles showed the λ_max was dependent on the number of rings.

Crystal structure of 1-bromo-2-(phenyl-selen-yl)benzene

In the title compound, C12H9BrSe, the Se atom exhibits a bent geometry, with a C-Se-C bond angle of 99.19 (6)°. The ortho Se and Br atoms are slightly displaced from opposite faces of the mean plane of the benzene ring [by 0.129 (2) and 0.052 (2) Å, respectively]. The planes of the benzene and phenyl rings form a dihedral angle of 72.69 (5)°. In the crystal, π-stacking inter-actions between inversion-related phenyl rings are observed, with a centroid-centroid distance of 3.630 (1) Å.

Synthesis of protected benzenepolyselenols

Previously unknown benzenepolyselenols have been synthesized and isolated in their acetyl-protected form. The two molecules 1,3,5-tris(acetylseleno)benzene and 1,2,4,5-tetrakis(acetylseleno)benzene were synthesized by the reductive dealkylation in Na/NH(3) of 1,3,5-tris(tert-butylseleno)benzene and 1,2,4,5-tetrakis(tert-butylseleno)benzene, respectively. Hexakis(tert-butylseleno)benzene was also synthesized and structurally characterized by single-crystal X-ray diffraction, but it was not possible to isolate hexakis(acetylseleno)benzene. The synthetic methodology is likely to be useful in the synthesis of other areneselenols.