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

Abstract

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·BH2SePh) (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 C6F5N and C6F5CF3 to C‐Se bonds have also been achieved by the use of 2 without employing transition‐metal catalysts. While it was previously established that C6F6 could undergo complete defluoroselenation under harsh conditions, we successfully achieved partial fluorination of C6F6 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·BH2F undergoes ring expansion of the NHC, leading to the formation of the six‐membered diaazafluoroborinane (7).

Saturated NHC-Stabilized Borenium, Boronium, Hydride-Bridged Boron Cations, and a Bora-Acyl Chloride

“…11−13 For example, very recently, we have reported 5-SIDipp stabilized boryl mono and bis selenides, which can be used as selenium transfer reagents even to aromatic C−F bonds. 13 stimulated us to investigate the same reaction with 5-SIDipp, which is a stronger σ-donor than 5-IDipp but poorer with respect to 6-SIDipp. While we were able to structurally characterize the intermediate proposed by the groups of Curran and Vedejs, we also found that the compound is very unstable and undergoes hydrolysis quickly.…”

“…While we were recently engaged in developing boron chemistry mostly with 6-SIDipp (6-SIDipp = 1,3-di­(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene), ,− we have also begun to explore 5-SIDipp (5-SIDipp = 1,3-bis­(2,6-diisopropylphenyl)-imidazolin-2-ylidene) in boron chemistry. − For example, very recently, we have reported 5-SIDipp stabilized boryl mono and bis selenides, which can be used as selenium transfer reagents even to aromatic C–F bonds . These two different results from two different NHCs stimulated us to investigate the same reaction with 5-SIDipp, which is a stronger σ-donor than 5-IDipp but poorer with respect to 6-SIDipp.…”

“…The solution part was cannulated and reduced to yield colorless crystals of 1 at 4 °C. Due to rapid hydrolysis of 1 in any deuterated solvents, we are unable to provide satisfactory 1 H and13 C spectra 11. B{ 1 H} NMR (128 MHz, 298 K, CDCl 3 ): δ = −24.1 (bs, 1B, BHB) ppm.…”

“…Organometallics pubs.acs.org/Organometallics Article https://doi.org/10.1021/acs.organomet.4c00139 Organometallics XXXX, XXX, XXX−XXX D i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .literature procedure. The 1 H,13 C, and 11 B NMR spectra were recorded in CDCl 3 using a Bruker Avance DPX 400 and a Bruker Avance DPX 500 spectrometer. Chemical shifts (δ) are given in ppm.…”