High-Yield Syntheses and Reactivity Studies of 1,2-Diborylated and 1,2,4,5-Tetraborylated Benzenes

Abstract

Treatment of 1,2-dibromobenzene (1,2-C6H4Br2) or 1,2,4,5-tetrabromobenzene (1,2,4,5-C6H2Br4) with 2 equiv or 4 equiv of n-BuLi in the presence of excess iso-propoxy(pinacol)borane ((i-PrO)Bpin) furnishes 1,2-C6H4(Br)(Bpin) (1) or 1,4,2,5-C6H2(Br)2(Bpin)2 (3) with excellent selectivity. The subsequent reaction of 1 or 3 with Mg turnings and more (i-PrO)Bpin gives the di- and tetraborylated benzenes 1,2-C6H4(Bpin)2 (2) and 1,2,4,5-C6H2(Bpin)4 (4) in overall yields of about 65%. For the Grignard transformation step, it is essential to continuously add 1 equiv (1) or 2 equiv (3) of 1,2-dibromoethane as an entrainer over a period of 1 h. Compounds 1 and 2 have been transformed into the ortho-functionalized trihydroborates Li[1,2-C6H4(Br)(BH3)] (Li[7]) and Li[1,2-C6H4(Bpin)(BH3)] (Li[8]) by means of 1 equiv of Li[AlH4]. Using 3 equiv of Li[AlH4], 2 can also be converted into the ditopic lithium trihydroborate Li2[1,2-C6H4(BH3)2] (Li2[9]); even the tetratopic derivative Li4[1,2,4,5-C6H2(BH3)4] (Li4[10]) is accessible from 4 and 4 equiv of Li[AlH4]. The compounds Li[7], Li[8], Li2[9], and Li4[10] have been crystallographically characterized as ether solvates, but still show Ar–BH3-η2-Li interactions as the dominant mode of coordination. In the cases of Li2[9] and Li4[10] an intricate three-dimensional network and a zigzag polymer, respectively, are established by the contact ion pairs in the crystal lattice.

Flapping Peryleneimide as a Fluorogenic Dye with High Photostability and Strong Visible‐Light Absorption

“…[19] S1 was borylated using n BuLi and i PrO-B(pin), giving S2 as syn/anti diborylated isomers. [20] Suzuki-Miyaura coupling of S2 with bromoperyleneimide S3 [21] and subsequent Pd-catalyzed intramolecular CÀH arylation provided FLAP1 (Scheme 1). It should be mentioned that a different combination of coupling partners, S1, and borylated peryleneimide was also attempted, but it was tedious to remove byproducts that had lost bromo substituents before the next arylation step.…”

Boron-rich benzene and pyrene derivatives for the detection of thermal neutrons

“…However, both 1 H and 13 C NMR unambiguously confirmed the synthesis of this molecule ( Figure S5 ). The crystal structure and two-step reaction synthesis of this molecule was published by Wagner et al 27 . More detailed information on the synthesis and characterization of all the materials can be found in the supplementary information.…”

“…In order to counter these disadvantages, the synthesis of 1,3,6,8-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrene was reported by Yamada and coworkers by nickel catalyzed direct borylation achieving a yield of 74% in two days 26 . Furthermore, synthesis of 1,2,4,5-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene was reported by Wagner and coworkers with an overall yield of 64%; however, their synthetic process was a two-step reaction system achieving only partial borylation and the use of highly pyrophoric and toxic reagents such as n-butyllithium and Grignard reagents 27 . Both Aubert et al and Gandon et al utilized cobalt-catalyzed [2+2+2] cycloaddition of ethynyl pinacol borate to yield a mixture of 2,2′,2″-(benzene-1,2,4-triyl)tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene with a yield of 63% 28 29 .…”

Diborylated Magnesium Anthracene as Precursor for B2H5−‐Bridged 9,10‐Dihydroanthracene

“…[28][29][30] Chelating coordination modes as well as coordination polymers have been observed with ditopic hydroborates such as 1,2-bis(trihydroborato)benzene. [31][32][33] Am ore balanced rigidity of the ligand framework, as provided by the DHA backbone in ligands[ H ] 2 À (Scheme 2), is expectedt of urther broaden the range of accessible metal complexes.…”

“…2) The tetrahydroborate ion can establish BHM two‐electron three‐center bonds toward a variety of metal atoms and thereby act as monodentate, bidentate, or tridentate ligand 28–30. Chelating coordination modes as well as coordination polymers have been observed with ditopic hydroborates such as 1,2‐bis(trihydroborato)benzene 31–33. A more balanced rigidity of the ligand framework, as provided by the DHA backbone in ligands [ H ] 2− (Scheme ), is expected to further broaden the range of accessible metal complexes.…”